Research ArticleShort-Term Changes in Light Distortion inOrthokeratology Subjects
Elena Santolaria Sanz12 Alejandro Cervintildeo2 Antonio Queiros3 Cesar Villa-Collar4
Daniela Lopes-Ferreira3 and Jose Manuel Gonzaacutelez-Meacuteijome3
1Private Practice Onda 12200 Castellon Spain2Optometry Research Group Department of Optics Universidad de Valencia 46100 Valencia Spain3Clinical amp Experimental Optometry Research Lab (CEORLab) Center of Physics (Optometry) Universidade do Minho4710-057 Braga Portugal4Department of Optics and Optometry Universidad Europea de Madrid 28670 Villaviciosa de Odon Spain
Correspondence should be addressed to Jose Manuel Gonzalez-Meijome jgmeijomefisicauminhopt
Received 21 June 2014 Revised 17 November 2014 Accepted 1 December 2014
Academic Editor Terri L Young
Copyright copy 2015 Elena Santolaria Sanz et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited
Purpose Quantifying adaptation to light distortion of subjects undergoing orthokeratology (OK) for myopia during the first monthof treatment Methods Twenty-nine healthy volunteers (age 2234 plusmn 808 years) with mean spherical equivalent refractive errorminus210 plusmn 093D were evaluated at baseline and days 1 7 15 and 30 of OK treatment Light distortion was determined using anexperimental prototype Corneal aberrations were derived from corneal topography for different pupil sizes Contrast sensitivityfunction (CSF)was analyzed for frequencies of 150 212 300 424 600 849 1200 1697 and 2400 cpd under photopic conditionsResults Averagemonocular values of all light distortion parameters measured increased significantly on day 1 returning to baselineafter 1 week (119875 lt 005 in all cases) Spherical-like aberration stabilized on day 7 for all pupil diameters while coma-like for smallerpupils only CSF was significantly reduced on day 1 for all spatial frequencies except for 15 cpd returning to baseline afterwardsSignificant correlation was found between light distortion and contrast sensitivity for middle and high frequencies (119875 lt 005) after15 days Conclusion Despite consistently increased levels of corneal aberrations light distortion tends to return to baseline afterone week of treatment suggesting that neural adaptation is capable of overcoming optical quality degradation
1 Introduction
Modern corneal refractive therapy (CRT) or orthokeratology(OK) aims to reshape the anterior corneal surface by theovernight application of reverse geometry contact lenses(CL) In the case of myopia correction the central corneais flattened to achieve the desired reduction in the powerof the anterior corneal surface while the midperipheralcornea steepens [1 2] as a result of the epithelial thicknessredistribution from the corneal center These histologicalmodifications occurring in orthokeratology [3 4] drive achange in the optical quality of the cornea significantlyincreasing spherical aberration in the positive direction [56] with an impact on visual quality particularly under lowluminance conditions [7ndash9]
In clinical practice OK subjects used to complain ofdysphotopic phenomena in the form of haloes ghosting orglare These phenomena are described as more intense at thebeginning of the treatment period and decrease over time [810] and might also be associated with a loss in visual qualitybut none of them has been analyzed further yet Indeed it isassumed that the increase in corneal higher order aberrationsand related optical quality degradation will remain duringthe treatment [11] thus we hypothesize that the increase inlight distortion phenomena is a transient process that mightbe independent of the optical quality changes in the cornealsurface and might have an impact on visual quality
The purpose of this study was to evaluate the time-course variations in the size of light distortion phenomenameasured with an experimental device and correlate them
Hindawi Publishing CorporationBioMed Research InternationalVolume 2015 Article ID 278425 7 pageshttpdxdoiorg1011552015278425
2 BioMed Research International
with the aberrations of the anterior corneal surface andcontrast sensitivity function (CSF) over the first month oftreatment
2 Methods
A total of 29 neophyte subjects were recruited and fittedwith OK lenses for myopia correction with reverse geometryrigid gas permeable CL Inclusion criteria required that theybe over 18 years of age have less than 100 diopters (D)of refractive astigmatism be free of ocular disease haveno contraindication for overnight CL wear and present abest spectacle corrected monocular visual acuity of 090decimal (2025) or better Subjects were followed up and theywore their lenses successfully for 1 month Demographic andrefractive data of subjects are presented inTable 1 All subjectsenrolled achieved a satisfactory correction and no dropoutswere observed during the 1-month follow-up time
Subjects were informed of the purpose of the study andsigned a consent form after all their questions were answeredfollowing the tenets of the Declaration of Helsinki Subjectsunderwent a comprehensive optometric examination prior toenrollment
21 Outcome Measures Visual acuity was measured underphotopic conditions at 5m using a decimal scale chartSubjective baseline refraction and refraction at the time ofdata collection were determined as the spherocylindricalcombination that rendered the best distance visual acuitywith the highest positive power
Light distortion was analysed with an experimental pro-totype consisting of a central light emitting diode (LED)surrounded by 240 small LED sources distributed in 24semimeridians with an angular separation of 15∘ For the pur-pose of the present experiment an angular separation of 30∘was considered Figure 1 represents the arrangement of thecentral white LEDs and the surrounding smaller white LEDsThe central LED was a commercially available white LEDfrom Agilent Technologies (ref HLMP-CW47-RU000 fromAgilent Technologies Inc Berkshire United Kingdom) thesurrounding LEDs were commercially available white LEDsfrom Avago Technologies (ref HSMW-CL25 from AvagoTechnologies San Jose California United States)The subjectwas at a distance of 20m in a darkened room The physical(electronic board) display device is connected to a centralcontrol device (PC) via USB connection when heshe candetect a peripheral LED as this is moving from the innerpart to the outer part of the area of examination The subjectbeing evaluated provides feedback to the system througha remote response device (PC mouse) Peripheral stimuliare presented around the central source of light from theinner to the outer part of the field at random times rangingfrom 250 to 750 milliseconds Semimeridians are exploredin random order When the subject sees the stimulus heshepresses the mouse control and the system presents the nextsemimeridian Further description of the device can be foundelsewhere [12] After data collection and storage a softwaretool then calculates three indices that determine the size and
Table 1 Demographic refractive and keratometric data of subjects(mean plusmn SD) and range (minimum and maximum)
Age 2234 plusmn 808 years (18ndash43)Sample (malefemale ratio) 29 subjects (623)M (baseline) minus210 plusmn 093D (minus100 to minus475)J0 (baseline) minus003 plusmn 014D (minus050 to 046)J45 (baseline) 000 plusmn 008D (minus029 to 036)Flattest keratometric radius 778 plusmn 028mm (720 to 864)Steepest keratometric radius 755 plusmn 029mm (692 to 852)Decimal VA (monocular) 116 plusmn 009 (090 to 150)
Figure 1 Distribution of main central source of light and peripheralstimuli
regularity of the distortion surrounding the central source oflight
The Best Fit Circle Radius (BFCr) is defined as the circlethat best fits the distortion area resulting from the linearbinding of all points in each meridian of the device Thisparameter is expressed in mm and is linearly related to theDistortion Index (LDI) parameter
LDI is calculated as the ratio of the area or points missedby the subject and the total area explored and is expressed asa percentage () The higher values of distortion (BFCr andLDI) are interpreted as a lower ability to discriminate smallstimuli surrounding the central light source
The irregularity of the distortion area is derived as thedeviation of the actual polygonal shape obtained from theBFC fit and is called the BFC Irregularity (BFCirr) Thestandard deviation of BFCirr called BFCsd measures howasymmetric the departure of the actual limits of the distortionfrom the perfect circular shape of the BFC is TogetherBFCirr and BFCsd can be interpreted as the deviation ofthe actual distortion from a perfectly rotational symmetricshape The higher the value of this parameter the larger thedeviation from a circular shape and it is expressed in mmThe device has been applied in several studies to differentocular conditions showing consistency in its measurements
BioMed Research International 3
In a recent study the system has been able to differentiatethe light disturbance betweenmonofocal bifocal and trifocalpseudophakic patients (Brito et al J Cataract Refract Surg inpress)
Corneal aberrations were derived from topography dataobtained with the Oculus Easygraph (Oculus DudenhofenGermany) Corneal higher order aberrations in the form ofspherical-like coma-like and secondary astigmatism werecalculated from the Zernike coefficients provided by thetopographer for 30 45 and 60mm pupil sizes
Measurements of CSF (CSF) were carried out usinga 2210158401015840 LCD screen (Topcon CC-100XP 75-1 Hasunuma-cho Itabashi-ku Tokyo 174-8580 Japan) The frequenciestested were 150 212 300 424 600 849 1200 1697 and2400 cpd Test distance was 5m under photopic conditionsThis consisted of a total of 81 presentations (9 spatial frequen-cies at 9 different contrast levels)
Light distortion and CSF parameters were recordedmonocularly and binocularly while the subject was wearingthe best spherocylindrical overrefraction For monocularanalysis only the right eye of each subject has been consid-ered All measurements were obtained at baseline and after 17 15 and 30 days of treatment
22 Statistical Analysis Statistical analysis was carried outusing SPSS software v150 (SPSS Inc Chicago IL) Descrip-tive statistics of the variables measured in the study wereproduced Normality of data distribution was assessed withKolmogorov-Smirnov test All parameters followed a nor-mal distribution (119870-119878 119875 gt 005) Changes in differentparameters from baseline to subsequent visits were comparedusing ANOVA test with Bonferroni correction Correlationsbetween different parameters were performed with Pearsoncorrelation Statistical significance criteria were established at119875 lt 005
3 Results
31 Light Distortion Size-related light distortion parameters(LDI and BFCr) and regularity-related parameters (BFCirrand BFCsd) showed a statistically significant change overtime on ANOVA analysis (119875 lt 005) but there were no signif-icant changes from baseline to any of the subsequent analyses(Bonferroni correction for multiple comparisons) Figure 2exemplifies the variations of size-related and irregularity-related parameters of monocular and binocular light distor-tion over time Amarked and statistically significant increaseon day 1 after treatment onset has been observed
LDI index returns to baseline on day 7 and remains atbaseline level afterwards Conversely irregularity parameter(BFCirr) shows a different path displaying a significantreduction after day 7 compared to baseline after a transientincrease on day 1 Binocular analysis did not report anystatistically significant change from baseline to day 1 orsubsequent visits for LDI (119875 gt 0088) or BFCr (119875 gt 0060)
32 Corneal Aberrations There have been statistically signif-icant changes from baseline in all optical quality descriptors
of the corneal front surface for the three pupil sizes underanalysis (119875 lt 005 ANOVA with Bonferroni correction)the exception to this being secondary astigmatism for 30mmpupil on day 7 and coma-like aberrations for 60mmpupil onday 1 (119875 gt 005) Figure 3 illustrates the changes in cornealfront surface optical aberrations for different pupil sizes
33 Contrast Sensitivity Function Monocular CSF resultspresented statistically significant changes over time for fre-quencies between 300 and 2400 cpd (ANOVA 119875 lt 005)Bonferroni post hoc correction showed that there was onlya significant decrease in contrast sensitivity (CS) for frequen-cies 300 cpd to 849 cpd frombaseline to day 1 BinocularCSFpresented only statistically significant changes over time for600 cpd (119875 = 0024 ANOVA) and 2400 cpd (119875 = 0029ANOVA) (Figure 4)
34 Correlations Correlations between the outcome mea-sures (light distortion corneal higher order aberrations andCSF) were obtained after the first night of lens wear after 7days after 15 days and after 30 days It was observed thatspherical-like and coma-like aberrations were inversely cor-related with the irregularity of the light distortion (BFCirr)and the monocular CSF respectively after first night Thesecorrelations were statistically significant after the first nightof treatment for coma-like aberration with 3mm pupil (119903 =minus0414 to 119903 = minus0500 119875 lt 0001 for 12 and 24 cpd resp)Total RMS showed the higher and statistically significantcorrelation with CSF for 424 and 6 cpd after 7 days oftreatment for the 3mmpupil size (119903 = minus0529 and 119903 = minus0551119875 lt 0001) The correlations were weaker (119903 lt 0472) afterfirst night and even lower after 1 month of treatment (119903 lt0323)
At the 7 daysrsquo follow-up visit light distortion param-eters and corneal higher order aberrations were inverselycorrelated with monocular CS Size (LDI and BFCRad) andirregularity (BFCIrreg) were significantly correlated (119903 leminus0400 119875 le 0013) These correlations were even higher atthe 15 daysrsquo visit for LDI and BFCIrr with CS for 6 cpd spatialfrequency (119903 le minus0600 119875 lt 0001) Coma-like aberrationsfor 45mm pupil size were also negatively correlated withCS for 424 and 6 cpd special frequencies (119903 le minus0550119875 lt 0001) Finally after 1 month the correlations betweenlight distortion and corneal higher order aberrations withmonocular CS were smaller (119903 ge minus0300 119875 ge 0022) orabsent
4 Discussion
