of axial length and preoperative astigmatism to induced post-operative

Transcription

1 ASTIGMATISM AND VISUAL RECOVERY AFTER 'LARGE INCISION' EXTRACAPSULAR CATARACT SURGERY AND 'SMALL' INCISIONS FOR PHAKOEMULSIFICATION* BY Lei Zheng, MD, John C. Merriam, MD, AND Marco Zaider, PhD ABSTRACT Purpose: This study compares the change over time of the astigmatism caused by "large" incision extracapsular cataract extraction (ECCE) and three smaller incisions for phakoemulsification. Based on this data, a mathematical model that predicts the course of astigmatism after a superior incision of length 3 to 12 mm has been developed. The relationship of axial length and preoperative astigmatism to induced post-operative astigmatism, the recovery of visual acuity, and the rate of YAG laser capsulotomy after each procedure also are documented. Methods: Induced astigmatic change was calculated using a simple method of vector analysis. The change in induced astigmatism was calculated for 8 years after ECCE (n= 144), for 3 years after 6 mm superior incisions (6SUP) (n=93), for 2 years after 3 mm superior incisions (3SUP) (n=12), and for 18 months after 3 mm temporal incisions (3Temp) (n=65). Plotted semi-logarithmically, the astigmatic change in each group may be represented mathematically. Results: Two weeks after ECCE the mean induced cylinder was D, which decayed to about D after 6 months. Induced cylinder increased gradually to about -1.6 D after 8 years, although this further change was not significantly different than that at 6 months after surgery. For the phako groups, the net induced cylinder on the first post-operative day was: D (6SUP), +.49 D (3Sup), and -.19 D (3Temp). After 6Sup the wound was astigmatically stable after approximately 3 months, and 3 years after surgery net induced cylinder was -.66 D. After 3Sup the wound was astigmatically stable after about 6 weeks, and after 18 months net induced cylinder was -.35 D. No significant change in astigmatism was detected at any time after 3Temp. Maximum visual acuity was reached after a mean of approximately 6 weeks after ECCE, 2 weeks after 6Sup, and between 1 day and 1 week after 3Sup and 3Temp. The rate of 'From the Edward S. Harkness Eye Institute (Dr Zheng and Dr Merriam) and the Department of Radiation Oncology (Dr Zaider), College of Physicians and Surgeons, Columbia University, New York. TR. AM. OPHTH. SOC. VOL. XCV, 1997

2 388 Zheng et al YAG laser capsulotomy was higher after ECCE than after any of the phakoemulsification procedures. No relationship of axial length or preoperative astigmatism to astigmatic change was detected. Conclusions: Incision size and location affect post-operative astigmatism. Induced astigmatism decreases with wound size, and only the 3 mm temporal incision is astigmatically neutral. The time for visual recovery increases with wound size. There appears to be less need for laser capsulotomy after phakoemulsification with capsulorrhexis than after ECCE. Axial length does not affect induced astigmatism after any of the 4 incisions, and preoperative astigmatism does not affect astigmatic change after ECCE and 6Sup. INTRODUCTION The rate of change in methods of cataract surgery in the late 2th century has been far more rapid than at any other time. The exact time when couching began is not known with certainty, but this simple technique probably was practiced 5 years before Christ, and perhaps even earlier. Couching survived in the Western world until the early 19th century and was practiced on the Indian subcontinent, where it may have originated, until the early 2th century. Thus couching was used to relieve cataract blindness for perhaps 2,5 years! Extraction began to be a common practice in the early 19th century in the West. During this period, sutures, needles, and anesthetics were introduced and refined. Because opacification of the capsule required a second invasive procedure to restore vision, intracapsular surgery became the favored technique. Initially practiced with loupes and a forceps or erisophake, intracapsular surgery became safer and more precise with use of the cryoprobe, alpha-chymotrypsin, and the operating microscope. In the last 2 years, the development of anterior and posterior chamber intraocular lenses, phakoemulsification, and the YAG laser has led to the rapid reemergence of extracapsular surgery via smaller and smaller incisions.1-39 The era of "large incision" cataract extraction, which lasted about 2 years, is over. This paper compares a single surgeon's experience with extracapsular cataract extraction (ECCE) and three "small" incisions for phakoemulsification and presents a model of the course of postoperative astigmatic change. METHODS From patient charts the following information was extracted: age and sex (Table I), axial length (Table II), date and type of procedure, intraocular

