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Correlation Of Corneal Contour With Higher Order Ocular Aberrations (HOA) In Indian
Eyes
Manish Chaudhary MSAmit Gupta MS
Advanced Eye Centre, Postgraduate Institute of Medical Education &
Research, Chandigarh
India(Email : [email protected])
The authors have no financial interest in the subject matter of this posterThe authors have no financial interest in the subject matter of this poster
ID 737882
Role of Corneal Contour The anterior corneal surface is the major refractive
component of the human eye and major determinant in quality of optical image
Ideally, cornea must have an optical zone consisting of an elliptical surface with an adequate shape factor (Q factor or asphericity) to minimize curvature induced ocular aberrations and optimal image formation.Calossi A. Corneal Asphericity and Spherical Aberration. J Refract Surg 2007;23:505-514.
Limited literature exists correlating corneal asphericity with ocular aberrations. To the best of our knowledge, this is the first study correlating Higher order ocular aberrations with asphericity of corneal contour.
Study Design: An observational cross sectional prospective study
Study Population Group I : 500 emmetropic eyes (refractive error
0+0.25 D) Group II : 500 myopic eyes (refractive error > -
0.25 to < -6.0 diopters)
Purpose
Patients and Methods
Correlation Of Corneal Contour With Higher Order Ocular Aberrations (HOA) In Indian Eyes
Methods
Exclusion criteria• Corneal degenerations
and dystrophies• Corneal scarring after
infective diseases• Dry eye patients• Any Other ocular
pathology
Patient Workup:Patient Workup:
• Best Corrected Visual Best Corrected Visual
Acuity, Acuity,
• Slit Lamp Biomicroscopy, Slit Lamp Biomicroscopy,
• Refraction, Refraction,
• Schirmer’s test, Schirmer’s test,
• Aberrometry:Aberrometry: Optical Path Optical Path
Difference (OPD) Scanning Difference (OPD) Scanning
done after dilating with done after dilating with
0.8% tropicamide and 5% 0.8% tropicamide and 5%
phenylephrine using ARK-phenylephrine using ARK-
10000 OPD scan (NIDEK 10000 OPD scan (NIDEK
Technologies, Japan)Technologies, Japan)
Inclusion criteria
• Age 18-40 years. • Best corrected visual acuity
(BCVA)of 6/9 or better.• Normal ocular examination,
emmetropia or Myopia < 6 D.
Aberrometric Analysis by OPD Scan
Thibos et al. Standards for reporting the optical aberrations of eyes. J Refract Surg 2002; 18:S652–S660
Aberrometric Data Interpretation and Analysis
Step 1: OPD Scan Analysis Step 2: Zernike polynomials at 6mm transformed into
Step 3: Statistical Analysis ‘t-test’ (for normal Distribution) & for
skewed data Mann- Whitney test. Relationship between different
variables using Spearman and Pearson correlation coefficient
•Root mean square (RMS) of higher order aberration (HOA) from the 3rd to 6th orders
•RMS of the spherical aberration (SA) (square root of the sum of the squared coefficients of Z4 0 and Z6
0),
•RMS of coma (square root of the sum of the squared coefficients of Z3
-1, Z31, Z5
-1,and Z51),
• RMS of trefoil (square root of the sum of the squared coefficients of Z3
-3, Z33, Z5
-3,and Z53
Results Patients characteristics in emmetropic and myopic group
Keratometric values in emmetropic and myopic group
Number of eyes in different subgroups
Group I
(Emmetropic
group)
Group II
(Myopic
groups)
Male 147147 9090
Female 103103 160160
Mean age
(Years)
28.40 28.40 ++ 7.4 7.4 27.82 27.82 + + 5.49 5.49
Group I (Emmetropic
group)
Group II
(Myopic groups)
K1 (diopter) 43.93 + 1.73 44.33 + 2.84
K2 (diopter) 43.25 + 1.61 43.65 + 1.53
Average
(diopter)