In the present study BCVA was maintained at baseline levelover the follow-up period Ocular higher order aberrationssignificantly increased at 1 month after the procedure andremained stable thereafter There was an initial loss in CSafter overnight OK and the loss persisted during the 1st-year follow-up As a whole all these parameters were stablethroughout the posttreatment period from 1 month to 12months That is posttreatment clinical parameters includingrefraction visual acuity corneal higher order aberrations
4 BioMed Research International
5
10
15
20
25
30
Follow-up visit
MonocularBinocular
BFC R
adiu
s(m
m)
Baseline 30 days
30 days
15 days7 days1 day
(a)
0
5
10
15
20
25
LDI (
)
BaselineFollow-up visit
Monocular
30 days15 days7 days1 day
Binocular
(b)
05
1
15
2
25
3
Follow-up visit
MonocularBinocular
BFC I
rreg
ular
ity(m
m)
Baseline 30 days15 days7 days1 day
(c)
Figure 2 Monocular and binocular Best Fit Circle Radius (BFCr) (a) Light Distortion Index (LDI) (b) and BFC Irregularity (BFCIrregularity) parameter (c) of light distortion Bars represent the Standard Error of the Mean (SEM)
and CS were stable in the eyes that underwent overnight OK[7]
CS is a fundamental feature of vision and its measure-ment provides useful information about visual function thatmay not be obtained by standard visual acuity testing [13]CS has been subject of research in other fields such asrefractive surgery showing a significant decrease soon afterthe procedure [14 15] In the short term after both OK andcorneal refractive surgery corneal higher order aberrationsincrease and CSF decreases as the first response to treatmentIn the long term it has been reported that in the case ofrefractive surgery it recovers between 3 and 12 months aftertreatment reaching values similar to baseline [16 17] Similarresults have been found after OK treatment in the presentstudy with faster recoveryThis might be related with the fact
that in OK treatment no healing processes are involved andCS is recovered once the treatment is stabilized A potentiallimitation of our study is that we are considering cornealaberrations instead of total aberrationsThis might justify theweak correlations between visual function as measured withCSF or light distortion and aberrations
The impact of OK on visual performance however hasnot been studied in detailThere are few long-termOKstudiesin which the variation of higher order aberrations and CSFare studied [11] and one short-term study [10] in which lightdistortion is measured to investigate the correlation betweenpre- and posttreatment parameters and glare scores in OKsubjects who had used OK lenses for more than 3 months
In the present longitudinal study we investigated changesin perception of light distortion changes in corneal higher
Figure 3 Optical quality of the corneal front surface for different pupil sizes represented by the root mean square (RMS) of spherical-likeaberrations (a) coma-like aberrations (b) and secondary astigmatism (c) Bars represent the Standard Error of the Mean (SEM)
order aberrations and CSF as representative of visual qualityin eyes undergoing overnight OK for one year
The analysis of light distortion surrounding a light sourcehas proved to be effective in determining the time-courseof changes in visual quality from the subjectrsquos perspectiveand irrespective of the corneal higher order aberrationspattern observed A previous study by Villa et al used asimilar methodology but based on a software platform anda computer screen which is more limited in the presentationof bright stimuli In their study they reported an increasein light disturbances after corneal refractive surgery [18]Lorente-Velazquez et al used a different methodology toevaluate the effect of OK on the intraocular retinal stray lightover a period of 1 month using the C-Quant instrument
based on the compensation-comparison method to deriveretinal stray light [19] They observed that minor changes inthe stray light were not correlated with other psychophysicalparameters as the CSF Furthermore the authors reported animprovement in retinal stray light after 1 month comparedto baseline This suggests that stray light does not reflectthe impact of aberrations or any optical defects other thanchanges in the transparency of tissues Similarly Cervinoet al were not able to find any significant effect of LASIKsurgery on stray light values obtained with the C-Quant [20]while the analysis of halo size with a software system showedsignificant changes as others had previously found [18]Again this supports the assumption that the light distortionreported here is not related to stray light phenomena
Figure 4 Monocular (a) and binocular (b) log contrast sensitivity (CS) Bars represent the Standard Error of the Mean (SEM) only for visitson days 1 and 30 the remaining error bars are omitted for clarity
We observed an inverse correlation between coma-likeaberrations and CSF for medium and higher spatial fre-quencies which might be related to the relatively frequentdecentration and irregularity of the treatment zone after thefirst night wearing CL Our results showed no significant cor-relation between the different optical (corneal aberrations)and quality of vision (CSF and light distortion) parameters atthe end of the month The absence of significant correlationsat this stage might be interpreted as a neural adaptationprocess that is independent of the optical quality of thecornea A hypothetical component of this neural adaptationmight even take place at the retinal level with a change inthe apodization mechanism of the photoreceptors such thatthey overcome the effects of deteriorated peripheral opticsof the eye and take advantage of the relatively unchangedoptical quality within the more central part of the pupil Infact our results agree with previous reports by our group[5] that showed that the increase in corneal aberrations ishardly significant for a pupil size of 3mm or less whatmight explain visual quality remaining within normal limitsin the midterm despite the initial deterioration In anotherstudy analyzing subjective responses versus light distortionperception (whether it increases decreases or remains thesame) we found that after 1 year of treatment 421 reported adecrease and the remaining 579 reported that the subjectivefeeling of light distortion remained the same [8] In thepresent study light distortion analysis showed a transientincrease followed by a reduction to baseline levels after 7days of treatment This is in agreement with the clinicalobservation of adaptation to the distortion effect observedin our previous study [8] Similarly McAlinden et al usingthe Quality of Vision Questionnaire (QoV) [21] reported
a transient worsening of the subjective perception of qualityof vision that returned to baseline a few weeks after laser-assisted subepithelial keratectomy [22] Again the resultsof the QoV questionnaires after surgery showed a slowerrecovery which might be related with the healing processesoccurring in the cornea which are not present in the OKtreatment
Interestingly we observed a decrease in the distortionparameters related to the irregularity of the light distortionThis might be explained by the spherical aberration inducedthat leads to a more uniform and more radially symmetricdistortion pattern compared to baseline which will resultin a reduction of the irregularities in the form of spikessurrounding the light source Regarding aberration changesin the anterior corneal surface an average increase of 110for 30mm pupil to 233 for 60mm pupil in the spherical-like RMS was observed Changes in comatic aberration wereless severe and more similar for different pupil sizes rangingfrom 108 to 150 for 30 and 60mm pupil sizes Secondaryastigmatism showed a marked increase ranging from 62 to195 for 30 and 60mm pupil sizes Similar values have beenreported by other studies [5 6 23]
To our knowledge this is the first study addressing theshort-term changes in the optical quality of the anteriorcorneal surface and the visual quality determined by meansof monocular and binocular CSF and light distortion mea-surement Although the light distortion andCSF recovered tobaseline values the lack of correlation after 15 days betweenlight distortion andCSFmight confirm that bothmethods aremeasuring different aspects of visual quality
In summary we have shown that despite the reductionin optical quality of the anterior corneal surface some of the
BioMed Research International 7
parameters related to visual quality of the eye return to beingwithin normal range values within a narrow period of timeand this might be related with a neural adaptation process
Conflict of Interests
The authors have no proprietary interest in any of theinstruments or materials mentioned in this paper
Acknowledgments
This research was supported in part by Projects PTDCSAU-BEB0983912008FCOMP-01-0124-FEDER-010897 andPTDCSAU-BEB0983922008FCOMP-01-0124-FEDER-010898 The present work was presented in part at theCIOCV2012 conference (Braga April 9-10 2011)
References
[1] F Lu T Simpson L Sorbara and D Fonn ldquoCorneal refractivetherapy with different lens materials part 2 effect of oxygentransmissibility on corneal shape and optical characteristicsrdquoOptometry amp Vision Science vol 84 pp 349ndash356 2007
[2] A Queiros J M Gonzalez-Meijome C Villa-Collar A RGutierrez and J Jorge ldquoLocal steepening in peripheral cornealcurvature after corneal refractive therapy and LASIKrdquo Optom-etry and Vision Science vol 87 no 6 pp 432ndash439 2010
[3] S Haque D Fonn T Simpson and L Jones ldquoCorneal andepithelial thickness changes after 4 weeks of overnight cornealrefractive therapy lens wear measured with optical coherencetomographyrdquo Eye and Contact Lens vol 30 no 4 pp 189ndash1932004
[4] S Haque D Fonn T Simpson and L Jones ldquoCorneal refractivetherapy with different lens materials Part 1 corneal stromaland epithelial thickness changesrdquoOptometry andVision Sciencevol 84 no 4 pp 343ndash348 2007
[5] T Hiraoka Y Matsumoto F Okamoto et al ldquoCorneal higher-order aberrations induced by overnight orthokeratologyrdquoAmerican Journal of Ophthalmology vol 139 no 3 pp 429ndash4362005
[6] A Queiros C Villa-Collar J M Gonzalez-Meijome J Jorgeand A R Gutierrez ldquoEffect of pupil size on corneal aberrationsbefore and after standard laser in situ keratomileusis customlaser in situ keratomileusis and corneal refractive therapyrdquoTheAmerican Journal of Ophthalmology vol 150 no 1 pp 97e1ndash109e1 2010
[7] F Lu T Simpson L Sorbara and D Fonn ldquoThe relationshipbetween the treatment zone diameter and visual optical andsubjective performance in Corneal Refractive Therapy lenswearersrdquoOphthalmic and Physiological Optics vol 27 no 6 pp568ndash578 2007
[8] E Santolaria A Cervino A Queiros R Brautaset and JM Gonzalez-Meijome ldquoSubjective satisfaction in long-termorthokeratology patientsrdquo Eye and Contact Lens vol 39 no 6pp 388ndash393 2013
[9] A Queiros C Villa-Collar A R Gutierrez J Jorge and JM Gonzalez-Meijome ldquoQuality of life of myopic subjects withdifferent methods of visual correction using the NEI RQL-42questionnairerdquo Eye and Contact Lens vol 38 no 2 pp 116ndash1212012
[10] T Kojima A Hasegawa S Hara et al ldquoQuantitative evaluationof night vision and correlation of refractive and topographicalparameters with glare after orthokeratologyrdquoGraefersquos Archive forClinical and Experimental Ophthalmology vol 249 no 10 pp1519ndash1526 2011
[11] T Hiraoka C Okamoto Y Ishii T Kakita F Okamoto and TOshika ldquoTime course of changes in ocular higher-order aber-rations and contrast sensitivity after overnight orthokeratologyrdquoInvestigative Ophthalmology and Visual Science vol 49 no 10pp 4314ndash4320 2008
[12] J M M Linhares H Neves D Lopes-Ferreira M Faria-Ribeiro S C Peixoto-de-Matos and J M Gonzalez-MeijomeldquoRadiometric characterization of a novel LED array system forvisual assessmentrdquo Journal of Modern Optics vol 60 no 14 pp1136ndash1144 2013
[13] K Pesudovs C A Hazel R M L Doran and D B ElliottldquoThe usefulness of Vistech and FACT contrast sensitivity chartsfor cataract and refractive surgery outcomes researchrdquo BritishJournal of Ophthalmology vol 88 no 1 pp 11ndash16 2004
[14] J T Holladay D R Dudeja and J Chang ldquoFunctionalvision and corneal changes after laser in situ keratomileusisdetermined by contrast sensitivity glare testing and cornealtopographyrdquo Journal of Cataract and Refractive Surgery vol 25no 5 pp 663ndash669 1999
[15] N Yamane K Miyata T Samejima et al ldquoOcular higher-order aberrations and contrast sensitivity after conventionallaser in situ keratomileusisrdquo Investigative Ophthalmology andVisual Science vol 45 no 11 pp 3986ndash3990 2004
[16] S Mutyala M B McDonald K A Scheinblum M D OstrickS F Brint and H Thompson ldquoContrast sensitivity evaluationafter laser in situ keratomileusisrdquo Ophthalmology vol 107 no10 pp 1864ndash1867 2000
[17] J W W Chan M H Edwards G C Woo and V C P WooldquoContrast sensitivity after laser in situ keratomileusis one-yearfollow-uprdquo Journal of Cataract and Refractive Surgery vol 28no 10 pp 1774ndash1779 2002
[18] C Villa R Gutierrez J R Jimenez and J M Gonzalez-Meijome ldquoNight vision disturbances after successful LASIKsurgeryrdquo British Journal of Ophthalmology vol 91 no 8 pp1031ndash1037 2007
[19] A Lorente-Velazquez A Nieto-Bona C V Collar and A GMesa ldquoStraylight and contrast sensitivity after corneal refractivetherapyrdquoOptometry and Vision Science vol 88 no 10 pp 1245ndash1251 2011
[20] A Cervino C Villa-Collar J M Gonzalez-Meijome T Ferrer-Blasco and S Garcıa-Lazaro ldquoRetinal straylight and lightdistortion phenomena in normal and post-LASIK eyesrdquoGraefersquosArchive for Clinical and Experimental Ophthalmology vol 249no 10 pp 1561ndash1566 2011
[21] C McAlinden K Pesudovs and J E Moore ldquoThe developmentof an instrument to measure quality of vision the quality ofvision (QoV) questionnairerdquo Investigative Ophthalmology andVisual Science vol 51 no 11 pp 5537ndash5545 2010
[22] C McAlinden E Skiadaresi and J E Moore ldquoVisual andrefractive outcomes following myopic laser-assisted subepithe-lial keratectomy with a flying-spot excimer laserrdquo Journal ofCataract and Refractive Surgery vol 37 no 5 pp 901ndash906 2011
[23] THiraoka COkamoto Y Ishii T Kakita andTOshika ldquoCon-trast sensitivity function and ocular higher-order aberrationsfollowing overnight orthokeratologyrdquo Investigative Ophthalmol-ogy and Visual Science vol 48 no 2 pp 550ndash556 2007