3 Astigmatism After Phakoemulsification 389 TABLE I: PATIENT DATA INCISION PATIENT EYES MEAN AGE (SD) FEMALES MALES OD OS ECCE (1.1) Sup (9.7) Sup (9.7) Temp (8.9) lens (IOL) style, incision length and location, use of sutures, keratometry, visual acuity, refraction, date of laser capsulotomy, and complications. Only cases with at least three postoperative measurements of visual acuity and keratometry were included in this review. The author has used various incisions and IOLs, but the review was limited to four standard techniques: ECCE, 6.-mm superior scleral tunnel (6Sup), 3.-mm superior scleral tunnel (3Sup), and 3.-mm temporal scleral tunnel (3Temp). Generally, a postoperative refraction of plano to -.75 diopters was the goal, and cylinders were recorded in "plus" form. All procedures were performed with local anesthesia with 2% xylocaine and.75% marcaine. ECCE The globe and orbit were decompressed for 15 minutes prior to surgery. After creation of a fornix-based conjunctival flap, a partial-thickness, posterior limbus incision was made superiorly for approximately 16. A double-armed 8- black silk suture was passed across the wound nasally and temporally prior to enlarging the wound. An anterior capsulotomy was performed with a bent needle and scissors. Except for 4 eyes with high axial myopia, an IOL was used in all cases. A flexible anterior chamber (AC) IOL was placed in 1 eye after capsular rupture and anterior vitrectomy; a polymethylmethacrylate (PMMA) posterior chamber (PC) IOL with an optic of 6, 6.5, or 7 mm was used in the remaining eyes. The preplaced silk sutures were cut and tied, and the wound was closed with additional interrupted sutures of 1- nylon. PHAKOEMULSIFICATION A fomix -based conjunctival flap was used with all incisions in this review, and all scleral tunnels were begun approximately 1.5 mm posterior to the limbus. After creation of a continuous tear capsulorrhexis, the nucleus was removed with a standard four-quadrant, "divide and conquer" technique. The IOL was placed in the capsular bag. The 6.-mm scleral tunnel was closed with 2 interrupted sutures of 1- nylon. The superior and temporal 3.-mm short scleral tunnels were not sutured or were closed with a single radial 1- nylon suture. Posterior chamber PMMA IOLs with a 6- mm optic were used with the 6-mm incision, and foldable silicone IOLs were used with the 3-mm incisions.

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5 Astigmatism After Phakoemulsification 391 COMPLICATIONS The posterior capsule was broken intraoperatively in 2 cases each in the ECCE (1.4%) and the 6Sup (2.2%) groups, in 1 case in the 3Sup group (.8%), and in no cases in the 3Temp group. The incidence of capsular rupture and anterior vitrectomy in the entire series was 1.6%. There were no complications from anesthesia. No patient suffered acute or delayed endophthalmitis or developed corneal edema or an inadvertent filtering bleb during follow-up with the surgeon. A 63-year-old woman had a spontaneous retinal detachment 6 months after uncomplicated phakoemulsification OD via a 6-mm incision. Although the macula was detached, she recovered 2/2 acuity after pneumopexy. Six weeks after pneumopexy, she developed a new retinal break, was treated with a 5-mm sponge explant, and was subsequently lost to follow-up. A 67-yearold man, who had had an ECCE and anterior vitrectomy OD with a 7.- mm PMMA IOL 5 years before, fell at home, rupturing the globe along the cataract incision and expelling the IOL. Repair involved vitrectomy, an encircling band, and silicon oil. The aphakic eye now is comfortable with an acuity of "hand motions." (Dr Hermann Schubert performed the retina surgery for these patients.) Clinically significant macular edema was noted in only 1 patient in this series. An 81-year-old woman with narrow-angle glaucoma and exfoliation OD had an ECCE with anterior vitrectomy and AC IOL. Corrected acuity was 2/25 2 months after surgery. Five years later it deteriorated to 2/12 owing to cystoid macular edema associated with a branch retinal vein occlusion. After focal laser therapy, the acuity improved to 2/6. CALCULATION OF ASTIGMATISM Cormeal astigmatism was measured with a keratometer. Only values with axes at the 9' and 18' meridians were included. Because of the normal clinical variability of keratometric measurement, all axes within 1' of 9' and 18' were designated to be either 9' or 18. At any time t before or after surgery, astigmatism was taken as the algebraic difference between the keratometric reading at 9 and that at 18, irrespective of which was larger. With this convention, a positive value means that the 9 meridian is greater, and conversely a negative value means that the 18' meridian is greater. For example, if the keratometry readings at time t1 are 44 at 9' and 42 at 18', the initial corneal astimatism Al is +2. diopters. If at some later time t2, the values are 42 at 9 and 44 at 18', the corneal astigmatism A is -2. diopters. The net change C in comeal astigmatism is C = A2 - Al, or C = (+2.) = -4. diopters. This convention, which may be unfamiliar to clinicians accustomed to using "plus" or "minus" cylinder notation for refraction, permits both the change in magnitude and direction of cormeal astigmatism to be described in a consistent fashion.

