British Journal of Ophthalmology, 1984, 68, 97-104 Astigmatism following cataract surgery VERONICA M. READING From the Department of Visual Science, Institute of Ophthalmology, Judd Street, London WCI H 9QS SUMMARY The changes in corneal curvature were determined at regular intervals over a one-year period following intracapsular cataract extraction by microsurgical techniques. During the first postoperative month photokeratometric measurements showed rapid changes in astigmatism associated with large changes in the direction of the axis. Thereafter astigmatism against-the-rule predominated. Data from the small group of patients who underwent surgery in which the technique of phacoemulsification was used show that the smaller changes in corneal curvature are attributable to the smaller incision size and reduced number of sutures. With patients who underwent intracapsular extraction a comparison has been made between the effects of large and small section sizes, and a procedure is outlined whereby surgically induced astigmatism may be minimised. Donders' first showed that an unwelcome con- sequence of cataract surgery is an alteration in corneal curvature. Studies on corneal astigmatism related to intracapsular cataract surgery have been numerous (for a comprehensive review of the work since 1941 see Funder et al.2). The older surgical techniques started without sutures at the turn of the century. Both these and later techniques employing one or 2 large gut sutures caused a predominance of astigmatism against-the-rule. This was due to the 'wound gaping or stretching vertically, which increased the circumference of the globe, causing a flattening in this meridian. In addition there was steepening of the horizontal meridian. In the past decades there has been increasing use of the operating microscope for cataract surgery. At a congress in 1969 an audience poll showed 3% using this instrument, in 19713 the figure was 30%; in 19754 83% used it routinely or occasionally; by 19781 it was de rigueur. Together with the development of finer suture materials surgeons now have far greater control over the optical outcome of the operation. However, there are widely disparate views on the causes and correction of postoperative astigmatism. They relate mainly to the methods of incision and closure and the effects on corneal curvatures. There is controversy over the incision size and location, the depth of sutures, the material, and the technique of suturing. There is evidence that the more peripheral the section the less effect there is on surgically Correspondence to Dr V. M. Reading. induced astigmatism.6 (Troutman's7 use of a '160° corneal incision and use of 10-0 nylon sutures through the full thickness of the wound' apparently gives similar optical results.) Changes attributable to the suture material have been observed,8 9 as has a rotation in the axis of astigmatism. 10 Singh and Kumar" found no appreciable difference between surgically induced astigmatism with pre- or post- placed sutures. The results of phacoemulsification show that within one month of surgery the mean induced astigmatism is less than 0-5 D. 12-15 The present investigation examined the effects on surgically induced astigmatism of one routine incision and closure technique with microsurgical techniques and a fine suture material. The aim, therefore, was to analyse the magnitude and duration of the changes in corneal curvature, induced by intracapsular extrac- tion, over a one-year period. In addition a parallel study was done on patients who had undergone extraction by the technique of phacoemulsification, on the asumption that smaller changes may occur owing to the small incision size and reduced number of sutures. Materials and methods Patient sample. The total number of eyes in the intracapsular cataract extraction series was 37 (36 patients). Their ages varied from 53 to 94 years, mean 75 yr (standard error 1.4). In the phacoemulsification series the number of eyes was 6, in the age range 48-77 years, mean 62-2 yr (standard error 3.8). 97 on May 30, 2020 by guest. Protected by copyright. http://bjo.bmj.com/ Br J Ophthalmol: first published as 10.1136/bjo.68.2.97 on 1 February 1984. Downloaded from
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British Journal ofOphthalmology, 1984, 68, 97-104
Astigmatism following cataract surgery
VERONICA M. READING
From the Department of Visual Science, Institute ofOphthalmology, Judd Street, London WCIH 9QS
SUMMARY The changes in corneal curvature were determined at regular intervals over a one-yearperiod following intracapsular cataract extraction by microsurgical techniques. During the firstpostoperative month photokeratometric measurements showed rapid changes in astigmatismassociated with large changes in the direction of the axis. Thereafter astigmatism against-the-rulepredominated. Data from the small group of patients who underwent surgery in which thetechnique of phacoemulsification was used show that the smaller changes in corneal curvature areattributable to the smaller incision size and reduced number of sutures. With patients whounderwent intracapsular extraction a comparison has been made between the effects of large andsmall section sizes, and a procedure is outlined whereby surgically induced astigmatism may beminimised.