with the aberrations of the anterior corneal surface andcontrast sensitivity function (CSF) over the first month oftreatment
2 Methods
A total of 29 neophyte subjects were recruited and fittedwith OK lenses for myopia correction with reverse geometryrigid gas permeable CL Inclusion criteria required that theybe over 18 years of age have less than 100 diopters (D)of refractive astigmatism be free of ocular disease haveno contraindication for overnight CL wear and present abest spectacle corrected monocular visual acuity of 090decimal (2025) or better Subjects were followed up and theywore their lenses successfully for 1 month Demographic andrefractive data of subjects are presented inTable 1 All subjectsenrolled achieved a satisfactory correction and no dropoutswere observed during the 1-month follow-up time
Subjects were informed of the purpose of the study andsigned a consent form after all their questions were answeredfollowing the tenets of the Declaration of Helsinki Subjectsunderwent a comprehensive optometric examination prior toenrollment
21 Outcome Measures Visual acuity was measured underphotopic conditions at 5m using a decimal scale chartSubjective baseline refraction and refraction at the time ofdata collection were determined as the spherocylindricalcombination that rendered the best distance visual acuitywith the highest positive power
Light distortion was analysed with an experimental pro-totype consisting of a central light emitting diode (LED)surrounded by 240 small LED sources distributed in 24semimeridians with an angular separation of 15∘ For the pur-pose of the present experiment an angular separation of 30∘was considered Figure 1 represents the arrangement of thecentral white LEDs and the surrounding smaller white LEDsThe central LED was a commercially available white LEDfrom Agilent Technologies (ref HLMP-CW47-RU000 fromAgilent Technologies Inc Berkshire United Kingdom) thesurrounding LEDs were commercially available white LEDsfrom Avago Technologies (ref HSMW-CL25 from AvagoTechnologies San Jose California United States)The subjectwas at a distance of 20m in a darkened room The physical(electronic board) display device is connected to a centralcontrol device (PC) via USB connection when heshe candetect a peripheral LED as this is moving from the innerpart to the outer part of the area of examination The subjectbeing evaluated provides feedback to the system througha remote response device (PC mouse) Peripheral stimuliare presented around the central source of light from theinner to the outer part of the field at random times rangingfrom 250 to 750 milliseconds Semimeridians are exploredin random order When the subject sees the stimulus heshepresses the mouse control and the system presents the nextsemimeridian Further description of the device can be foundelsewhere [12] After data collection and storage a softwaretool then calculates three indices that determine the size and
Table 1 Demographic refractive and keratometric data of subjects(mean plusmn SD) and range (minimum and maximum)
Age 2234 plusmn 808 years (18ndash43)Sample (malefemale ratio) 29 subjects (623)M (baseline) minus210 plusmn 093D (minus100 to minus475)J0 (baseline) minus003 plusmn 014D (minus050 to 046)J45 (baseline) 000 plusmn 008D (minus029 to 036)Flattest keratometric radius 778 plusmn 028mm (720 to 864)Steepest keratometric radius 755 plusmn 029mm (692 to 852)Decimal VA (monocular) 116 plusmn 009 (090 to 150)
Figure 1 Distribution of main central source of light and peripheralstimuli
regularity of the distortion surrounding the central source oflight
The Best Fit Circle Radius (BFCr) is defined as the circlethat best fits the distortion area resulting from the linearbinding of all points in each meridian of the device Thisparameter is expressed in mm and is linearly related to theDistortion Index (LDI) parameter
LDI is calculated as the ratio of the area or points missedby the subject and the total area explored and is expressed asa percentage () The higher values of distortion (BFCr andLDI) are interpreted as a lower ability to discriminate smallstimuli surrounding the central light source
The irregularity of the distortion area is derived as thedeviation of the actual polygonal shape obtained from theBFC fit and is called the BFC Irregularity (BFCirr) Thestandard deviation of BFCirr called BFCsd measures howasymmetric the departure of the actual limits of the distortionfrom the perfect circular shape of the BFC is TogetherBFCirr and BFCsd can be interpreted as the deviation ofthe actual distortion from a perfectly rotational symmetricshape The higher the value of this parameter the larger thedeviation from a circular shape and it is expressed in mmThe device has been applied in several studies to differentocular conditions showing consistency in its measurements
BioMed Research International 3
In a recent study the system has been able to differentiatethe light disturbance betweenmonofocal bifocal and trifocalpseudophakic patients (Brito et al J Cataract Refract Surg inpress)
Corneal aberrations were derived from topography dataobtained with the Oculus Easygraph (Oculus DudenhofenGermany) Corneal higher order aberrations in the form ofspherical-like coma-like and secondary astigmatism werecalculated from the Zernike coefficients provided by thetopographer for 30 45 and 60mm pupil sizes
Measurements of CSF (CSF) were carried out usinga 2210158401015840 LCD screen (Topcon CC-100XP 75-1 Hasunuma-cho Itabashi-ku Tokyo 174-8580 Japan) The frequenciestested were 150 212 300 424 600 849 1200 1697 and2400 cpd Test distance was 5m under photopic conditionsThis consisted of a total of 81 presentations (9 spatial frequen-cies at 9 different contrast levels)
Light distortion and CSF parameters were recordedmonocularly and binocularly while the subject was wearingthe best spherocylindrical overrefraction For monocularanalysis only the right eye of each subject has been consid-ered All measurements were obtained at baseline and after 17 15 and 30 days of treatment
22 Statistical Analysis Statistical analysis was carried outusing SPSS software v150 (SPSS Inc Chicago IL) Descrip-tive statistics of the variables measured in the study wereproduced Normality of data distribution was assessed withKolmogorov-Smirnov test All parameters followed a nor-mal distribution (119870-119878 119875 gt 005) Changes in differentparameters from baseline to subsequent visits were comparedusing ANOVA test with Bonferroni correction Correlationsbetween different parameters were performed with Pearsoncorrelation Statistical significance criteria were established at119875 lt 005
3 Results
31 Light Distortion Size-related light distortion parameters(LDI and BFCr) and regularity-related parameters (BFCirrand BFCsd) showed a statistically significant change overtime on ANOVA analysis (119875 lt 005) but there were no signif-icant changes from baseline to any of the subsequent analyses(Bonferroni correction for multiple comparisons) Figure 2exemplifies the variations of size-related and irregularity-related parameters of monocular and binocular light distor-tion over time Amarked and statistically significant increaseon day 1 after treatment onset has been observed
LDI index returns to baseline on day 7 and remains atbaseline level afterwards Conversely irregularity parameter(BFCirr) shows a different path displaying a significantreduction after day 7 compared to baseline after a transientincrease on day 1 Binocular analysis did not report anystatistically significant change from baseline to day 1 orsubsequent visits for LDI (119875 gt 0088) or BFCr (119875 gt 0060)
32 Corneal Aberrations There have been statistically signif-icant changes from baseline in all optical quality descriptors
of the corneal front surface for the three pupil sizes underanalysis (119875 lt 005 ANOVA with Bonferroni correction)the exception to this being secondary astigmatism for 30mmpupil on day 7 and coma-like aberrations for 60mmpupil onday 1 (119875 gt 005) Figure 3 illustrates the changes in cornealfront surface optical aberrations for different pupil sizes
33 Contrast Sensitivity Function Monocular CSF resultspresented statistically significant changes over time for fre-quencies between 300 and 2400 cpd (ANOVA 119875 lt 005)Bonferroni post hoc correction showed that there was onlya significant decrease in contrast sensitivity (CS) for frequen-cies 300 cpd to 849 cpd frombaseline to day 1 BinocularCSFpresented only statistically significant changes over time for600 cpd (119875 = 0024 ANOVA) and 2400 cpd (119875 = 0029ANOVA) (Figure 4)
34 Correlations Correlations between the outcome mea-sures (light distortion corneal higher order aberrations andCSF) were obtained after the first night of lens wear after 7days after 15 days and after 30 days It was observed thatspherical-like and coma-like aberrations were inversely cor-related with the irregularity of the light distortion (BFCirr)and the monocular CSF respectively after first night Thesecorrelations were statistically significant after the first nightof treatment for coma-like aberration with 3mm pupil (119903 =minus0414 to 119903 = minus0500 119875 lt 0001 for 12 and 24 cpd resp)Total RMS showed the higher and statistically significantcorrelation with CSF for 424 and 6 cpd after 7 days oftreatment for the 3mmpupil size (119903 = minus0529 and 119903 = minus0551119875 lt 0001) The correlations were weaker (119903 lt 0472) afterfirst night and even lower after 1 month of treatment (119903 lt0323)
At the 7 daysrsquo follow-up visit light distortion param-eters and corneal higher order aberrations were inverselycorrelated with monocular CS Size (LDI and BFCRad) andirregularity (BFCIrreg) were significantly correlated (119903 leminus0400 119875 le 0013) These correlations were even higher atthe 15 daysrsquo visit for LDI and BFCIrr with CS for 6 cpd spatialfrequency (119903 le minus0600 119875 lt 0001) Coma-like aberrationsfor 45mm pupil size were also negatively correlated withCS for 424 and 6 cpd special frequencies (119903 le minus0550119875 lt 0001) Finally after 1 month the correlations betweenlight distortion and corneal higher order aberrations withmonocular CS were smaller (119903 ge minus0300 119875 ge 0022) orabsent
4 Discussion
In the present study BCVA was maintained at baseline levelover the follow-up period Ocular higher order aberrationssignificantly increased at 1 month after the procedure andremained stable thereafter There was an initial loss in CSafter overnight OK and the loss persisted during the 1st-year follow-up As a whole all these parameters were stablethroughout the posttreatment period from 1 month to 12months That is posttreatment clinical parameters includingrefraction visual acuity corneal higher order aberrations
4 BioMed Research International
5
10
15
20
25
30
Follow-up visit
MonocularBinocular
BFC R
adiu
s(m
m)
Baseline 30 days
30 days
15 days7 days1 day
(a)
0
5
10
15
20
25
LDI (
)
BaselineFollow-up visit
Monocular
30 days15 days7 days1 day
Binocular
(b)
05
1
15
2
25
3
Follow-up visit
MonocularBinocular
BFC I
rreg
ular
ity(m
m)
Baseline 30 days15 days7 days1 day
(c)
Figure 2 Monocular and binocular Best Fit Circle Radius (BFCr) (a) Light Distortion Index (LDI) (b) and BFC Irregularity (BFCIrregularity) parameter (c) of light distortion Bars represent the Standard Error of the Mean (SEM)
and CS were stable in the eyes that underwent overnight OK[7]
CS is a fundamental feature of vision and its measure-ment provides useful information about visual function thatmay not be obtained by standard visual acuity testing [13]CS has been subject of research in other fields such asrefractive surgery showing a significant decrease soon afterthe procedure [14 15] In the short term after both OK andcorneal refractive surgery corneal higher order aberrationsincrease and CSF decreases as the first response to treatmentIn the long term it has been reported that in the case ofrefractive surgery it recovers between 3 and 12 months aftertreatment reaching values similar to baseline [16 17] Similarresults have been found after OK treatment in the presentstudy with faster recoveryThis might be related with the fact
that in OK treatment no healing processes are involved andCS is recovered once the treatment is stabilized A potentiallimitation of our study is that we are considering cornealaberrations instead of total aberrationsThis might justify theweak correlations between visual function as measured withCSF or light distortion and aberrations
The impact of OK on visual performance however hasnot been studied in detailThere are few long-termOKstudiesin which the variation of higher order aberrations and CSFare studied [11] and one short-term study [10] in which lightdistortion is measured to investigate the correlation betweenpre- and posttreatment parameters and glare scores in OKsubjects who had used OK lenses for more than 3 months
In the present longitudinal study we investigated changesin perception of light distortion changes in corneal higher
Figure 3 Optical quality of the corneal front surface for different pupil sizes represented by the root mean square (RMS) of spherical-likeaberrations (a) coma-like aberrations (b) and secondary astigmatism (c) Bars represent the Standard Error of the Mean (SEM)
order aberrations and CSF as representative of visual qualityin eyes undergoing overnight OK for one year
The analysis of light distortion surrounding a light sourcehas proved to be effective in determining the time-courseof changes in visual quality from the subjectrsquos perspectiveand irrespective of the corneal higher order aberrationspattern observed A previous study by Villa et al used asimilar methodology but based on a software platform anda computer screen which is more limited in the presentationof bright stimuli In their study they reported an increasein light disturbances after corneal refractive surgery [18]Lorente-Velazquez et al used a different methodology toevaluate the effect of OK on the intraocular retinal stray lightover a period of 1 month using the C-Quant instrument