6 392 Zheng et al STATISTICAL ANALYSIS The results in the Tables are shown as means and standard deviations. The t-test was used to determine when two independent results with known standard deviations differed at the 95% confidence level (P <.5). RESULTS ASTIGMATISM Postoperative astigmatism was plotted semilogarithmically for each incision (Table III, Figs 1 through 5). ECCE When the 12-month data are used as the benchmark, induced corneal astigmatism becomes stable between 5 and 6 months after a "large incision" ECCE. Induced comeal astigmatism at 12 months differed from that at 5 months after surgery but not that at 6 months after surgery (Table III, Figs 1 and 4). Although the data suggest that a slow ATR drift may occur after 6 months, at the 95% confidence level the data do not prove this conclusion. The postoperative astigmatic change in eyes with preoperative WTR did not differ significantly from that in eyes with ATR astigmatism (Table IV). 6Sup When the 36-month data are used as the benchmark, induced corneal astigmatism becomes stable between 2 and 4 months after a 6.-mm superior scleral tunnel (Table III, Figs 2 and 4). Induced corneal astigmatism at 36 months differed from that at 2 months after surgery but not that at 4 months after surgery. This group also was subdivided into those with preoperative WTR or ATR astigmatism (Table IV). The induced astigmatism of these 2 subgroups is significantly different only at month 4 after surgery. 3Sup When the 24-month data are used as the benchmark, induced corneal astigmatism stabilized between 4 and 6 weeks after surgery (Table III, Figs 3 and 4). Induced corneal astigmatism at 24 months differed from that at 4 weeks after surgery but not that at 6 weeks after surgery. Nearly all the patients in this group had WTR astigmatism preoperatively. The induced astigmatism of wounds closed with a single radial suture (n=27) differed significantly from those left unsutured (n=93) only at 4 weeks after surgery (Table V).

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8 394 Zheng et al u) Q) *, Weeks post-op FIGURE 1 Semi-logarithmic plot of postoperative change in induced comeal astigmatism after ECCE Q-~ a1 12 1~ D Weeks post-op FIGURE 2 Semi-logarithmic plot of postoperative change in induced corneal astigmatism after 6-mm superior scleral tunnel incision. lb3

9 Astigmatism After Phakoemulsification U) o Weeks post-op FIGURE 3 Semi-logarithmic plot of postoperative change in induced corneal astigmatism after 3-mm superior scleral tunnel incision. U) co ;._ d Weeks post-op FIGURE 4 Semi-logarithmic plots without standard deviation. Solid curve: ECCE. Dashed curve: 6- mm superior scleral tunnel incision. Dotted curve: 3-mm superior scleral tunnel incision.

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12 398 Zheng et al 3Temp When the 12-month data are used as the benchmark, no significant change in corneal astigmatism was detected at any time after surgery (Table III, Fig 5). All eyes had ATR astigmatism preoperatively. The induced astigmatism of wounds closed with a single radial suture (n=27) differed significantly from those left unsutured (n=38) only at 4 months after surgery (Table V). MODEL OF ASTIGMATIC CHANGE To compare different procedures, it may be useful to represent the data mathematically. The empirical expression below was derived originally for the postoperative change in induced astigmatism during the first 2 years after ECCE.4' It reproduces the initial and final plateaus and the characteristic decay between them (Figs 1 through 4): D(t) = D -(D-Df) e tb (1) D(t) is the diopters of induced corneal astigmatism at time t after surgery, and D. and Df are the initial and final values of D(t). The parameters a and ft determine with D. and Df the descending portion of D(t). Best-fit values of these parameters are shown in Table VI and are plotted as a function of incision length in Figs 6 and 7. With these, the expression in Eq(1) predicts average diopters of induced astigmatism as a function of time. By linear interpolation, one can obtain values for these parameters for any incision length L between 3 and 12 mm (the value assumed to be the arc length of an ECCE incision). For example, the final induced astigmatic change after a superior incision of length L (6 < L < 12) may be estimated as: D (12) -D (6) D(L)z D(6) + f f (L - 6) (2) For L = 9 mm, interpolation yields the following result: (-.63) D/9)z (9-6) (3) 12-6 D/9) z z -1.1 diopters. VISUAL RECOVERY Only eyes with corrected acuity of 2/4 or better after surgery were included in this portion of the review (Table VII). Reasons for exclusion included macular degeneration, optic atrophy, diabetic retinopathy, amblyopia, and traumatic scars. Figure 8 illustrates the improvement in acuity during the initial 2 months after surgery. Since the visual recovery

13 Astigmatism After Phakoemulsification U2 Q *, {I i {{ l-1 " I1i Weeks post-op FIGURE 5 Semi-logarithmic plot of postoperative change in induced comeal astigmatism after a 3-mm temporal scleral tunnel incision. TABLE VI: PARAMETERS FOR MODEL OF POSTOPERATIVE ASTIGMATISM INCISION Di Df a, ECCE Sup Sup

14 Zheng et al ' :: [ II I nc is ion length / mm FIGURE 6 Solid line: Best fit values of initial diopters of induced corneal astigmatism (D) as a function of incision length. Dotted line: Best fit values of final diopters of induced corneal astigmatism (Dd) as a function of incision length. (Note that -Df is plotted.) Inc is ion length / mm FIGURE 7 Solid line: Semi-logarithmic plot of parameter a as a function of incision length. Dotted line: Semi-logarithmic plot of parameter [B as a function of incision length.