43.6 + 1.66 44.06 + 1.57
Prolate (Q < 0)
Oblate (Q > 0)
Emmetropia (no of eyes)
420 80
Myopia
(no of eyes)442 58
Emmetropic group : Emmetropic group : Higher keratometry values (>46 D) were associated with significantly higher amount of total wavefront aberration, total higher order aberrations, 3rd, 5th order as well as trefoil
Comparison of wavefront error and keratometry value in emmetropic eyes
Group Keratometry value Number of eyes
A < 44 diopter 317
B 44-46 diopter 141
C > 46 diopter 42
keratometry value in Emmetropic eyes
Myopic group : Higher keratometry values (>46 D) were associated with significantly higher amount of trefoil
Comparison of wavefront error and keratometry value in myopic eyes
Group Keratometry value Number of eyes
A < 44 diopter 230
B 44-46 diopter 221
C > 46 diopter 49
keratometry value in Myopic eyes
Figure : Distribution of asphericity coefficient (Q) in emmetropic and myopic eyes
Figure : Comparison of asphericity coefficient (Q) value along steep , flat axis and average in emmetropic versus myopic eyes
Distribution of Q value in emmetropic and myopic eyes (prolate versus oblate cornea)
We found most common Asphericity coefficient (Q) value is between 0 to -1 (prolate ellipse) in both the groups
Prolate (Q < 0) Oblate (Q > 0)
Emmetropia
(number of eyes)420 80
Myopia
(number of eyes)442 58
Significance of wavefront aberrations with Corneal Asphericity in emmetropic eyes
Significant association of total HOA, coma, spherical aberration with Oblate cornea in emmetropic eyes
The mean RMS value of total HOAs, coma, and spherical aberration were significantly higher in oblate then prolate corneas
Prolate (mean +SD mm)
Oblate (mean + SD mm)
Significance
( p-value )Total wavefront aberration
0.95 + 0.56 1.48 + 1.81 0.137
Total HOA 0.321 + 0.16 0.37 + 0.14 0.001
2nd order 0.52 + 0.57 0.65 + 0.94 0.686
3rd order 0.14 + 0.09 0.15 + 0.08 0.242
4th order 0.054 + 0.04 0.066+ 0.054 0.078
5th order 0.026 + 0.017 0.027 + 0.025 0.233
6th order 0.0113 + 0.0116 0.012 + 0.016 0.831
Coma 0.082 + 0.053 0.093 + 0.057 0.034
Spherical aberration 0.096 + 0.080 0.125 + 0.107 0.042
Trefoil 0.118 + 0.084 0.116 + 0.078 0.96
Significance of wavefront aberrations with Corneal Asphericity in myopic eyes
Significant association of total HOA, spherical aberration with Oblate cornea in myopic eyes
The mean RMS value of total HOAs and spherical aberration were significantly higher in oblate then prolate corneas
Prolate cornea (mean +SD mm)
Oblate cornea (mean + SD mm)
Significance
( p -value )
Total wavefront aberration
4.60 + 2.76 4.59 + 2.37 0.91
Total HOA 0.49 + 0.46 0.49 + 0.33 0.017
2nd order 2.45 + 1.58 2.03 + 1.38 0.08
3rd order 0.21 + 0.20 0.19 + 0.11 0.163
4th order 0.08 + 0.10 0.09 + 0.08 0.058
5th order 0.038 + 0.046 0.032 + 0.023 0.74
6th order 0.023 + 0.033 0.023 + 0.033 0.1
Coma 0.12 + 0.153 0.11+ 0.07 0.227
Spherical aberration 0.15 + 0.20 0.17 + 0.18 0.005
Trefoil 0.16 + 0.16 0.15 + 0.10 0.58
Emmetropic eyes • Higher keratometric value > 46 diopter was associated with
significantly higher value total wavefront aberration, total HOAs, 3rd order, 5th order as well as trefoil
• We found Oblate corneas (Q > 0) were associated with higher total HOAs, coma and spherical aberration
Myopic eyes • Higher keratometric value > 46 diopter was associated with significantly higher value of trefoil• Oblate corneas (Q > 0) were associated with higher total HOAs and spherical aberration
Our study highlights the association of corneal asphericity with HOA Higher keratometric (>46 D) and oblate cornea were associated with significantly higher amount of HOAs