based on the compensation-comparison method to deriveretinal stray light [19] They observed that minor changes inthe stray light were not correlated with other psychophysicalparameters as the CSF Furthermore the authors reported animprovement in retinal stray light after 1 month comparedto baseline This suggests that stray light does not reflectthe impact of aberrations or any optical defects other thanchanges in the transparency of tissues Similarly Cervinoet al were not able to find any significant effect of LASIKsurgery on stray light values obtained with the C-Quant [20]while the analysis of halo size with a software system showedsignificant changes as others had previously found [18]Again this supports the assumption that the light distortionreported here is not related to stray light phenomena
Figure 4 Monocular (a) and binocular (b) log contrast sensitivity (CS) Bars represent the Standard Error of the Mean (SEM) only for visitson days 1 and 30 the remaining error bars are omitted for clarity
We observed an inverse correlation between coma-likeaberrations and CSF for medium and higher spatial fre-quencies which might be related to the relatively frequentdecentration and irregularity of the treatment zone after thefirst night wearing CL Our results showed no significant cor-relation between the different optical (corneal aberrations)and quality of vision (CSF and light distortion) parameters atthe end of the month The absence of significant correlationsat this stage might be interpreted as a neural adaptationprocess that is independent of the optical quality of thecornea A hypothetical component of this neural adaptationmight even take place at the retinal level with a change inthe apodization mechanism of the photoreceptors such thatthey overcome the effects of deteriorated peripheral opticsof the eye and take advantage of the relatively unchangedoptical quality within the more central part of the pupil Infact our results agree with previous reports by our group[5] that showed that the increase in corneal aberrations ishardly significant for a pupil size of 3mm or less whatmight explain visual quality remaining within normal limitsin the midterm despite the initial deterioration In anotherstudy analyzing subjective responses versus light distortionperception (whether it increases decreases or remains thesame) we found that after 1 year of treatment 421 reported adecrease and the remaining 579 reported that the subjectivefeeling of light distortion remained the same [8] In thepresent study light distortion analysis showed a transientincrease followed by a reduction to baseline levels after 7days of treatment This is in agreement with the clinicalobservation of adaptation to the distortion effect observedin our previous study [8] Similarly McAlinden et al usingthe Quality of Vision Questionnaire (QoV) [21] reported
a transient worsening of the subjective perception of qualityof vision that returned to baseline a few weeks after laser-assisted subepithelial keratectomy [22] Again the resultsof the QoV questionnaires after surgery showed a slowerrecovery which might be related with the healing processesoccurring in the cornea which are not present in the OKtreatment
Interestingly we observed a decrease in the distortionparameters related to the irregularity of the light distortionThis might be explained by the spherical aberration inducedthat leads to a more uniform and more radially symmetricdistortion pattern compared to baseline which will resultin a reduction of the irregularities in the form of spikessurrounding the light source Regarding aberration changesin the anterior corneal surface an average increase of 110for 30mm pupil to 233 for 60mm pupil in the spherical-like RMS was observed Changes in comatic aberration wereless severe and more similar for different pupil sizes rangingfrom 108 to 150 for 30 and 60mm pupil sizes Secondaryastigmatism showed a marked increase ranging from 62 to195 for 30 and 60mm pupil sizes Similar values have beenreported by other studies [5 6 23]
To our knowledge this is the first study addressing theshort-term changes in the optical quality of the anteriorcorneal surface and the visual quality determined by meansof monocular and binocular CSF and light distortion mea-surement Although the light distortion andCSF recovered tobaseline values the lack of correlation after 15 days betweenlight distortion andCSFmight confirm that bothmethods aremeasuring different aspects of visual quality
In summary we have shown that despite the reductionin optical quality of the anterior corneal surface some of the
BioMed Research International 7
parameters related to visual quality of the eye return to beingwithin normal range values within a narrow period of timeand this might be related with a neural adaptation process
Conflict of Interests
The authors have no proprietary interest in any of theinstruments or materials mentioned in this paper
Acknowledgments
This research was supported in part by Projects PTDCSAU-BEB0983912008FCOMP-01-0124-FEDER-010897 andPTDCSAU-BEB0983922008FCOMP-01-0124-FEDER-010898 The present work was presented in part at theCIOCV2012 conference (Braga April 9-10 2011)
References
[1] F Lu T Simpson L Sorbara and D Fonn ldquoCorneal refractivetherapy with different lens materials part 2 effect of oxygentransmissibility on corneal shape and optical characteristicsrdquoOptometry amp Vision Science vol 84 pp 349ndash356 2007
[2] A Queiros J M Gonzalez-Meijome C Villa-Collar A RGutierrez and J Jorge ldquoLocal steepening in peripheral cornealcurvature after corneal refractive therapy and LASIKrdquo Optom-etry and Vision Science vol 87 no 6 pp 432ndash439 2010
[3] S Haque D Fonn T Simpson and L Jones ldquoCorneal andepithelial thickness changes after 4 weeks of overnight cornealrefractive therapy lens wear measured with optical coherencetomographyrdquo Eye and Contact Lens vol 30 no 4 pp 189ndash1932004
[4] S Haque D Fonn T Simpson and L Jones ldquoCorneal refractivetherapy with different lens materials Part 1 corneal stromaland epithelial thickness changesrdquoOptometry andVision Sciencevol 84 no 4 pp 343ndash348 2007
[5] T Hiraoka Y Matsumoto F Okamoto et al ldquoCorneal higher-order aberrations induced by overnight orthokeratologyrdquoAmerican Journal of Ophthalmology vol 139 no 3 pp 429ndash4362005
[6] A Queiros C Villa-Collar J M Gonzalez-Meijome J Jorgeand A R Gutierrez ldquoEffect of pupil size on corneal aberrationsbefore and after standard laser in situ keratomileusis customlaser in situ keratomileusis and corneal refractive therapyrdquoTheAmerican Journal of Ophthalmology vol 150 no 1 pp 97e1ndash109e1 2010
[7] F Lu T Simpson L Sorbara and D Fonn ldquoThe relationshipbetween the treatment zone diameter and visual optical andsubjective performance in Corneal Refractive Therapy lenswearersrdquoOphthalmic and Physiological Optics vol 27 no 6 pp568ndash578 2007
[8] E Santolaria A Cervino A Queiros R Brautaset and JM Gonzalez-Meijome ldquoSubjective satisfaction in long-termorthokeratology patientsrdquo Eye and Contact Lens vol 39 no 6pp 388ndash393 2013
[9] A Queiros C Villa-Collar A R Gutierrez J Jorge and JM Gonzalez-Meijome ldquoQuality of life of myopic subjects withdifferent methods of visual correction using the NEI RQL-42questionnairerdquo Eye and Contact Lens vol 38 no 2 pp 116ndash1212012
[10] T Kojima A Hasegawa S Hara et al ldquoQuantitative evaluationof night vision and correlation of refractive and topographicalparameters with glare after orthokeratologyrdquoGraefersquos Archive forClinical and Experimental Ophthalmology vol 249 no 10 pp1519ndash1526 2011
[11] T Hiraoka C Okamoto Y Ishii T Kakita F Okamoto and TOshika ldquoTime course of changes in ocular higher-order aber-rations and contrast sensitivity after overnight orthokeratologyrdquoInvestigative Ophthalmology and Visual Science vol 49 no 10pp 4314ndash4320 2008
[12] J M M Linhares H Neves D Lopes-Ferreira M Faria-Ribeiro S C Peixoto-de-Matos and J M Gonzalez-MeijomeldquoRadiometric characterization of a novel LED array system forvisual assessmentrdquo Journal of Modern Optics vol 60 no 14 pp1136ndash1144 2013
[13] K Pesudovs C A Hazel R M L Doran and D B ElliottldquoThe usefulness of Vistech and FACT contrast sensitivity chartsfor cataract and refractive surgery outcomes researchrdquo BritishJournal of Ophthalmology vol 88 no 1 pp 11ndash16 2004
[14] J T Holladay D R Dudeja and J Chang ldquoFunctionalvision and corneal changes after laser in situ keratomileusisdetermined by contrast sensitivity glare testing and cornealtopographyrdquo Journal of Cataract and Refractive Surgery vol 25no 5 pp 663ndash669 1999
[15] N Yamane K Miyata T Samejima et al ldquoOcular higher-order aberrations and contrast sensitivity after conventionallaser in situ keratomileusisrdquo Investigative Ophthalmology andVisual Science vol 45 no 11 pp 3986ndash3990 2004
[16] S Mutyala M B McDonald K A Scheinblum M D OstrickS F Brint and H Thompson ldquoContrast sensitivity evaluationafter laser in situ keratomileusisrdquo Ophthalmology vol 107 no10 pp 1864ndash1867 2000
[17] J W W Chan M H Edwards G C Woo and V C P WooldquoContrast sensitivity after laser in situ keratomileusis one-yearfollow-uprdquo Journal of Cataract and Refractive Surgery vol 28no 10 pp 1774ndash1779 2002
[18] C Villa R Gutierrez J R Jimenez and J M Gonzalez-Meijome ldquoNight vision disturbances after successful LASIKsurgeryrdquo British Journal of Ophthalmology vol 91 no 8 pp1031ndash1037 2007
[19] A Lorente-Velazquez A Nieto-Bona C V Collar and A GMesa ldquoStraylight and contrast sensitivity after corneal refractivetherapyrdquoOptometry and Vision Science vol 88 no 10 pp 1245ndash1251 2011
[20] A Cervino C Villa-Collar J M Gonzalez-Meijome T Ferrer-Blasco and S Garcıa-Lazaro ldquoRetinal straylight and lightdistortion phenomena in normal and post-LASIK eyesrdquoGraefersquosArchive for Clinical and Experimental Ophthalmology vol 249no 10 pp 1561ndash1566 2011
[21] C McAlinden K Pesudovs and J E Moore ldquoThe developmentof an instrument to measure quality of vision the quality ofvision (QoV) questionnairerdquo Investigative Ophthalmology andVisual Science vol 51 no 11 pp 5537ndash5545 2010
[22] C McAlinden E Skiadaresi and J E Moore ldquoVisual andrefractive outcomes following myopic laser-assisted subepithe-lial keratectomy with a flying-spot excimer laserrdquo Journal ofCataract and Refractive Surgery vol 37 no 5 pp 901ndash906 2011
[23] THiraoka COkamoto Y Ishii T Kakita andTOshika ldquoCon-trast sensitivity function and ocular higher-order aberrationsfollowing overnight orthokeratologyrdquo Investigative Ophthalmol-ogy and Visual Science vol 48 no 2 pp 550ndash556 2007
In a recent study the system has been able to differentiatethe light disturbance betweenmonofocal bifocal and trifocalpseudophakic patients (Brito et al J Cataract Refract Surg inpress)
Corneal aberrations were derived from topography dataobtained with the Oculus Easygraph (Oculus DudenhofenGermany) Corneal higher order aberrations in the form ofspherical-like coma-like and secondary astigmatism werecalculated from the Zernike coefficients provided by thetopographer for 30 45 and 60mm pupil sizes
Measurements of CSF (CSF) were carried out usinga 2210158401015840 LCD screen (Topcon CC-100XP 75-1 Hasunuma-cho Itabashi-ku Tokyo 174-8580 Japan) The frequenciestested were 150 212 300 424 600 849 1200 1697 and2400 cpd Test distance was 5m under photopic conditionsThis consisted of a total of 81 presentations (9 spatial frequen-cies at 9 different contrast levels)
Light distortion and CSF parameters were recordedmonocularly and binocularly while the subject was wearingthe best spherocylindrical overrefraction For monocularanalysis only the right eye of each subject has been consid-ered All measurements were obtained at baseline and after 17 15 and 30 days of treatment
22 Statistical Analysis Statistical analysis was carried outusing SPSS software v150 (SPSS Inc Chicago IL) Descrip-tive statistics of the variables measured in the study wereproduced Normality of data distribution was assessed withKolmogorov-Smirnov test All parameters followed a nor-mal distribution (119870-119878 119875 gt 005) Changes in differentparameters from baseline to subsequent visits were comparedusing ANOVA test with Bonferroni correction Correlationsbetween different parameters were performed with Pearsoncorrelation Statistical significance criteria were established at119875 lt 005
3 Results
31 Light Distortion Size-related light distortion parameters(LDI and BFCr) and regularity-related parameters (BFCirrand BFCsd) showed a statistically significant change overtime on ANOVA analysis (119875 lt 005) but there were no signif-icant changes from baseline to any of the subsequent analyses(Bonferroni correction for multiple comparisons) Figure 2exemplifies the variations of size-related and irregularity-related parameters of monocular and binocular light distor-tion over time Amarked and statistically significant increaseon day 1 after treatment onset has been observed
LDI index returns to baseline on day 7 and remains atbaseline level afterwards Conversely irregularity parameter(BFCirr) shows a different path displaying a significantreduction after day 7 compared to baseline after a transientincrease on day 1 Binocular analysis did not report anystatistically significant change from baseline to day 1 orsubsequent visits for LDI (119875 gt 0088) or BFCr (119875 gt 0060)
32 Corneal Aberrations There have been statistically signif-icant changes from baseline in all optical quality descriptors
of the corneal front surface for the three pupil sizes underanalysis (119875 lt 005 ANOVA with Bonferroni correction)the exception to this being secondary astigmatism for 30mmpupil on day 7 and coma-like aberrations for 60mmpupil onday 1 (119875 gt 005) Figure 3 illustrates the changes in cornealfront surface optical aberrations for different pupil sizes
33 Contrast Sensitivity Function Monocular CSF resultspresented statistically significant changes over time for fre-quencies between 300 and 2400 cpd (ANOVA 119875 lt 005)Bonferroni post hoc correction showed that there was onlya significant decrease in contrast sensitivity (CS) for frequen-cies 300 cpd to 849 cpd frombaseline to day 1 BinocularCSFpresented only statistically significant changes over time for600 cpd (119875 = 0024 ANOVA) and 2400 cpd (119875 = 0029ANOVA) (Figure 4)