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16 42 Zheng et al Z>.6 A- ~~~~~~ X-.4- Gg / -A- 3Sup 4 > Sup -o- ECCE Weeks Post-Op FIGURE 8 Recovery of visual acuity as a function of time after 3 incisions in superior meridian. was indistinguishable after 3-mm superior and temporal incisions, only the visual recovery after one 3-mm incision is plotted. ECCE Using the 36-month data as the reference point, maximum corrected acuity was reached between 4 and 6 weeks after surgery (Table VII). The acuity at 36 months differs from that at 4 weeks but not at 6 weeks. 6Sup Using the 3-month data as the reference point, maximum corrected acuity was reached between 1 and 2 weeks after surgery (Table VII). The 3- month acuity differs from that at 1 week but not that at 2 weeks. 3Sup Using the 18-month data as the reference point, best corrected acuity is reached between 1 day and 1 week after surgery (Table VII). The 18- month acuity differs from that at 1 day but not that at 1 week. 3Temp Using the 12-month data as the reference point, best corrected acuity is reached between 1 day and 1 week after surgery (Table VII). The 12- month acuity differs from that at 1 day but not that at 1 week.

17 Astigmatism After Phakoemulsification 43 AXIAL LENGTH AND INDUCED ASTIGMATISM To have sufficient numbers of cases, induced astigmatism was sampled between 6 and 24 months after surgery when the wounds were stable. Axial length did not affect the final change in astigmatism after ECCE or 6- and 3-mm superior scleral tunnel incisions (Table VIII). REFRACTION Manifest refractions were tabulated at least 6 months after surgery. The spherical equivalent of the ECCE group is significantly different than the smaller incisions, all of which are statistically indistinguishable (Table IX). The mean refractive sphere and cylinder of the ECCE cases also differ significantly from the small-incision groups, and the range of postoperative refractions is tighter and more predictable with the smaller incisions. The mean refractive sphere and cylinder of the 3Sup cases are significantly less than the two other small-incision groups, although the absolute differences are small. YAG LASER CAPSULOTOMY The cumulative incidence of laser capsulotomy is greater after ECCE than after phakoemulsification (Table X). Of the phakoemulsification groups, the 6Sup group has the longest follow-up, and the cumulative incidence of laser capsulotomy in this group is lower during the first 4 years after surgery. Compared with ECCE, the cumulative rate of capsulotomy also is lower during the first 2 years after 3Sup and the first year after 3Temp. DISCUSSION Many clinicians have documented their experience with various cataract surgical techniques, with and without sutures,'39 and several methods of calculating astigmatic change have been developed.4'11-4 Differences in surgical technique and analysis of induced astigmatism make it difficult to compare reports, but it is generally recognized that smaller incisions are better than larger incisions. The quantification of astigmatic change may give the impression of a greater degree of precision than is justified. Serial keratometric measurement of the axis and diopters of astigmatism of a normal cornea vary. Computerized topography may improve the accuracy and reproducibility of such measurements but does not eliminate error. Despite these limitations, a consistent method of comparison of cataract surgical incisions confirms the clinical impression that smaller is better. Detailed analysis of the induced change in postoperative corneal astigmatism shows conclusively that both the initial and final changes in corneal cylinder are less with 6- or 3-mm incisions for phakoemulsification than with ECCE. It has been suggested that corneal astigmatism may

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20 46 Zheng et al change gradually for years after the large incision for ECCE.7313' If this is true, some change in corneal astigmatism might be anticipated after an incision of any length, although it may be too subtle to detect with current technology. Statistical analysis of the data presented here indicates that the ECCE wound is astigmatically stable by 5 or 6 months after surgery and the 6-mm incision stabilizes by about 3 months after surgery, but inspection of the data for both the ECCE and 6Sup incisions suggests that a further ATR drift may occur after these times. It is possible that such ATR drift does occur in a subset of patients that is too small to detect in this series. To determine if longer eyes develop more astigmatism after surgery, eyes in the ECCE and 6Sup groups were subdivided on the basis of axial length. No relationship between axial length and induced astigmatism was detected, although the number of eyes with axial lengths over 25 mm was small. Using manifest refraction rather than keratometry to measure cylinder, Richards and colleagues7 also found no relationship between axial length and postoperative astigmatism after ECCE. These results suggest that the biology of wound healing is the same across the common range of human refraction. The genetic or environmental factors that regulate growth of the posterior segment in youth either do not influence cataract wound healing or are no longer active. Some investigators2'4'5 have suggested that final postoperative astigmatism and refraction can be influenced by choice of suture material. Proper alignment and closure of the wound certainly are important to minimize postoperative complications, especially with large wounds. The effect of sutures is more evident with large wounds; and if rapidly absorbable sutures are used, early wound gape and ATR astigmatism may develop.4 However, nonabsorbable sutures are the norm now for ECCE. After cutting tight sutures, Parker and Clorfeine' found that the number of remaining 1- nylon sutures did not affect long-term astigmatism. Drews3" cut no sutures and after 5 years found no difference in astigmatism in wounds closed with 1- nylon or 11- mersilene. Although the effect of sutures is less obvious after small incisions, in the first few months after phakoemulsification, suture technique may affect comeal astigmatism.' Studies with a longer perspective have not shown any consistent effect of sutures on comeal astigmatism."9"2-5 Assuming careful technique, we are skeptical of the surgeon's ability to reliably affect long-term postoperative astigmatism after a superior incision except with incision length. The evolution of less WTR astigmatism and more ATR astigmatism after superior incisions has been documented and is both normal and inevitable.'39'41 Prior to the development of phakoemulsification and IOLs, Troutman' suggested using a temporal ECCE incision to avoid excess ATR astigma-