Donders' first showed that an unwelcome con-sequence of cataract surgery is an alteration incorneal curvature. Studies on corneal astigmatismrelated to intracapsular cataract surgery have beennumerous (for a comprehensive review of the worksince 1941 see Funder et al.2). The older surgicaltechniques started without sutures at the turn of thecentury. Both these and later techniques employingone or 2 large gut sutures caused a predominance ofastigmatism against-the-rule. This was due to the'wound gaping or stretching vertically, whichincreased the circumference of the globe, causing aflattening in this meridian. In addition there wassteepening of the horizontal meridian. In the pastdecades there has been increasing use of theoperating microscope for cataract surgery. At acongress in 1969 an audience poll showed 3% usingthis instrument, in 19713 the figure was 30%; in 1975483% used it routinely or occasionally; by 19781 it wasde rigueur. Together with the development of finersuture materials surgeons now have far greatercontrol over the optical outcome of the operation.However, there are widely disparate views on the
causes and correction of postoperative astigmatism.They relate mainly to the methods of incision andclosure and the effects on corneal curvatures. There iscontroversy over the incision size and location, thedepth of sutures, the material, and the technique ofsuturing. There is evidence that the more peripheralthe section the less effect there is on surgically
Correspondence to Dr V. M. Reading.
induced astigmatism.6 (Troutman's7 use of a '160°corneal incision and use of 10-0 nylon sutures throughthe full thickness of the wound' apparently givessimilar optical results.) Changes attributable to thesuture material have been observed,89 as has arotation in the axis of astigmatism. 10 Singh andKumar" found no appreciable difference betweensurgically induced astigmatism with pre- or post-placed sutures. The results of phacoemulsificationshow that within one month of surgery the meaninduced astigmatism is less than 0-5 D. 12-15The present investigation examined the effects on
surgically induced astigmatism of one routine incisionand closure technique with microsurgical techniquesand a fine suture material. The aim, therefore, was toanalyse the magnitude and duration of the changes incorneal curvature, induced by intracapsular extrac-tion, over a one-year period. In addition a parallelstudy was done on patients who had undergoneextraction by the technique of phacoemulsification,on the asumption that smaller changes may occurowing to the small incision size and reduced numberof sutures.
Materials and methods
Patient sample. The total number of eyes in theintracapsular cataract extraction series was 37 (36patients). Their ages varied from 53 to 94 years, mean75 yr (standard error 1.4). In the phacoemulsificationseries the number of eyes was 6, in the age range48-77 years, mean 62-2 yr (standard error 3.8).
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carried out by 3 surgeons using similar techniqueswith the Zeiss Mark 6 operating microscope. Thepatients were under general anaesthesia. In brief theintracapsular surgical technique involved making (1)a limbus based conjunctival flap; (2) a 2-step comeo-scleral incision, located at the posterior margin of thelimbus, into the anterior chamber; (3) singleiridectomy at about 12 o'clock; (4) weakening thezonule with 5% alpha-chymotrypsin; and (5)removing the cataract with an Amoils cryoprobe.Two of the surgeons used two preplaced 8-0 virginsilk sutures after making the initial incision and thencompleted the incision with scissors. The thirdsurgeon used 2 postplaced sutures. The sutures wereplaced to a depth of two-thirds of the corneal tissue.After removal of the cataract further cornealscleralsutures were inserted as was felt necessary.