34 Correlations Correlations between the outcome mea-sures (light distortion corneal higher order aberrations andCSF) were obtained after the first night of lens wear after 7days after 15 days and after 30 days It was observed thatspherical-like and coma-like aberrations were inversely cor-related with the irregularity of the light distortion (BFCirr)and the monocular CSF respectively after first night Thesecorrelations were statistically significant after the first nightof treatment for coma-like aberration with 3mm pupil (119903 =minus0414 to 119903 = minus0500 119875 lt 0001 for 12 and 24 cpd resp)Total RMS showed the higher and statistically significantcorrelation with CSF for 424 and 6 cpd after 7 days oftreatment for the 3mmpupil size (119903 = minus0529 and 119903 = minus0551119875 lt 0001) The correlations were weaker (119903 lt 0472) afterfirst night and even lower after 1 month of treatment (119903 lt0323)
At the 7 daysrsquo follow-up visit light distortion param-eters and corneal higher order aberrations were inverselycorrelated with monocular CS Size (LDI and BFCRad) andirregularity (BFCIrreg) were significantly correlated (119903 leminus0400 119875 le 0013) These correlations were even higher atthe 15 daysrsquo visit for LDI and BFCIrr with CS for 6 cpd spatialfrequency (119903 le minus0600 119875 lt 0001) Coma-like aberrationsfor 45mm pupil size were also negatively correlated withCS for 424 and 6 cpd special frequencies (119903 le minus0550119875 lt 0001) Finally after 1 month the correlations betweenlight distortion and corneal higher order aberrations withmonocular CS were smaller (119903 ge minus0300 119875 ge 0022) orabsent
4 Discussion
In the present study BCVA was maintained at baseline levelover the follow-up period Ocular higher order aberrationssignificantly increased at 1 month after the procedure andremained stable thereafter There was an initial loss in CSafter overnight OK and the loss persisted during the 1st-year follow-up As a whole all these parameters were stablethroughout the posttreatment period from 1 month to 12months That is posttreatment clinical parameters includingrefraction visual acuity corneal higher order aberrations
4 BioMed Research International
5
10
15
20
25
30
Follow-up visit
MonocularBinocular
BFC R
adiu
s(m
m)
Baseline 30 days
30 days
15 days7 days1 day
(a)
0
5
10
15
20
25
LDI (
)
BaselineFollow-up visit
Monocular
30 days15 days7 days1 day
Binocular
(b)
05
1
15
2
25
3
Follow-up visit
MonocularBinocular
BFC I
rreg
ular
ity(m
m)
Baseline 30 days15 days7 days1 day
(c)
Figure 2 Monocular and binocular Best Fit Circle Radius (BFCr) (a) Light Distortion Index (LDI) (b) and BFC Irregularity (BFCIrregularity) parameter (c) of light distortion Bars represent the Standard Error of the Mean (SEM)
and CS were stable in the eyes that underwent overnight OK[7]
CS is a fundamental feature of vision and its measure-ment provides useful information about visual function thatmay not be obtained by standard visual acuity testing [13]CS has been subject of research in other fields such asrefractive surgery showing a significant decrease soon afterthe procedure [14 15] In the short term after both OK andcorneal refractive surgery corneal higher order aberrationsincrease and CSF decreases as the first response to treatmentIn the long term it has been reported that in the case ofrefractive surgery it recovers between 3 and 12 months aftertreatment reaching values similar to baseline [16 17] Similarresults have been found after OK treatment in the presentstudy with faster recoveryThis might be related with the fact
that in OK treatment no healing processes are involved andCS is recovered once the treatment is stabilized A potentiallimitation of our study is that we are considering cornealaberrations instead of total aberrationsThis might justify theweak correlations between visual function as measured withCSF or light distortion and aberrations
The impact of OK on visual performance however hasnot been studied in detailThere are few long-termOKstudiesin which the variation of higher order aberrations and CSFare studied [11] and one short-term study [10] in which lightdistortion is measured to investigate the correlation betweenpre- and posttreatment parameters and glare scores in OKsubjects who had used OK lenses for more than 3 months
In the present longitudinal study we investigated changesin perception of light distortion changes in corneal higher
Figure 3 Optical quality of the corneal front surface for different pupil sizes represented by the root mean square (RMS) of spherical-likeaberrations (a) coma-like aberrations (b) and secondary astigmatism (c) Bars represent the Standard Error of the Mean (SEM)
order aberrations and CSF as representative of visual qualityin eyes undergoing overnight OK for one year
The analysis of light distortion surrounding a light sourcehas proved to be effective in determining the time-courseof changes in visual quality from the subjectrsquos perspectiveand irrespective of the corneal higher order aberrationspattern observed A previous study by Villa et al used asimilar methodology but based on a software platform anda computer screen which is more limited in the presentationof bright stimuli In their study they reported an increasein light disturbances after corneal refractive surgery [18]Lorente-Velazquez et al used a different methodology toevaluate the effect of OK on the intraocular retinal stray lightover a period of 1 month using the C-Quant instrument
based on the compensation-comparison method to deriveretinal stray light [19] They observed that minor changes inthe stray light were not correlated with other psychophysicalparameters as the CSF Furthermore the authors reported animprovement in retinal stray light after 1 month comparedto baseline This suggests that stray light does not reflectthe impact of aberrations or any optical defects other thanchanges in the transparency of tissues Similarly Cervinoet al were not able to find any significant effect of LASIKsurgery on stray light values obtained with the C-Quant [20]while the analysis of halo size with a software system showedsignificant changes as others had previously found [18]Again this supports the assumption that the light distortionreported here is not related to stray light phenomena
Figure 4 Monocular (a) and binocular (b) log contrast sensitivity (CS) Bars represent the Standard Error of the Mean (SEM) only for visitson days 1 and 30 the remaining error bars are omitted for clarity
We observed an inverse correlation between coma-likeaberrations and CSF for medium and higher spatial fre-quencies which might be related to the relatively frequentdecentration and irregularity of the treatment zone after thefirst night wearing CL Our results showed no significant cor-relation between the different optical (corneal aberrations)and quality of vision (CSF and light distortion) parameters atthe end of the month The absence of significant correlationsat this stage might be interpreted as a neural adaptationprocess that is independent of the optical quality of thecornea A hypothetical component of this neural adaptationmight even take place at the retinal level with a change inthe apodization mechanism of the photoreceptors such thatthey overcome the effects of deteriorated peripheral opticsof the eye and take advantage of the relatively unchangedoptical quality within the more central part of the pupil Infact our results agree with previous reports by our group[5] that showed that the increase in corneal aberrations ishardly significant for a pupil size of 3mm or less whatmight explain visual quality remaining within normal limitsin the midterm despite the initial deterioration In anotherstudy analyzing subjective responses versus light distortionperception (whether it increases decreases or remains thesame) we found that after 1 year of treatment 421 reported adecrease and the remaining 579 reported that the subjectivefeeling of light distortion remained the same [8] In thepresent study light distortion analysis showed a transientincrease followed by a reduction to baseline levels after 7days of treatment This is in agreement with the clinicalobservation of adaptation to the distortion effect observedin our previous study [8] Similarly McAlinden et al usingthe Quality of Vision Questionnaire (QoV) [21] reported
a transient worsening of the subjective perception of qualityof vision that returned to baseline a few weeks after laser-assisted subepithelial keratectomy [22] Again the resultsof the QoV questionnaires after surgery showed a slowerrecovery which might be related with the healing processesoccurring in the cornea which are not present in the OKtreatment
Interestingly we observed a decrease in the distortionparameters related to the irregularity of the light distortionThis might be explained by the spherical aberration inducedthat leads to a more uniform and more radially symmetricdistortion pattern compared to baseline which will resultin a reduction of the irregularities in the form of spikessurrounding the light source Regarding aberration changesin the anterior corneal surface an average increase of 110for 30mm pupil to 233 for 60mm pupil in the spherical-like RMS was observed Changes in comatic aberration wereless severe and more similar for different pupil sizes rangingfrom 108 to 150 for 30 and 60mm pupil sizes Secondaryastigmatism showed a marked increase ranging from 62 to195 for 30 and 60mm pupil sizes Similar values have beenreported by other studies [5 6 23]
To our knowledge this is the first study addressing theshort-term changes in the optical quality of the anteriorcorneal surface and the visual quality determined by meansof monocular and binocular CSF and light distortion mea-surement Although the light distortion andCSF recovered tobaseline values the lack of correlation after 15 days betweenlight distortion andCSFmight confirm that bothmethods aremeasuring different aspects of visual quality
In summary we have shown that despite the reductionin optical quality of the anterior corneal surface some of the
BioMed Research International 7
parameters related to visual quality of the eye return to beingwithin normal range values within a narrow period of timeand this might be related with a neural adaptation process
Conflict of Interests
The authors have no proprietary interest in any of theinstruments or materials mentioned in this paper
Acknowledgments
This research was supported in part by Projects PTDCSAU-BEB0983912008FCOMP-01-0124-FEDER-010897 andPTDCSAU-BEB0983922008FCOMP-01-0124-FEDER-010898 The present work was presented in part at theCIOCV2012 conference (Braga April 9-10 2011)
References
[1] F Lu T Simpson L Sorbara and D Fonn ldquoCorneal refractivetherapy with different lens materials part 2 effect of oxygentransmissibility on corneal shape and optical characteristicsrdquoOptometry amp Vision Science vol 84 pp 349ndash356 2007
[2] A Queiros J M Gonzalez-Meijome C Villa-Collar A RGutierrez and J Jorge ldquoLocal steepening in peripheral cornealcurvature after corneal refractive therapy and LASIKrdquo Optom-etry and Vision Science vol 87 no 6 pp 432ndash439 2010
[3] S Haque D Fonn T Simpson and L Jones ldquoCorneal andepithelial thickness changes after 4 weeks of overnight cornealrefractive therapy lens wear measured with optical coherencetomographyrdquo Eye and Contact Lens vol 30 no 4 pp 189ndash1932004
[4] S Haque D Fonn T Simpson and L Jones ldquoCorneal refractivetherapy with different lens materials Part 1 corneal stromaland epithelial thickness changesrdquoOptometry andVision Sciencevol 84 no 4 pp 343ndash348 2007
[5] T Hiraoka Y Matsumoto F Okamoto et al ldquoCorneal higher-order aberrations induced by overnight orthokeratologyrdquoAmerican Journal of Ophthalmology vol 139 no 3 pp 429ndash4362005
[6] A Queiros C Villa-Collar J M Gonzalez-Meijome J Jorgeand A R Gutierrez ldquoEffect of pupil size on corneal aberrationsbefore and after standard laser in situ keratomileusis customlaser in situ keratomileusis and corneal refractive therapyrdquoTheAmerican Journal of Ophthalmology vol 150 no 1 pp 97e1ndash109e1 2010
[7] F Lu T Simpson L Sorbara and D Fonn ldquoThe relationshipbetween the treatment zone diameter and visual optical andsubjective performance in Corneal Refractive Therapy lenswearersrdquoOphthalmic and Physiological Optics vol 27 no 6 pp568ndash578 2007
[8] E Santolaria A Cervino A Queiros R Brautaset and JM Gonzalez-Meijome ldquoSubjective satisfaction in long-termorthokeratology patientsrdquo Eye and Contact Lens vol 39 no 6pp 388ndash393 2013
[9] A Queiros C Villa-Collar A R Gutierrez J Jorge and JM Gonzalez-Meijome ldquoQuality of life of myopic subjects withdifferent methods of visual correction using the NEI RQL-42questionnairerdquo Eye and Contact Lens vol 38 no 2 pp 116ndash1212012
[10] T Kojima A Hasegawa S Hara et al ldquoQuantitative evaluationof night vision and correlation of refractive and topographicalparameters with glare after orthokeratologyrdquoGraefersquos Archive forClinical and Experimental Ophthalmology vol 249 no 10 pp1519ndash1526 2011
[11] T Hiraoka C Okamoto Y Ishii T Kakita F Okamoto and TOshika ldquoTime course of changes in ocular higher-order aber-rations and contrast sensitivity after overnight orthokeratologyrdquoInvestigative Ophthalmology and Visual Science vol 49 no 10pp 4314ndash4320 2008
[12] J M M Linhares H Neves D Lopes-Ferreira M Faria-Ribeiro S C Peixoto-de-Matos and J M Gonzalez-MeijomeldquoRadiometric characterization of a novel LED array system forvisual assessmentrdquo Journal of Modern Optics vol 60 no 14 pp1136ndash1144 2013
[13] K Pesudovs C A Hazel R M L Doran and D B ElliottldquoThe usefulness of Vistech and FACT contrast sensitivity chartsfor cataract and refractive surgery outcomes researchrdquo BritishJournal of Ophthalmology vol 88 no 1 pp 11ndash16 2004
[14] J T Holladay D R Dudeja and J Chang ldquoFunctionalvision and corneal changes after laser in situ keratomileusisdetermined by contrast sensitivity glare testing and cornealtopographyrdquo Journal of Cataract and Refractive Surgery vol 25no 5 pp 663ndash669 1999
[15] N Yamane K Miyata T Samejima et al ldquoOcular higher-order aberrations and contrast sensitivity after conventionallaser in situ keratomileusisrdquo Investigative Ophthalmology andVisual Science vol 45 no 11 pp 3986ndash3990 2004