21 Astigmatism After Phakoemulsification 47 tism, which might make contact lens fitting difficult. Clinical reports from Japan indicate that incisions on the superotemporal meridian induce less astigmatic change than those on the superior meridian.2 '629 This study has confirmed that even very small incisions induce less astigmatic change on the temporal meridian than the superior meridian. 14,33,36,37,39 Whether this effect is due to a fundamental difference in wound healing or to gravity is not known. The model presented in Eq(1) was developed to describe the change in induced corneal astigmatism after ECCE. The course of postoperative astigmatism is sufficiently uniform that by varying the parameters a and,b, the same model describes the astigmatic effect over time of any incision in the superior meridian. The curves of Figure 4 are derived from many data points, but the graphs relating the initial and final plateaus of induced astigmatism (Fig 6) and the values of the parameters a and a (Fig 7) to incision length are derived from only three incisions. With other lengths, the accuracy of these figures might improve, although they appear to be a reasonable way to estimate postoperative astigmatism. At least three data sets were thought necessary to test the general validity of the model, but the most recent data seem to make the model largely of historic interest. Small incisions have so little effect that induced astigmatic change is not a concern, and the model does not apply at all to incisions on the temporal meridian. Less astigmatism is not the only reason that patients see better sooner after careful phakoemulsification than after careful ECCE: The larger incision and expression of the nucleus generally cause more corneal edema. Placement of the IOL in an intact capsule improves the accuracy of the postoperative refraction, and with rapid stabilization of the wound, the surgeon may prescribe spectacles soon after surgery, if any are needed. In this series, the rate of capsulotomy was lower after small-incision surgery than after ECCE (Table X). Capsulorrhexis and placement of the IOL in an intact capsule are routine with phakoemulsification. Expression of the nucleus is difficult with an intact capsulorrhexis, and large IOLs with long haptics do not fit easily into an intact capsule. One or more radial tears in the anterior capsule are common with the "can opener" or scissors capsulotomy techniques used routinely for ECCE.4 With radial tears, one or both haptics of the IOL rest in the sulcus, and the anterior capsule adheres directly to the posterior capsule. Fibrosis of the capsule may be more rapid when the anterior and posterior capsule are broadly adherent. An intact anterior capsule also facilitates thorough removal of residual cortex and permits removal of some of the epithelial cells on the undersurface of the anterior capsule. Good results are the rule after intracapsular and extracapsular cataract