Surgeon A performed 18 extractions, cutting a
section size between 120-139° in 11 cases andfavouring the use of 3 sutures. Surgeon B performed13 extractions, within an evenly distributed range ofsection size from 110 to 1600, on 7 cases, inserting 4sutures. Surgeon C used a larger incision, 140-160°,in his 6 extractions.The phacoemulsification technique involved (1)
making a limbus-based flap; (2) entering the anteriorchamber in one stroke with a Pearce-Hoskins knife;(3) incising the anterior capsule with a keratome; (4)prolapse of the lens nucleus into the anteriorchamber; (5) emulsification with the KelmanCavitron phacoemulsifier; (6) removal of the corticalremnants by irrigation and aspiration; (7) making asmall peripheral iridectomy; and (8) closure of thewound with one 8-0 virgin silk suture. Silk was alsoused to close the conjunctival flap.
In all cases, after the wound had been satisfactorilyclosed, but before the conjunctival flap had beensutured, one eyepiece of the operating microscopewas replaced with another containing a protractorgraticule. The magnification of the zoom lens wasadjusted until the graticule just overlay an image ofthe limbus. The section angular size and suturepositions were measured, all by the same person.
Keratometry. A photokeratometer was used.Because even the physiological cornea is not a trulyspherical surface, alignment of the eye and opticalsystem is always critical. A fixation target waspresented to ensure that the same part of the cornea
was always examined. Use of subsidiary illuminationenabled us to film the pupil and iris with such contrastas to be able to identify frames showing misalignmentcaused by poor fixation of the patient. These wererejected. The magnification of the keratometer was
determined with a millimetre scale. The cornealcurvature was calculated from projection of the
frames and the geometry of the situation. The sameperson measured all the film frames, thus minimisingthe personal error. Measurements were made in thehorizontal, vertical, and 2 oblique meridians withinthe optical, zone (1 5 mm corneal section) and in amore peripheral region (4mm corneal section).Photokeratometry was carried out preoperatively,
one and 2 weeks after surgery, one month post-operatively, thereafter monthly for 9 months, andfinally at one year after surgery. Where possiblemeasurements were also taken of the nonoperatedeyes at each visit as controls. In addition data wereobtained from 4 young adults with normal vision.
Results
Intracapsular extractions. The subdivision of the datainto categories according to incision size and numberof sutures is shown in Table 1. Because of the smallsamples, a comparison of the keratometric resultsobtained for a particular section size and set numberof sutures would not be statistically valid.
Meridian of corneal astigmatism. Preoperatively53% of the patients had astigmatism against-the-rule(i.e., the meridian of maximum power washorizontal), and, as most of the patients were elderly,this is in accord with the senile changes in cornealastigmatism. 16 One week postoperatively the 2principal meridians were randomly distributed, butthereafter the steeper curvature of the horizontalmeridian not only reasserted itself but was evidencedin 80% of the sample. Conversely, in similar pro-portions the vertical meridian was flattest, i.e.,mirror-imaging the meridian of steepest curvature.
Changes in the radii of curvature. Fig. 1 shows themean radii of curvature of the corneal cap during thepostoperative period. Taken in conjunction withTable 2 it can be seen that the mean values maskother types of change which occurred (Fig. 2). Casesare shown where the radius in one meridiandecreased while the other increased (Figs. 2A and C),where both increased (Fig. 2B), and where bothdecreased (Fig. 2D). The 'classical' postoperative
Table 1 Intracapsular extraction sample, subdivided onincision size and number ofsutures
astigmatism, where the horizontal radius decreasedand the vertical radius increased, was found in only6-5% of the sample immediately postoperatively,though it was present in 42 3% of the patients by thefirst postoperative month.Comparison of the pre- and postoperative radii for
each meridian showed a high positive correlation.Paired t test analyses showed no significant dif-ferences in a comparison of data of the left and rightoblique meridians. In the horizontal meridians mostof the pre- and postoperative mean values differedsignificantly (p<0O01) up to 12 postoperative months;
Table 2 Intracapsular extractions. Percentage distributionofthe groups showing the 4 types ofsurgically inducedastigmatism, categorised one week postoperatively. Alsotabulated are the mean power differences in the horizontal(DH) and vertical (Dv) meridians (i.e., preoperative powerminus the power one week postoperatively)
Percentage ofsample where the radius ofcurvature in thePostop. H inc H inc H dec H decperiod V dec V inc V inc V dec
Fig. I Intracapsular extractions.The mean radii ofcurvature in eachof the 4 meridians ofthe cornealcap, during the postoperativeperiod. Zero on the abscissa refersto the mean radii preoperatively.
in the vertical meridian the data were not significantlydifferent from 5 postoperative months onwards.The more peripheral corneal region (i.e., 4 mm
corneal section) showed smaller changes (Fig. 3).Pre- and postoperative data in 3 of the meridiansstudied, namely, the 2 obliques and vertical, were notsignificantly changed, even immediately post-operatively. Pre- and postpaired data did differ in thehorizontal meridian but only up to the first post-operative month.