[16] S Mutyala M B McDonald K A Scheinblum M D OstrickS F Brint and H Thompson ldquoContrast sensitivity evaluationafter laser in situ keratomileusisrdquo Ophthalmology vol 107 no10 pp 1864ndash1867 2000
[17] J W W Chan M H Edwards G C Woo and V C P WooldquoContrast sensitivity after laser in situ keratomileusis one-yearfollow-uprdquo Journal of Cataract and Refractive Surgery vol 28no 10 pp 1774ndash1779 2002
[18] C Villa R Gutierrez J R Jimenez and J M Gonzalez-Meijome ldquoNight vision disturbances after successful LASIKsurgeryrdquo British Journal of Ophthalmology vol 91 no 8 pp1031ndash1037 2007
[19] A Lorente-Velazquez A Nieto-Bona C V Collar and A GMesa ldquoStraylight and contrast sensitivity after corneal refractivetherapyrdquoOptometry and Vision Science vol 88 no 10 pp 1245ndash1251 2011
[20] A Cervino C Villa-Collar J M Gonzalez-Meijome T Ferrer-Blasco and S Garcıa-Lazaro ldquoRetinal straylight and lightdistortion phenomena in normal and post-LASIK eyesrdquoGraefersquosArchive for Clinical and Experimental Ophthalmology vol 249no 10 pp 1561ndash1566 2011
[21] C McAlinden K Pesudovs and J E Moore ldquoThe developmentof an instrument to measure quality of vision the quality ofvision (QoV) questionnairerdquo Investigative Ophthalmology andVisual Science vol 51 no 11 pp 5537ndash5545 2010
[22] C McAlinden E Skiadaresi and J E Moore ldquoVisual andrefractive outcomes following myopic laser-assisted subepithe-lial keratectomy with a flying-spot excimer laserrdquo Journal ofCataract and Refractive Surgery vol 37 no 5 pp 901ndash906 2011
[23] THiraoka COkamoto Y Ishii T Kakita andTOshika ldquoCon-trast sensitivity function and ocular higher-order aberrationsfollowing overnight orthokeratologyrdquo Investigative Ophthalmol-ogy and Visual Science vol 48 no 2 pp 550ndash556 2007
Figure 2 Monocular and binocular Best Fit Circle Radius (BFCr) (a) Light Distortion Index (LDI) (b) and BFC Irregularity (BFCIrregularity) parameter (c) of light distortion Bars represent the Standard Error of the Mean (SEM)
and CS were stable in the eyes that underwent overnight OK[7]
CS is a fundamental feature of vision and its measure-ment provides useful information about visual function thatmay not be obtained by standard visual acuity testing [13]CS has been subject of research in other fields such asrefractive surgery showing a significant decrease soon afterthe procedure [14 15] In the short term after both OK andcorneal refractive surgery corneal higher order aberrationsincrease and CSF decreases as the first response to treatmentIn the long term it has been reported that in the case ofrefractive surgery it recovers between 3 and 12 months aftertreatment reaching values similar to baseline [16 17] Similarresults have been found after OK treatment in the presentstudy with faster recoveryThis might be related with the fact
that in OK treatment no healing processes are involved andCS is recovered once the treatment is stabilized A potentiallimitation of our study is that we are considering cornealaberrations instead of total aberrationsThis might justify theweak correlations between visual function as measured withCSF or light distortion and aberrations
The impact of OK on visual performance however hasnot been studied in detailThere are few long-termOKstudiesin which the variation of higher order aberrations and CSFare studied [11] and one short-term study [10] in which lightdistortion is measured to investigate the correlation betweenpre- and posttreatment parameters and glare scores in OKsubjects who had used OK lenses for more than 3 months
In the present longitudinal study we investigated changesin perception of light distortion changes in corneal higher
Figure 3 Optical quality of the corneal front surface for different pupil sizes represented by the root mean square (RMS) of spherical-likeaberrations (a) coma-like aberrations (b) and secondary astigmatism (c) Bars represent the Standard Error of the Mean (SEM)
order aberrations and CSF as representative of visual qualityin eyes undergoing overnight OK for one year
The analysis of light distortion surrounding a light sourcehas proved to be effective in determining the time-courseof changes in visual quality from the subjectrsquos perspectiveand irrespective of the corneal higher order aberrationspattern observed A previous study by Villa et al used asimilar methodology but based on a software platform anda computer screen which is more limited in the presentationof bright stimuli In their study they reported an increasein light disturbances after corneal refractive surgery [18]Lorente-Velazquez et al used a different methodology toevaluate the effect of OK on the intraocular retinal stray lightover a period of 1 month using the C-Quant instrument
based on the compensation-comparison method to deriveretinal stray light [19] They observed that minor changes inthe stray light were not correlated with other psychophysicalparameters as the CSF Furthermore the authors reported animprovement in retinal stray light after 1 month comparedto baseline This suggests that stray light does not reflectthe impact of aberrations or any optical defects other thanchanges in the transparency of tissues Similarly Cervinoet al were not able to find any significant effect of LASIKsurgery on stray light values obtained with the C-Quant [20]while the analysis of halo size with a software system showedsignificant changes as others had previously found [18]Again this supports the assumption that the light distortionreported here is not related to stray light phenomena
Figure 4 Monocular (a) and binocular (b) log contrast sensitivity (CS) Bars represent the Standard Error of the Mean (SEM) only for visitson days 1 and 30 the remaining error bars are omitted for clarity
We observed an inverse correlation between coma-likeaberrations and CSF for medium and higher spatial fre-quencies which might be related to the relatively frequentdecentration and irregularity of the treatment zone after thefirst night wearing CL Our results showed no significant cor-relation between the different optical (corneal aberrations)and quality of vision (CSF and light distortion) parameters atthe end of the month The absence of significant correlationsat this stage might be interpreted as a neural adaptationprocess that is independent of the optical quality of thecornea A hypothetical component of this neural adaptationmight even take place at the retinal level with a change inthe apodization mechanism of the photoreceptors such thatthey overcome the effects of deteriorated peripheral opticsof the eye and take advantage of the relatively unchangedoptical quality within the more central part of the pupil Infact our results agree with previous reports by our group[5] that showed that the increase in corneal aberrations ishardly significant for a pupil size of 3mm or less whatmight explain visual quality remaining within normal limitsin the midterm despite the initial deterioration In anotherstudy analyzing subjective responses versus light distortionperception (whether it increases decreases or remains thesame) we found that after 1 year of treatment 421 reported adecrease and the remaining 579 reported that the subjectivefeeling of light distortion remained the same [8] In thepresent study light distortion analysis showed a transientincrease followed by a reduction to baseline levels after 7days of treatment This is in agreement with the clinicalobservation of adaptation to the distortion effect observedin our previous study [8] Similarly McAlinden et al usingthe Quality of Vision Questionnaire (QoV) [21] reported
a transient worsening of the subjective perception of qualityof vision that returned to baseline a few weeks after laser-assisted subepithelial keratectomy [22] Again the resultsof the QoV questionnaires after surgery showed a slowerrecovery which might be related with the healing processesoccurring in the cornea which are not present in the OKtreatment
Interestingly we observed a decrease in the distortionparameters related to the irregularity of the light distortionThis might be explained by the spherical aberration inducedthat leads to a more uniform and more radially symmetricdistortion pattern compared to baseline which will resultin a reduction of the irregularities in the form of spikessurrounding the light source Regarding aberration changesin the anterior corneal surface an average increase of 110for 30mm pupil to 233 for 60mm pupil in the spherical-like RMS was observed Changes in comatic aberration wereless severe and more similar for different pupil sizes rangingfrom 108 to 150 for 30 and 60mm pupil sizes Secondaryastigmatism showed a marked increase ranging from 62 to195 for 30 and 60mm pupil sizes Similar values have beenreported by other studies [5 6 23]
To our knowledge this is the first study addressing theshort-term changes in the optical quality of the anteriorcorneal surface and the visual quality determined by meansof monocular and binocular CSF and light distortion mea-surement Although the light distortion andCSF recovered tobaseline values the lack of correlation after 15 days betweenlight distortion andCSFmight confirm that bothmethods aremeasuring different aspects of visual quality
In summary we have shown that despite the reductionin optical quality of the anterior corneal surface some of the
BioMed Research International 7
parameters related to visual quality of the eye return to beingwithin normal range values within a narrow period of timeand this might be related with a neural adaptation process
Conflict of Interests
The authors have no proprietary interest in any of theinstruments or materials mentioned in this paper
Acknowledgments
This research was supported in part by Projects PTDCSAU-BEB0983912008FCOMP-01-0124-FEDER-010897 andPTDCSAU-BEB0983922008FCOMP-01-0124-FEDER-010898 The present work was presented in part at theCIOCV2012 conference (Braga April 9-10 2011)
References
[1] F Lu T Simpson L Sorbara and D Fonn ldquoCorneal refractivetherapy with different lens materials part 2 effect of oxygentransmissibility on corneal shape and optical characteristicsrdquoOptometry amp Vision Science vol 84 pp 349ndash356 2007
[2] A Queiros J M Gonzalez-Meijome C Villa-Collar A RGutierrez and J Jorge ldquoLocal steepening in peripheral cornealcurvature after corneal refractive therapy and LASIKrdquo Optom-etry and Vision Science vol 87 no 6 pp 432ndash439 2010
[3] S Haque D Fonn T Simpson and L Jones ldquoCorneal andepithelial thickness changes after 4 weeks of overnight cornealrefractive therapy lens wear measured with optical coherencetomographyrdquo Eye and Contact Lens vol 30 no 4 pp 189ndash1932004
[4] S Haque D Fonn T Simpson and L Jones ldquoCorneal refractivetherapy with different lens materials Part 1 corneal stromaland epithelial thickness changesrdquoOptometry andVision Sciencevol 84 no 4 pp 343ndash348 2007
[5] T Hiraoka Y Matsumoto F Okamoto et al ldquoCorneal higher-order aberrations induced by overnight orthokeratologyrdquoAmerican Journal of Ophthalmology vol 139 no 3 pp 429ndash4362005
[6] A Queiros C Villa-Collar J M Gonzalez-Meijome J Jorgeand A R Gutierrez ldquoEffect of pupil size on corneal aberrationsbefore and after standard laser in situ keratomileusis customlaser in situ keratomileusis and corneal refractive therapyrdquoTheAmerican Journal of Ophthalmology vol 150 no 1 pp 97e1ndash109e1 2010
[7] F Lu T Simpson L Sorbara and D Fonn ldquoThe relationshipbetween the treatment zone diameter and visual optical andsubjective performance in Corneal Refractive Therapy lenswearersrdquoOphthalmic and Physiological Optics vol 27 no 6 pp568ndash578 2007
[8] E Santolaria A Cervino A Queiros R Brautaset and JM Gonzalez-Meijome ldquoSubjective satisfaction in long-termorthokeratology patientsrdquo Eye and Contact Lens vol 39 no 6pp 388ndash393 2013
[9] A Queiros C Villa-Collar A R Gutierrez J Jorge and JM Gonzalez-Meijome ldquoQuality of life of myopic subjects withdifferent methods of visual correction using the NEI RQL-42questionnairerdquo Eye and Contact Lens vol 38 no 2 pp 116ndash1212012
[10] T Kojima A Hasegawa S Hara et al ldquoQuantitative evaluationof night vision and correlation of refractive and topographicalparameters with glare after orthokeratologyrdquoGraefersquos Archive forClinical and Experimental Ophthalmology vol 249 no 10 pp1519ndash1526 2011
[11] T Hiraoka C Okamoto Y Ishii T Kakita F Okamoto and TOshika ldquoTime course of changes in ocular higher-order aber-rations and contrast sensitivity after overnight orthokeratologyrdquoInvestigative Ophthalmology and Visual Science vol 49 no 10pp 4314ndash4320 2008
[12] J M M Linhares H Neves D Lopes-Ferreira M Faria-Ribeiro S C Peixoto-de-Matos and J M Gonzalez-MeijomeldquoRadiometric characterization of a novel LED array system forvisual assessmentrdquo Journal of Modern Optics vol 60 no 14 pp1136ndash1144 2013
[13] K Pesudovs C A Hazel R M L Doran and D B ElliottldquoThe usefulness of Vistech and FACT contrast sensitivity chartsfor cataract and refractive surgery outcomes researchrdquo BritishJournal of Ophthalmology vol 88 no 1 pp 11ndash16 2004
[14] J T Holladay D R Dudeja and J Chang ldquoFunctionalvision and corneal changes after laser in situ keratomileusisdetermined by contrast sensitivity glare testing and cornealtopographyrdquo Journal of Cataract and Refractive Surgery vol 25no 5 pp 663ndash669 1999
[15] N Yamane K Miyata T Samejima et al ldquoOcular higher-order aberrations and contrast sensitivity after conventionallaser in situ keratomileusisrdquo Investigative Ophthalmology andVisual Science vol 45 no 11 pp 3986ndash3990 2004
[16] S Mutyala M B McDonald K A Scheinblum M D OstrickS F Brint and H Thompson ldquoContrast sensitivity evaluationafter laser in situ keratomileusisrdquo Ophthalmology vol 107 no10 pp 1864ndash1867 2000
[17] J W W Chan M H Edwards G C Woo and V C P WooldquoContrast sensitivity after laser in situ keratomileusis one-yearfollow-uprdquo Journal of Cataract and Refractive Surgery vol 28no 10 pp 1774ndash1779 2002
[18] C Villa R Gutierrez J R Jimenez and J M Gonzalez-Meijome ldquoNight vision disturbances after successful LASIKsurgeryrdquo British Journal of Ophthalmology vol 91 no 8 pp1031ndash1037 2007
[19] A Lorente-Velazquez A Nieto-Bona C V Collar and A GMesa ldquoStraylight and contrast sensitivity after corneal refractivetherapyrdquoOptometry and Vision Science vol 88 no 10 pp 1245ndash1251 2011