22 48 Zheng et al surgery. Even better results are the rule after less invasive small-incision surgery. The accuracy of the postoperative refraction is improved; the eye is quieter; and patients see better sooner. For those who have had experience with large and small incision techniques, the data shown in the tables and figures do not seem adequate to express the enthusiasm of both patients and physicians for the recent progress in cataract surgery. REFERENCES 1. Troutman RC. Control of corneal astigmatism in cataract and corneal surgery. Trans Pacific Coast Otolaryngol Ophthalmol Soc 197; 51: Stainer GA, Binder PS, Parker WT, et al. The natural and modified course of postcataract astigmatism. Ophthalmic Surg 1982; 13: Girard LJ, Rodriguez J, Mailman ML. Reducing surgically induced astigmatism by using a scleral tunnel. Am J Ophthalmol 1984; 97: Gorn RA. Surgically induced corneal astigmatism and its spontaneous regression. Ophthalmic Surg 1985; 16: Wishart MS, Wishart PK, Gregor ZJ. Corneal astigmatism following cataract extraction. BrJ Ophthalmol 1986; 7: Jampel HD, Thompson JR, Baker CC, et al. A computerized analysis of astigmatism after cataract surgery. Ophthalmic Surg 1986; 17: Richards SC, Brodstein RS, Richards WL, et al. Long-term course of surgically induced astigmatism. J Cataract Refract Surg 1988; 14: Parker WT, Clorfeine GS. Long-term evolution of astigmatism following planned extracapsular cataract extraction. Arch Ophthalmol 1989; 17: Shepherd JR. Induced astigmatism in small incision cataract surgery. J Cataract Refract Surg 1989; 15: Steinert RF, Brint SF, White SM, et al. Astigmatism after small incision cataract surgery. Ophthalmology 1991; 98: Samuelson SW, Koch DD, Kuglen CC. Determination of maximal incision length for true small-incision surgery. Ophthalmic Surg 1991; 22: Brint SF, Ostrick DM, Bryan JE. Keratometric cylinder and visual performance following phacoemulsification and implantation with silicone small-incision or poly(methyl methacrylate) intraocular lenses. J Cataract Refract Surg 1991; 17: Talamo JH, Stark WJ, Gottsch JD, et al. Natural history of corneal astigmatism after cataract surgery. J Cataract Refract Surg 1991; 17: Cravy TV. Routine use of lateral approach to cataract extraction to achieve rapid and sustained stabilization of postoperative astigmatism. J Cataract Refract Surg 1991; 17: Kondrot EC. Keratometric cylinder and visual recovery following phacoemulsification and intraocular lens implantation using a self-sealing cataract incision. J Cataract Refract Surg 1991; 17(suppl): Martin RG, Sanders DR, Van Der Karr MA, et al. Effect of small incision intraocular lens surgery on postoperative inflammation and astigmatism. J Cataract Refract Surg 1992; 18: Werblin TP. Astigmatism after cataract extraction: 6-year follow up of 6.5 and 12 millimeter incisions. Refract Corneal Surg 1992; 8: Dam-Johansen M, Olsen T. Refractive results after phacoemulsification and ECCE. Acta Ophthalmol 1993; 71: Gimbel HV, Sun R. Postoperative astigmatism following phacoemulsification with

23 Astigmatism After Phakoemulsifcation 49 sutured vs unsutured wounds. Can J Ophthalmol 1993; 28: Davison JA. Keratometric comparison of 4. and 5.5 mm scleral tunnel cataract incisions. J Cataract Refract Surg 1993; 19: Kawano K. Modified corneoscleral incision to reduce postoperative astigmatism after 6 mm diameter intraocular lens implantation. J Cataract Refract Surg 1993; 19: Masket S. One year postoperative astigmatic comparison of sutured and unsutured 4. mm scleral pocket incisions. J Cataract Refract Surg 1993; 19: El-Maghraby A, Anwar M, El-Sayyad F, et al. Effect of incision size on early post-operative visual rehabilitation after cataract surgery and intraocular lens implantation. J Cataract Refract Surg 1993; 19: Lemagne JM, Kallay. Astigmatism after a large scleral pocket incision in extracapsular cataract extraction. J Cataract Refract Surg 1993; 19: Oshika T, Tsuboi S, Yaguchi S, et al. Comparative study of intraocular lens implantation through 3.2- and 5.5-mm incisions. Ophthalmology 1994; 11: Hayashi K, Nakao F, Hayashi F. Corneal topographic analysis of superolateral incision cataract surgery. J Cataract Refract Surg 1994; 2: Sinskey RM, Stoppel JO. Induced astigmatism in a 6. mm no-stitch frown incision. J Cataract Refract Surg 1994; 2: Storr-Paulsen A, Vangsted P, Perriard A. Long-term natural and modified course of surgically induced astigmatism after extracapsular cataract extraction. Acta Ophthalmol 1994; 72: Hayashi K, Hayashi H, Nakao F, et al. The correlation between incision size and corneal shape changes in sutureless cataract surgery. Ophthamology 1995; 12: Gimbel HV, Sun R, DeBroff B. Effects of wound architecture and suture technique on postoperative astigmatism. Ophthalmic Surg Lasers 1995; 26: Drews RC. Astigmatism after cataract surgery: Nylon versus mersilene. J Cataract Refract Surg 1995; 21: Nielsen PJ. Prospective evaluation of surgically induced astigmatism and astigmatic keratotomy effects of various self-sealing small incision. J Cataract Refract Surg 1995; 21: Kohnen T, Dick B, Jacobi KW. Comparison of the induced astigmatism after temporal clear comeal tunnel incisions of different sizes. J Cataract Refract Surg 1995; 21: Storr-Paulsen A, Henning V. Long-term astigmatic changes after phaocemulsification with single-stitch horizontal suture closure. J Cataract Refract Surg 1995; 21: Oshika T, Tsuboi S. Astigmatic and refractive stabilization after cataract surgery. Ophthalmic Surg 1995; 26: Gross RH, Miller KM. Corneal astigmatism after phacoemulsification and lens implantation through unsutured scleral and corneal tunnel incisions. Am J Ophthalmol 1996; 121: Long DA, Monica ML. A prospective evaluation of corneal curvature changes with 3.- to 3.5-mm corneal tunnel phacoemulsification. Ophthalmology 1996; 13: M{iller-Jensen K, Barlinn B, Zimmerman H. Astigmatism reduction: No-stitch 4. mm versus 12. mm clear comeal incisions. J Cataract Refract Surg 1996; 22: Masket S, Tennen DG. Astigmatic stabilization of 3. mm temporal clear corneal cataract incisions. J Cataract Refract Surg 1996; 22: Cravy TV. Calculation of the change in corneal astigmatism following cataract extraction. Ophthalmic Surg 1979; 1: Merriam JC, Wahlig JB, Konrad H, et al. Extracapsular cataract extraction and posterior-lip sclerectomy with viscoelastic. Ophthalmic Surg 1994; 25: Jaffe NS, Clayman HN. The pathophysiology of corneal astigmatism after cataract