Influence ofsection size and number ofsutures. Themean postoperative radii of curvature, where thesection size was smaller (100-129°) with 3 sutures andlarger (140-160°) with more than 3 sutures respect-ively, are shown in Fig. 4. The smaller section sizedata showed statistically significant changes up to theeighth postoperative month in the vertical meridian,whereas the results differed from the preoperativevalues only up to one month postoperatively in thehorizontal meridian. Thus the radius of curvature inthe vertical meridian increased, apart from the earlypostoperative changes, and furthermore this comealflattening persisted. Conversely, the mean data of thepatients who had the larger section showed littlevariation in the vertical meridian, but steepening ofthe curvature in the horizontal meridian which was
still statistically significantly different from the pre-
operative state one year later.Phacoemulsification. During the 2-year period of
this study 6 patients underwent cataract surgery by
phacoemulsification. The smaller variation in themean radii of curvature (Fig. 5) lend weight to theassumption that postoperative changes would besmaller than comparable intracapsular data.
Direct comparison of the 2 techniques. Patient ABpresents an example of the 2 techniques. The rightextraction was intracapsular, incision size 1550 andclosed with 4 comeoscleral sutures. The left lens wasremoved by phacoemulsification, section size 250 withone centrally placed suture. The same surgeonoperated on both eyes within one week. The results
8 0
7 5
Fig. 3 Intracapsular extractions.The mean radii ofcurvature in the 4meridians in the more peripheralcorneal section, as afunction oftime postoperatively.
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(Fig. 6) show the much larger changes that occurredin corneal curves following the intracapsular extrac-tion, i.e., a large section as opposed to a small one.Preoperatively the comeal astigmatism was 1-41 D inthe right eye, 1-37 D in the left, the horizontalmeridian being the most powerful in each case. Table3 gives the results at the postoperative periods of oneweek and one year. They show that immediately afteroperation the phacoemulsification operation hadcaused an increase that was less than 50% of thatinduced by intracapsular extraction. After one year
INTRACAPSULAR EXTRACTION
1,I IJHorizontal
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POSTOPERATIVE PERIOD (MONTHS)
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horizontal and vertical mean radii44 r) ofcurvature and dioptric power,4 2 0 measured at the corneal cap, of the43 * sample where the incision size was
;O 100-129' (top 2 Figures) and where4 4 the incision size was larger,
140-160° (lower2 Figures).40
41
4243
POSTOPERATIVE PERIOD (MONTHS)
the left and right eyes had induced astigmatism of 0-5D and 1 85 D respectively.
Control data. No significant changes occurred incorneal curvature in the sample of control data, eitherin the group consisting of patients' unoperated eyesor in the 'normal' group.