[20] A Cervino C Villa-Collar J M Gonzalez-Meijome T Ferrer-Blasco and S Garcıa-Lazaro ldquoRetinal straylight and lightdistortion phenomena in normal and post-LASIK eyesrdquoGraefersquosArchive for Clinical and Experimental Ophthalmology vol 249no 10 pp 1561ndash1566 2011
[21] C McAlinden K Pesudovs and J E Moore ldquoThe developmentof an instrument to measure quality of vision the quality ofvision (QoV) questionnairerdquo Investigative Ophthalmology andVisual Science vol 51 no 11 pp 5537ndash5545 2010
[22] C McAlinden E Skiadaresi and J E Moore ldquoVisual andrefractive outcomes following myopic laser-assisted subepithe-lial keratectomy with a flying-spot excimer laserrdquo Journal ofCataract and Refractive Surgery vol 37 no 5 pp 901ndash906 2011
[23] THiraoka COkamoto Y Ishii T Kakita andTOshika ldquoCon-trast sensitivity function and ocular higher-order aberrationsfollowing overnight orthokeratologyrdquo Investigative Ophthalmol-ogy and Visual Science vol 48 no 2 pp 550ndash556 2007
Figure 3 Optical quality of the corneal front surface for different pupil sizes represented by the root mean square (RMS) of spherical-likeaberrations (a) coma-like aberrations (b) and secondary astigmatism (c) Bars represent the Standard Error of the Mean (SEM)
order aberrations and CSF as representative of visual qualityin eyes undergoing overnight OK for one year
The analysis of light distortion surrounding a light sourcehas proved to be effective in determining the time-courseof changes in visual quality from the subjectrsquos perspectiveand irrespective of the corneal higher order aberrationspattern observed A previous study by Villa et al used asimilar methodology but based on a software platform anda computer screen which is more limited in the presentationof bright stimuli In their study they reported an increasein light disturbances after corneal refractive surgery [18]Lorente-Velazquez et al used a different methodology toevaluate the effect of OK on the intraocular retinal stray lightover a period of 1 month using the C-Quant instrument
based on the compensation-comparison method to deriveretinal stray light [19] They observed that minor changes inthe stray light were not correlated with other psychophysicalparameters as the CSF Furthermore the authors reported animprovement in retinal stray light after 1 month comparedto baseline This suggests that stray light does not reflectthe impact of aberrations or any optical defects other thanchanges in the transparency of tissues Similarly Cervinoet al were not able to find any significant effect of LASIKsurgery on stray light values obtained with the C-Quant [20]while the analysis of halo size with a software system showedsignificant changes as others had previously found [18]Again this supports the assumption that the light distortionreported here is not related to stray light phenomena
Figure 4 Monocular (a) and binocular (b) log contrast sensitivity (CS) Bars represent the Standard Error of the Mean (SEM) only for visitson days 1 and 30 the remaining error bars are omitted for clarity
We observed an inverse correlation between coma-likeaberrations and CSF for medium and higher spatial fre-quencies which might be related to the relatively frequentdecentration and irregularity of the treatment zone after thefirst night wearing CL Our results showed no significant cor-relation between the different optical (corneal aberrations)and quality of vision (CSF and light distortion) parameters atthe end of the month The absence of significant correlationsat this stage might be interpreted as a neural adaptationprocess that is independent of the optical quality of thecornea A hypothetical component of this neural adaptationmight even take place at the retinal level with a change inthe apodization mechanism of the photoreceptors such thatthey overcome the effects of deteriorated peripheral opticsof the eye and take advantage of the relatively unchangedoptical quality within the more central part of the pupil Infact our results agree with previous reports by our group[5] that showed that the increase in corneal aberrations ishardly significant for a pupil size of 3mm or less whatmight explain visual quality remaining within normal limitsin the midterm despite the initial deterioration In anotherstudy analyzing subjective responses versus light distortionperception (whether it increases decreases or remains thesame) we found that after 1 year of treatment 421 reported adecrease and the remaining 579 reported that the subjectivefeeling of light distortion remained the same [8] In thepresent study light distortion analysis showed a transientincrease followed by a reduction to baseline levels after 7days of treatment This is in agreement with the clinicalobservation of adaptation to the distortion effect observedin our previous study [8] Similarly McAlinden et al usingthe Quality of Vision Questionnaire (QoV) [21] reported
a transient worsening of the subjective perception of qualityof vision that returned to baseline a few weeks after laser-assisted subepithelial keratectomy [22] Again the resultsof the QoV questionnaires after surgery showed a slowerrecovery which might be related with the healing processesoccurring in the cornea which are not present in the OKtreatment
Interestingly we observed a decrease in the distortionparameters related to the irregularity of the light distortionThis might be explained by the spherical aberration inducedthat leads to a more uniform and more radially symmetricdistortion pattern compared to baseline which will resultin a reduction of the irregularities in the form of spikessurrounding the light source Regarding aberration changesin the anterior corneal surface an average increase of 110for 30mm pupil to 233 for 60mm pupil in the spherical-like RMS was observed Changes in comatic aberration wereless severe and more similar for different pupil sizes rangingfrom 108 to 150 for 30 and 60mm pupil sizes Secondaryastigmatism showed a marked increase ranging from 62 to195 for 30 and 60mm pupil sizes Similar values have beenreported by other studies [5 6 23]
To our knowledge this is the first study addressing theshort-term changes in the optical quality of the anteriorcorneal surface and the visual quality determined by meansof monocular and binocular CSF and light distortion mea-surement Although the light distortion andCSF recovered tobaseline values the lack of correlation after 15 days betweenlight distortion andCSFmight confirm that bothmethods aremeasuring different aspects of visual quality
In summary we have shown that despite the reductionin optical quality of the anterior corneal surface some of the
BioMed Research International 7
parameters related to visual quality of the eye return to beingwithin normal range values within a narrow period of timeand this might be related with a neural adaptation process
Conflict of Interests
The authors have no proprietary interest in any of theinstruments or materials mentioned in this paper
Acknowledgments
This research was supported in part by Projects PTDCSAU-BEB0983912008FCOMP-01-0124-FEDER-010897 andPTDCSAU-BEB0983922008FCOMP-01-0124-FEDER-010898 The present work was presented in part at theCIOCV2012 conference (Braga April 9-10 2011)
References
[1] F Lu T Simpson L Sorbara and D Fonn ldquoCorneal refractivetherapy with different lens materials part 2 effect of oxygentransmissibility on corneal shape and optical characteristicsrdquoOptometry amp Vision Science vol 84 pp 349ndash356 2007
[2] A Queiros J M Gonzalez-Meijome C Villa-Collar A RGutierrez and J Jorge ldquoLocal steepening in peripheral cornealcurvature after corneal refractive therapy and LASIKrdquo Optom-etry and Vision Science vol 87 no 6 pp 432ndash439 2010
[3] S Haque D Fonn T Simpson and L Jones ldquoCorneal andepithelial thickness changes after 4 weeks of overnight cornealrefractive therapy lens wear measured with optical coherencetomographyrdquo Eye and Contact Lens vol 30 no 4 pp 189ndash1932004
[4] S Haque D Fonn T Simpson and L Jones ldquoCorneal refractivetherapy with different lens materials Part 1 corneal stromaland epithelial thickness changesrdquoOptometry andVision Sciencevol 84 no 4 pp 343ndash348 2007
[5] T Hiraoka Y Matsumoto F Okamoto et al ldquoCorneal higher-order aberrations induced by overnight orthokeratologyrdquoAmerican Journal of Ophthalmology vol 139 no 3 pp 429ndash4362005
[6] A Queiros C Villa-Collar J M Gonzalez-Meijome J Jorgeand A R Gutierrez ldquoEffect of pupil size on corneal aberrationsbefore and after standard laser in situ keratomileusis customlaser in situ keratomileusis and corneal refractive therapyrdquoTheAmerican Journal of Ophthalmology vol 150 no 1 pp 97e1ndash109e1 2010
[7] F Lu T Simpson L Sorbara and D Fonn ldquoThe relationshipbetween the treatment zone diameter and visual optical andsubjective performance in Corneal Refractive Therapy lenswearersrdquoOphthalmic and Physiological Optics vol 27 no 6 pp568ndash578 2007
[8] E Santolaria A Cervino A Queiros R Brautaset and JM Gonzalez-Meijome ldquoSubjective satisfaction in long-termorthokeratology patientsrdquo Eye and Contact Lens vol 39 no 6pp 388ndash393 2013
[9] A Queiros C Villa-Collar A R Gutierrez J Jorge and JM Gonzalez-Meijome ldquoQuality of life of myopic subjects withdifferent methods of visual correction using the NEI RQL-42questionnairerdquo Eye and Contact Lens vol 38 no 2 pp 116ndash1212012
[10] T Kojima A Hasegawa S Hara et al ldquoQuantitative evaluationof night vision and correlation of refractive and topographicalparameters with glare after orthokeratologyrdquoGraefersquos Archive forClinical and Experimental Ophthalmology vol 249 no 10 pp1519ndash1526 2011
[11] T Hiraoka C Okamoto Y Ishii T Kakita F Okamoto and TOshika ldquoTime course of changes in ocular higher-order aber-rations and contrast sensitivity after overnight orthokeratologyrdquoInvestigative Ophthalmology and Visual Science vol 49 no 10pp 4314ndash4320 2008
[12] J M M Linhares H Neves D Lopes-Ferreira M Faria-Ribeiro S C Peixoto-de-Matos and J M Gonzalez-MeijomeldquoRadiometric characterization of a novel LED array system forvisual assessmentrdquo Journal of Modern Optics vol 60 no 14 pp1136ndash1144 2013
[13] K Pesudovs C A Hazel R M L Doran and D B ElliottldquoThe usefulness of Vistech and FACT contrast sensitivity chartsfor cataract and refractive surgery outcomes researchrdquo BritishJournal of Ophthalmology vol 88 no 1 pp 11ndash16 2004
[14] J T Holladay D R Dudeja and J Chang ldquoFunctionalvision and corneal changes after laser in situ keratomileusisdetermined by contrast sensitivity glare testing and cornealtopographyrdquo Journal of Cataract and Refractive Surgery vol 25no 5 pp 663ndash669 1999
[15] N Yamane K Miyata T Samejima et al ldquoOcular higher-order aberrations and contrast sensitivity after conventionallaser in situ keratomileusisrdquo Investigative Ophthalmology andVisual Science vol 45 no 11 pp 3986ndash3990 2004
[16] S Mutyala M B McDonald K A Scheinblum M D OstrickS F Brint and H Thompson ldquoContrast sensitivity evaluationafter laser in situ keratomileusisrdquo Ophthalmology vol 107 no10 pp 1864ndash1867 2000
[17] J W W Chan M H Edwards G C Woo and V C P WooldquoContrast sensitivity after laser in situ keratomileusis one-yearfollow-uprdquo Journal of Cataract and Refractive Surgery vol 28no 10 pp 1774ndash1779 2002
[18] C Villa R Gutierrez J R Jimenez and J M Gonzalez-Meijome ldquoNight vision disturbances after successful LASIKsurgeryrdquo British Journal of Ophthalmology vol 91 no 8 pp1031ndash1037 2007
[19] A Lorente-Velazquez A Nieto-Bona C V Collar and A GMesa ldquoStraylight and contrast sensitivity after corneal refractivetherapyrdquoOptometry and Vision Science vol 88 no 10 pp 1245ndash1251 2011
[20] A Cervino C Villa-Collar J M Gonzalez-Meijome T Ferrer-Blasco and S Garcıa-Lazaro ldquoRetinal straylight and lightdistortion phenomena in normal and post-LASIK eyesrdquoGraefersquosArchive for Clinical and Experimental Ophthalmology vol 249no 10 pp 1561ndash1566 2011
[21] C McAlinden K Pesudovs and J E Moore ldquoThe developmentof an instrument to measure quality of vision the quality ofvision (QoV) questionnairerdquo Investigative Ophthalmology andVisual Science vol 51 no 11 pp 5537ndash5545 2010
[22] C McAlinden E Skiadaresi and J E Moore ldquoVisual andrefractive outcomes following myopic laser-assisted subepithe-lial keratectomy with a flying-spot excimer laserrdquo Journal ofCataract and Refractive Surgery vol 37 no 5 pp 901ndash906 2011
[23] THiraoka COkamoto Y Ishii T Kakita andTOshika ldquoCon-trast sensitivity function and ocular higher-order aberrationsfollowing overnight orthokeratologyrdquo Investigative Ophthalmol-ogy and Visual Science vol 48 no 2 pp 550ndash556 2007
Figure 4 Monocular (a) and binocular (b) log contrast sensitivity (CS) Bars represent the Standard Error of the Mean (SEM) only for visitson days 1 and 30 the remaining error bars are omitted for clarity
We observed an inverse correlation between coma-likeaberrations and CSF for medium and higher spatial fre-quencies which might be related to the relatively frequentdecentration and irregularity of the treatment zone after thefirst night wearing CL Our results showed no significant cor-relation between the different optical (corneal aberrations)and quality of vision (CSF and light distortion) parameters atthe end of the month The absence of significant correlationsat this stage might be interpreted as a neural adaptationprocess that is independent of the optical quality of thecornea A hypothetical component of this neural adaptationmight even take place at the retinal level with a change inthe apodization mechanism of the photoreceptors such thatthey overcome the effects of deteriorated peripheral opticsof the eye and take advantage of the relatively unchangedoptical quality within the more central part of the pupil Infact our results agree with previous reports by our group[5] that showed that the increase in corneal aberrations ishardly significant for a pupil size of 3mm or less whatmight explain visual quality remaining within normal limitsin the midterm despite the initial deterioration In anotherstudy analyzing subjective responses versus light distortionperception (whether it increases decreases or remains thesame) we found that after 1 year of treatment 421 reported adecrease and the remaining 579 reported that the subjectivefeeling of light distortion remained the same [8] In thepresent study light distortion analysis showed a transientincrease followed by a reduction to baseline levels after 7days of treatment This is in agreement with the clinicalobservation of adaptation to the distortion effect observedin our previous study [8] Similarly McAlinden et al usingthe Quality of Vision Questionnaire (QoV) [21] reported