24 41 Zheng et al surgery. Trans Am Acad Ophthalmol Otolaryngol 1975; 79: Naeser K. Conversion of keratometer readings to polar values. J Cataract Refract Surg 199; 16: Holladay JT, Cravy TV, Koch DD. Calculating the surgically induced refractive change following ocular surgery. J Cataract Refract Surg 1992; 18: Assia EI, Legler UFC, Merrill C, et al. Clinicopathologic study of the effect of radial tears and loop fixation on intraocular lens decentration. Ophthalmol 1993; 1: DISCUSSION ROBERT C. DREWS, MD. Mathematical and optical concepts have always been challenging for ophthalmologists. Astigmatism is one of these. In the past 15 years, ophthalmology has advanced from taking on the burden of prescribing toric lenses, to making practical application of the overwhelming astigmatic data of corneal topography. Until 25 years ago, diopters of against-the-rule astigmatism was the expected and mostly accepted by-product of both classic extracapsular and intracapsular cataract surgery. The demand for optical perfection imposed by intraocular lenses required vastly improved control of wound closure. Silk and absorbable sutures allowed wound slippage even with microsurgery, and these were replaced by fine nylon, Prolene, and Mersilene. But even nonbiodegradable sutures have failed to eliminate late astigmatic shifts, and there has been a continued push toward the only alternative, smaller and smaller wound sizes. We have three questions before us. 1. Why the fundamental inability to eliminate late astigmatic shift from long wounds, no matter what wound architecture or how many sutures are used? Some data suggest continued wound remodeling even after 5 years. Is longitudinal shortening of the scar a factor? 2. How much does a smaller wound reduce astigmatism? 3. What are the effects of wound architecture and position? In this paper, Drs Zheng, Merriam, and Zaider attempt to give us longterm postoperative data relating astigmatic shift to wound size and position. Short-term studies of astigmatism assume "final" results incorrectly. There are two problems with long-term studies. Becaue a high percentage of patients are lost to follow-up, the data are less reliable. And, as Dr Merriam notes in this paper, sometimes the answers we eventually derive are no longer relevant or only "of historical interest" by the time a long-term study has been completed. This paper suffers the necessary faults of long-term, retrospective, nonrandom studies, with exclusion of many patients and absence of data on the majority of included patients on all visits. There were no data on the last visits for at least two thirds of the patients in each series. The last, "benchmark" visit varied from 8.5 years for ECCE to 1 year for 3 Temp.

25 Astigmatism After Phakoemulsification 411 The values of astigmatism used to calculate changes are softened by simplification of the axes. Conclusions must be drawn carefully and tentatively. We need random, prospective studies to answer our questions, with complete data and vector analysis, using the methods of Jaffe and Clayman or of Cravy, who is cited by the authors. While the formulas may daunt the average clinician, vector analysis solutions are easily programmed into spreadsheets. The exponential formula used for curve fitting in this paper justifies the use of a mathematician as a coauthor. While the mathematician in me finds the exponential curves beautiful, the practical clinician notes that the exercise may be unnecessary. Fitting an exponential curve to incomplete and approximate data may indeed imply "a greater degree of precision than is justified." Using a semi-log plot is a convenient way to compress long-term data onto a graph, but it exaggerates the first postoperative week, and the exponential curve fitted implies wound stability for the first week or so without data to support this assumption. Fortunately, the complexity of the mathematics fails to obfuscate the import of the authors' conclusions. The concept of astigmatic shift avoidance by minimizing wound size has proved useful: First, to argue the merits of small-incision surgery, to ballyhoo the superiority of those who master it, and to sell more expensive equipment, but, importantly, eventually to provide a quantum improvement in optical results and visual rehabilitation for all our patients. I read Dr Merriam's thesis in our Transactions with great interest. I deem it an honor to have been asked to discuss this paper, and a privilege to be the first to welcome the author to full membership in the American Ophthalmologic Society. DR VERINDER NIRANKARI. I have a couple of questions for Dr Merriam that are not clear to me from his paper. While we certainly accept the fact that shorter incisions do produce less astigmatism and more stable wounds, the question that Dr Merriam has not made clear in his presentation is whether the temporal incisions that were used were clear comeal incisions or also had scleral tunnel incisions as in the superior wounds. Also not mentioned is whether or not all the incisions were sutureless or with sutures and whether the sutures were horizontal or vertical sutures as we do know that vertical suturing can produce more astigmatism. The other question that is not answered is whether or not sutures were removed at any time after surgery, as that can again have a significant impact on post-operative astigmatism. Also, most of the foldable lenses that are used require a 3.8 to 4 mm incision rather than a 3 mm incision and it is not clear whether or not this had any impact on the final astigmatism. Finally, he reports that induced astigmatism was less with temporal