Discussion
In the patients who underwent intracapsular cataractextraction surgery has significantly increased thenumber of those in whom astigmatism against-the-rule predominates in the long term, as compared withtheir preoperative condition. The mean values of theradii (Fig. 1) in the horizontal meridian initially showa flattening followed by a steepening up to one monthafter the operation, and thereafter tend to remainstable although steeper than the preoperative state.The radii in the vertical meridian mirror-image thehorizontal but revert almost to the preoperative
Table 3 Comparison ofastigmatism ofpatient in Fig. 6.Intracapsular extraction in right eye, phacoemulsification inleft eye
values. Apart from the immediate postoperativechanges, little of consequence occurred in the obliquemeridians. Analysis of the mean values of the radii inthe horizontal and vertical meridians revealedchanges other than those shown in Fig. 1 (Table 2).Thus both radii of the major meridians may increase,or decrease, or one increase while the other decreases(Fig. 2). 'Classical' astigmatism, where the horizontalradius decreases and the vertical radius increases, waspresent in only 6&5% of the sample immediately post-operatively but increased to 42-3% by one month.One may postulate that the large changes in
curvature, shown in Figs. 2A and C, may be the resultof excessive tissue handling during suturing, resultingin more postoperative oedema than in groups B andD; it was not associated with the work of a particularsurgeon.A paired comparison of the preoperative and
resultant astigmatism in the patients who had intra-capsular extraction showed significant differences atall serial intervals. However, analyses of the pairedsamples one month vs. 3 months, one month vs. 6months, and so on, were not significant. Thisindicates that, although the corneal contours wouldnot resume preoperative values, changes occurringafter one month were small. Furthermore, the paireddata 1 week vs. 2 weeks postoperatively were
statistically different from zero (p<002), but notsignificant for 2 weeks vs. 1 month.
Studies on the placement of sutures used in cornealincisions have shown that it is advantageous to placesilk sutures at midstromal level, as more deeplyplaced sutures can lead to necrosis of the tissue and
* .Horizontal meridian
0
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/O Horizontal meridian
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Fig. 5 Phacoemulsificationextractions. The mean radii ofcurvature in each of the 4meridians, during the postoperativeperiod. Zero on the abscissa refersto the mean radii preoperatively.
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POSTOPERATIVE PERIOD ( MONTHS)
proliferation of epithelium along the suture tract.'7However, Flaxel and Swan's'9 histological exam-ination of human post-mortem material has demon-strated that, after cataract extraction, limbal woundsunder limbal-based flaps heal by ingrowth of the sub-epithelial connective tissue between the stromal
wound edges. This ingrowth begins by 8 days and iscomplete, in that it extends through the entirethickness of the wound, about 15 days after surgerythough the limbal wound is still weak. Thus the factthat the first signs of stability of the corneal curvaturein this sample was demonstrated at 2 postoperative
PATIENT: AB
Fig. 6 Mean radii ofcurvature ofthe left and right eye ofpatient A Bduring the postoperative period.The incision sizes and positions ofthe sutures are shown in the insets.Filled and unfilled symbols refer tothe horizontal and vertical radii ofcurvature respectively. Left eye:phacoemulsification (squares).Right eye: intracapsular extraction(circles).
Left eye Phacoemulsification
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POSTOPERATIVE PERIOD (MONTHS )
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weeks may result from the completion of thisingrowth.
Use of alpha-chymotrysin. Kirsch20 performedpostoperative Schi@tz tonometry and found that atransient rise in intraocular pressure may occur, withthe greatest rise usually on postoperative days 2 to 5and of average duration 7 days. Such a rise mayaccount for some of the early postoperative changes,since a raised intraocular pressure can reasonably beexpected to interfere with wound apposition. Kirsch2'has further shown that wound healing problems occuralmost 3 times more frequently in cases where alpha-chymotrysin is used than in a parallel control group.Soll22 gives an incidence of between 50 and 60%.
Use of virgin 8-0 silk suture material. When alpha-chymotrysin is used the tensile strength of virgin silkis reduced by 20-25% between the second and thefourteenth days.23 This may result in a stretchingeffect which could cause slight misalignment of thesection. Pearce24 compared postoperativeastigmatism with the use of different suture materials,indicating that there is a reduction in the astigmatismfrom 1-72 D with virgin silk to 0 9 D with mono-filament nylon. Similar results were obtained byWyman.25 This variation in performance mayaccount for some of the changes observed in thepresent series.Of interest is the patient who had an intracapsular
extraction in one eye and phacoemulsification in theother (Fig. 6). The indications here are that with asmall section, a single suture, and minimal tissuehandling the resultant changes in curvature arereduced.Comparison of the data concerning the effect of
section size and consequent number of suturesprovides a clue to the surgical control of astigmatism.In cases where the smaller section was made,100-1290, it was the curvature of the verticalmeridian which became flatter than the preoperativestate and remained so, whereas in the horizontalmeridian the radius did not vary appreciably.Conversely, cases where a larger section was cut,140-160°, and more sutures used, the curvature in thevertical meridian varied little, but the steeperhorizontal steepened and tended to remain steeperthan in the preoperative state. These long-termchanges on comeal curvature may most easily beexplained by the process of crimping. When con-sidering a large section, it is as if one were placing theindex finger and thumb at 3 o'clock and 9 o'clockrespectively on the limbus, and gently pinching. Thishas the effect of steepening the curvature in thehorizontal meridian, with little effect on the vertical.With small section sizes as well as phacoemulsifica-tion the pinching effect will have less of a purchaseand consequently less effect on corneal curves.