a transient worsening of the subjective perception of qualityof vision that returned to baseline a few weeks after laser-assisted subepithelial keratectomy [22] Again the resultsof the QoV questionnaires after surgery showed a slowerrecovery which might be related with the healing processesoccurring in the cornea which are not present in the OKtreatment
Interestingly we observed a decrease in the distortionparameters related to the irregularity of the light distortionThis might be explained by the spherical aberration inducedthat leads to a more uniform and more radially symmetricdistortion pattern compared to baseline which will resultin a reduction of the irregularities in the form of spikessurrounding the light source Regarding aberration changesin the anterior corneal surface an average increase of 110for 30mm pupil to 233 for 60mm pupil in the spherical-like RMS was observed Changes in comatic aberration wereless severe and more similar for different pupil sizes rangingfrom 108 to 150 for 30 and 60mm pupil sizes Secondaryastigmatism showed a marked increase ranging from 62 to195 for 30 and 60mm pupil sizes Similar values have beenreported by other studies [5 6 23]
To our knowledge this is the first study addressing theshort-term changes in the optical quality of the anteriorcorneal surface and the visual quality determined by meansof monocular and binocular CSF and light distortion mea-surement Although the light distortion andCSF recovered tobaseline values the lack of correlation after 15 days betweenlight distortion andCSFmight confirm that bothmethods aremeasuring different aspects of visual quality
In summary we have shown that despite the reductionin optical quality of the anterior corneal surface some of the
BioMed Research International 7
parameters related to visual quality of the eye return to beingwithin normal range values within a narrow period of timeand this might be related with a neural adaptation process
Conflict of Interests
The authors have no proprietary interest in any of theinstruments or materials mentioned in this paper
Acknowledgments
This research was supported in part by Projects PTDCSAU-BEB0983912008FCOMP-01-0124-FEDER-010897 andPTDCSAU-BEB0983922008FCOMP-01-0124-FEDER-010898 The present work was presented in part at theCIOCV2012 conference (Braga April 9-10 2011)
References
[1] F Lu T Simpson L Sorbara and D Fonn ldquoCorneal refractivetherapy with different lens materials part 2 effect of oxygentransmissibility on corneal shape and optical characteristicsrdquoOptometry amp Vision Science vol 84 pp 349ndash356 2007
[2] A Queiros J M Gonzalez-Meijome C Villa-Collar A RGutierrez and J Jorge ldquoLocal steepening in peripheral cornealcurvature after corneal refractive therapy and LASIKrdquo Optom-etry and Vision Science vol 87 no 6 pp 432ndash439 2010
[3] S Haque D Fonn T Simpson and L Jones ldquoCorneal andepithelial thickness changes after 4 weeks of overnight cornealrefractive therapy lens wear measured with optical coherencetomographyrdquo Eye and Contact Lens vol 30 no 4 pp 189ndash1932004
[4] S Haque D Fonn T Simpson and L Jones ldquoCorneal refractivetherapy with different lens materials Part 1 corneal stromaland epithelial thickness changesrdquoOptometry andVision Sciencevol 84 no 4 pp 343ndash348 2007
[5] T Hiraoka Y Matsumoto F Okamoto et al ldquoCorneal higher-order aberrations induced by overnight orthokeratologyrdquoAmerican Journal of Ophthalmology vol 139 no 3 pp 429ndash4362005
[6] A Queiros C Villa-Collar J M Gonzalez-Meijome J Jorgeand A R Gutierrez ldquoEffect of pupil size on corneal aberrationsbefore and after standard laser in situ keratomileusis customlaser in situ keratomileusis and corneal refractive therapyrdquoTheAmerican Journal of Ophthalmology vol 150 no 1 pp 97e1ndash109e1 2010
[7] F Lu T Simpson L Sorbara and D Fonn ldquoThe relationshipbetween the treatment zone diameter and visual optical andsubjective performance in Corneal Refractive Therapy lenswearersrdquoOphthalmic and Physiological Optics vol 27 no 6 pp568ndash578 2007
[8] E Santolaria A Cervino A Queiros R Brautaset and JM Gonzalez-Meijome ldquoSubjective satisfaction in long-termorthokeratology patientsrdquo Eye and Contact Lens vol 39 no 6pp 388ndash393 2013
[9] A Queiros C Villa-Collar A R Gutierrez J Jorge and JM Gonzalez-Meijome ldquoQuality of life of myopic subjects withdifferent methods of visual correction using the NEI RQL-42questionnairerdquo Eye and Contact Lens vol 38 no 2 pp 116ndash1212012
[10] T Kojima A Hasegawa S Hara et al ldquoQuantitative evaluationof night vision and correlation of refractive and topographicalparameters with glare after orthokeratologyrdquoGraefersquos Archive forClinical and Experimental Ophthalmology vol 249 no 10 pp1519ndash1526 2011
[11] T Hiraoka C Okamoto Y Ishii T Kakita F Okamoto and TOshika ldquoTime course of changes in ocular higher-order aber-rations and contrast sensitivity after overnight orthokeratologyrdquoInvestigative Ophthalmology and Visual Science vol 49 no 10pp 4314ndash4320 2008
[12] J M M Linhares H Neves D Lopes-Ferreira M Faria-Ribeiro S C Peixoto-de-Matos and J M Gonzalez-MeijomeldquoRadiometric characterization of a novel LED array system forvisual assessmentrdquo Journal of Modern Optics vol 60 no 14 pp1136ndash1144 2013
[13] K Pesudovs C A Hazel R M L Doran and D B ElliottldquoThe usefulness of Vistech and FACT contrast sensitivity chartsfor cataract and refractive surgery outcomes researchrdquo BritishJournal of Ophthalmology vol 88 no 1 pp 11ndash16 2004
[14] J T Holladay D R Dudeja and J Chang ldquoFunctionalvision and corneal changes after laser in situ keratomileusisdetermined by contrast sensitivity glare testing and cornealtopographyrdquo Journal of Cataract and Refractive Surgery vol 25no 5 pp 663ndash669 1999
[15] N Yamane K Miyata T Samejima et al ldquoOcular higher-order aberrations and contrast sensitivity after conventionallaser in situ keratomileusisrdquo Investigative Ophthalmology andVisual Science vol 45 no 11 pp 3986ndash3990 2004
[16] S Mutyala M B McDonald K A Scheinblum M D OstrickS F Brint and H Thompson ldquoContrast sensitivity evaluationafter laser in situ keratomileusisrdquo Ophthalmology vol 107 no10 pp 1864ndash1867 2000
[17] J W W Chan M H Edwards G C Woo and V C P WooldquoContrast sensitivity after laser in situ keratomileusis one-yearfollow-uprdquo Journal of Cataract and Refractive Surgery vol 28no 10 pp 1774ndash1779 2002
[18] C Villa R Gutierrez J R Jimenez and J M Gonzalez-Meijome ldquoNight vision disturbances after successful LASIKsurgeryrdquo British Journal of Ophthalmology vol 91 no 8 pp1031ndash1037 2007
[19] A Lorente-Velazquez A Nieto-Bona C V Collar and A GMesa ldquoStraylight and contrast sensitivity after corneal refractivetherapyrdquoOptometry and Vision Science vol 88 no 10 pp 1245ndash1251 2011
[20] A Cervino C Villa-Collar J M Gonzalez-Meijome T Ferrer-Blasco and S Garcıa-Lazaro ldquoRetinal straylight and lightdistortion phenomena in normal and post-LASIK eyesrdquoGraefersquosArchive for Clinical and Experimental Ophthalmology vol 249no 10 pp 1561ndash1566 2011
[21] C McAlinden K Pesudovs and J E Moore ldquoThe developmentof an instrument to measure quality of vision the quality ofvision (QoV) questionnairerdquo Investigative Ophthalmology andVisual Science vol 51 no 11 pp 5537ndash5545 2010
[22] C McAlinden E Skiadaresi and J E Moore ldquoVisual andrefractive outcomes following myopic laser-assisted subepithe-lial keratectomy with a flying-spot excimer laserrdquo Journal ofCataract and Refractive Surgery vol 37 no 5 pp 901ndash906 2011
[23] THiraoka COkamoto Y Ishii T Kakita andTOshika ldquoCon-trast sensitivity function and ocular higher-order aberrationsfollowing overnight orthokeratologyrdquo Investigative Ophthalmol-ogy and Visual Science vol 48 no 2 pp 550ndash556 2007
parameters related to visual quality of the eye return to beingwithin normal range values within a narrow period of timeand this might be related with a neural adaptation process
Conflict of Interests
The authors have no proprietary interest in any of theinstruments or materials mentioned in this paper
Acknowledgments
This research was supported in part by Projects PTDCSAU-BEB0983912008FCOMP-01-0124-FEDER-010897 andPTDCSAU-BEB0983922008FCOMP-01-0124-FEDER-010898 The present work was presented in part at theCIOCV2012 conference (Braga April 9-10 2011)
References
[1] F Lu T Simpson L Sorbara and D Fonn ldquoCorneal refractivetherapy with different lens materials part 2 effect of oxygentransmissibility on corneal shape and optical characteristicsrdquoOptometry amp Vision Science vol 84 pp 349ndash356 2007
[2] A Queiros J M Gonzalez-Meijome C Villa-Collar A RGutierrez and J Jorge ldquoLocal steepening in peripheral cornealcurvature after corneal refractive therapy and LASIKrdquo Optom-etry and Vision Science vol 87 no 6 pp 432ndash439 2010
[3] S Haque D Fonn T Simpson and L Jones ldquoCorneal andepithelial thickness changes after 4 weeks of overnight cornealrefractive therapy lens wear measured with optical coherencetomographyrdquo Eye and Contact Lens vol 30 no 4 pp 189ndash1932004
[4] S Haque D Fonn T Simpson and L Jones ldquoCorneal refractivetherapy with different lens materials Part 1 corneal stromaland epithelial thickness changesrdquoOptometry andVision Sciencevol 84 no 4 pp 343ndash348 2007
[5] T Hiraoka Y Matsumoto F Okamoto et al ldquoCorneal higher-order aberrations induced by overnight orthokeratologyrdquoAmerican Journal of Ophthalmology vol 139 no 3 pp 429ndash4362005
[6] A Queiros C Villa-Collar J M Gonzalez-Meijome J Jorgeand A R Gutierrez ldquoEffect of pupil size on corneal aberrationsbefore and after standard laser in situ keratomileusis customlaser in situ keratomileusis and corneal refractive therapyrdquoTheAmerican Journal of Ophthalmology vol 150 no 1 pp 97e1ndash109e1 2010
[7] F Lu T Simpson L Sorbara and D Fonn ldquoThe relationshipbetween the treatment zone diameter and visual optical andsubjective performance in Corneal Refractive Therapy lenswearersrdquoOphthalmic and Physiological Optics vol 27 no 6 pp568ndash578 2007
[8] E Santolaria A Cervino A Queiros R Brautaset and JM Gonzalez-Meijome ldquoSubjective satisfaction in long-termorthokeratology patientsrdquo Eye and Contact Lens vol 39 no 6pp 388ndash393 2013
[9] A Queiros C Villa-Collar A R Gutierrez J Jorge and JM Gonzalez-Meijome ldquoQuality of life of myopic subjects withdifferent methods of visual correction using the NEI RQL-42questionnairerdquo Eye and Contact Lens vol 38 no 2 pp 116ndash1212012
[10] T Kojima A Hasegawa S Hara et al ldquoQuantitative evaluationof night vision and correlation of refractive and topographicalparameters with glare after orthokeratologyrdquoGraefersquos Archive forClinical and Experimental Ophthalmology vol 249 no 10 pp1519ndash1526 2011
[11] T Hiraoka C Okamoto Y Ishii T Kakita F Okamoto and TOshika ldquoTime course of changes in ocular higher-order aber-rations and contrast sensitivity after overnight orthokeratologyrdquoInvestigative Ophthalmology and Visual Science vol 49 no 10pp 4314ndash4320 2008
[12] J M M Linhares H Neves D Lopes-Ferreira M Faria-Ribeiro S C Peixoto-de-Matos and J M Gonzalez-MeijomeldquoRadiometric characterization of a novel LED array system forvisual assessmentrdquo Journal of Modern Optics vol 60 no 14 pp1136ndash1144 2013
[13] K Pesudovs C A Hazel R M L Doran and D B ElliottldquoThe usefulness of Vistech and FACT contrast sensitivity chartsfor cataract and refractive surgery outcomes researchrdquo BritishJournal of Ophthalmology vol 88 no 1 pp 11ndash16 2004
[14] J T Holladay D R Dudeja and J Chang ldquoFunctionalvision and corneal changes after laser in situ keratomileusisdetermined by contrast sensitivity glare testing and cornealtopographyrdquo Journal of Cataract and Refractive Surgery vol 25no 5 pp 663ndash669 1999
[15] N Yamane K Miyata T Samejima et al ldquoOcular higher-order aberrations and contrast sensitivity after conventionallaser in situ keratomileusisrdquo Investigative Ophthalmology andVisual Science vol 45 no 11 pp 3986ndash3990 2004
[16] S Mutyala M B McDonald K A Scheinblum M D OstrickS F Brint and H Thompson ldquoContrast sensitivity evaluationafter laser in situ keratomileusisrdquo Ophthalmology vol 107 no10 pp 1864ndash1867 2000
[17] J W W Chan M H Edwards G C Woo and V C P WooldquoContrast sensitivity after laser in situ keratomileusis one-yearfollow-uprdquo Journal of Cataract and Refractive Surgery vol 28no 10 pp 1774ndash1779 2002
[18] C Villa R Gutierrez J R Jimenez and J M Gonzalez-Meijome ldquoNight vision disturbances after successful LASIKsurgeryrdquo British Journal of Ophthalmology vol 91 no 8 pp1031ndash1037 2007
[19] A Lorente-Velazquez A Nieto-Bona C V Collar and A GMesa ldquoStraylight and contrast sensitivity after corneal refractivetherapyrdquoOptometry and Vision Science vol 88 no 10 pp 1245ndash1251 2011
[20] A Cervino C Villa-Collar J M Gonzalez-Meijome T Ferrer-Blasco and S Garcıa-Lazaro ldquoRetinal straylight and lightdistortion phenomena in normal and post-LASIK eyesrdquoGraefersquosArchive for Clinical and Experimental Ophthalmology vol 249no 10 pp 1561ndash1566 2011
[21] C McAlinden K Pesudovs and J E Moore ldquoThe developmentof an instrument to measure quality of vision the quality ofvision (QoV) questionnairerdquo Investigative Ophthalmology andVisual Science vol 51 no 11 pp 5537ndash5545 2010
[22] C McAlinden E Skiadaresi and J E Moore ldquoVisual andrefractive outcomes following myopic laser-assisted subepithe-lial keratectomy with a flying-spot excimer laserrdquo Journal ofCataract and Refractive Surgery vol 37 no 5 pp 901ndash906 2011
[23] THiraoka COkamoto Y Ishii T Kakita andTOshika ldquoCon-trast sensitivity function and ocular higher-order aberrationsfollowing overnight orthokeratologyrdquo Investigative Ophthalmol-ogy and Visual Science vol 48 no 2 pp 550ndash556 2007