One might suggest that cataract surgery wouldcause minimal change in comeal curvature, or evenpurposely induce surgical astigmatism in order toreduce the pre-existing astigmatism, if the followingprocedure were followed. Prior to surgery the corneashould be measured keratometrically to determinethe amount and axis of astigmatism. The best incisionto use in order to minimise postoperative surgicallyinduced astigmatism can then be determined. Thesmaller incision will have a tendency to flatten thecurvature of the meridian about which the incision iscentred, whereas the effect of the larger incision is toincrease the curvature in the meridian at right-anglesto the centre of that incision. Thus the orientation ofthe incision, its size, and the consequent number ofrequired sutures could be adjusted in an attempt togive the optimum result. Since the net result with theusual superior incision is to produce astigmatismagainst-the-rule, to a lesser or greater degree patientswith astigmatism with-the-rule before the operationhave the advantage. This may partly explain theexcellent postoperative results of Kelman's 14phacoemulsification study, since of the 500 casesexamined 73% were under 60 years of age. Themajority of patients undergoing intracapsularextraction are elderly, in whom preoperativeastigmatism against-the-rule predominates. Never-theless, if the surgeon were willing to cut a sectiontemporally if necessary, he could determine themeridian of greatest curvature and centre the incisionin that region. A small incision would probably causea flattening in that meridian, thereby lessening thepower to match the least curved meridian. A largeincision would have the effect of steepening thepreviously flattest meridian, thereby increasing thepower. Control of such astigmatism would be ofbenefit to the patient whether he is fitted withspectacles, contact lenses, or intraocular lens implant.Thanks are due to the consultants who referred patients andparticularly to Mr V. N. Highman, then at the Charing CrossHospital (Fulham), London, who took the measurements duringsurgery. Some of the equipment was purchased with a grant from theUniversity of London Central Research Fund.
References
I Donders FC. On the anomalies ofaccommodation and refractionofthe eye. London: New Sydenham Society, 1864: 334.
2 Funder W, Havelec L, Stierschneider H. Der postoperativeHornhautastigmatismus, ein Problem der Staroperation. KlinMonatsbl Augenheilkd 1974; 165: 244-58.
3 Troutman RC. The operating microscope, an essential ingredientof modern cataract techniques? In: Emery JM, Paton P, eds.Current concepts in cataractsurgery. St Louis: Mosby, 1974:16-7.
4 Panel discussion. In: Emery JM, Paton P, eds. Current concepts incataract surgery. St Louis: Mosby, 1976: 31.
5 Troutman RC. Microsurgery now and in the future. DocOphthalmol Proc Ser 1979; 21: 87-90.
6 Jaffe NS. Cataract surgery and its complications. St Louis: Mosby,1976: 83-98.
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20 Kirsch RE. Glaucoma following cataract extraction associatedwith use of alpha-chymotrypsin. Arch Ophthalmol 1964; 72:612-20.
21 Kirsch RE. Further studies on glaucoma following cataractextraction associated with the use of alpha-chymotrysin. TransAm Acad Ophthalmol Otolaryngol 1965; 69:1011-23.
22 Soil DB. In: Emery JM, Paton D, eds. Current concepts incataract surgery. St Louis: Mosby, 1976: 369.
23 McPherson SD, Crawford R, Moore L, Michels R. Investigationsof corneal suture material. Adv Ophthalmol 1970; 22: 49-57.
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