26 412 Zheng et al incision rather than superior incisions even though the exact reason for that is not stated in his paper. Again, I would like to thank Dr Merriam for this most excellent presentation. DR. R. TROUTMAN. As it is a subject in which I have had a long and abiding interest I would like to take this occasion to review some of the earlier attempts at control of astigmatism induced by the cataract incision. One of our members and my mentor, Dr John Mclean, was among the first to advocate direct suture of the cataract wound following intracapsular extraction. Although his technique was devised primarily to control other pathologies resulting from the unsutured cataract wound, it also served to minimize the astigmatism. Likewise, Kelman originally proposed a return to extracapsular extraction, done through a small incision by phacoemulsification, as a means to avoid the complications of the larger incision required for intracapsular extraction. It was not until a decade later that Shearing successfully secured an intraocular lens in the capsular bag after phacoemulsification. Today, the reduction in astigmatism as a result of the increasingly smaller incisions necessary for cataract extraction and lens implantation is recognized to be of great value to the final refractive result. My own interest in controlling astigmatism from cataract surgery began in 196 during the preparation of my thesis on intraocular lenses for admission to this society. At that time we used microsurgical techniques and closely place 8- silk sutures to limit the vision compromising astigmatism as well as other wound induced complications from the large cataract incision. In 1962 Harms and Mackensen introduced me to 1- monofilament nylon suture which provided much improved wound control and further reduced but did not eliminate astigmatism. In 1972 Jacques Charleux of Lyon, France convinced me to convert from a limbal to a corneal cataract incision which I have since used routinely for both large and smaller cataract incisions. When larger corneal incisions are closed with very deep or through and through sutures, not only is less astigmatism induced but also the cornea stabilizes quickly when the sutures are removed. In small corneal incisions no suture is necessary. As Dr Drews pointed out, with the typical limbal cataract incision there is a progressive corneal drift with flattening of the vertical meridian of the cornea, more or less "against the rule," depending on the age of the patient. This astigmatic shift is accentuated when the sutures are placed too superficially. The control of astigmatism resulting from the cataract incision has come a long way in the last 5 years. I would like to congratulate Dr Merriam for providing us with an excellent analysis of his own experience with some of the more recent techniques in cataract

27 Astigmatism After Phakoemulsification 413 wound closure. Hopefully, as far as astigmatism induced by the healing cataract incision is concerned, we are now only "flogging a dead horse." GEORGE L. SPAETH, MD. Two questions for Dr Merriam: Since the follow up for the groups with the temporal incisions were considerably shorter than for the group with the superior incisions, is it fair to consider the "long-term astigmatism" of these two groups in the same way? Second, why do you believe it is that performing cataract extraction with a temporal incision appears to be associated with less astigmatism than when the incision is performed superiorly, when the length of the incision temporally and superiorly is the same? ALEX IRVINE, MD. My question to John is much the same as the last speaker's. Why a temporal incision would not be expected to cause astigmatism? I wondered whether possibly your method of calculating astigmatic shift could play a role by taking only the 9 and 18 degree axes. I wonder whether your temporal incisions really centered on 3 o'clock or 9 o'clock position? I notice that with our cataract surgeons, very often their temporal incision tends to be at 1:3 or 2: o'clock with then a lower stab incision at 4:3 or 5: for the second instrument. If that were the case, would that throw off your calculations? In other words, if the incision is made at an oblique angle and you are only measuring your astigmatism at the two major axes, would that account for an apparent decrease in astigmatism? GEORGE STERN, MD. Dr Merriam says there is an induced plus cylinder in the direction of the incision. What he is basically saying is that the cornea is steepened in that area. You cannot steepen the cornea by making an incision. The best you can hope for is for it to heal exactly as it was before, which never happens. The incision weakens with a relaxing effect; and that is why you end up with plus cylinder at 18 degrees. Now, the only way that you can steepen the cornea is by placing a suture, so the degradation we see here is really an effect of the sutures loosening. This occurs first because of a decrease in wound swelling, and later from degradation or removal of the suture. Yet, we really didn't hear anything about what the practices were related to suture removel in these cases, whether there was significant variation, or whether there was an effort to leave all the sutures in place. We also didn't hear about variations in the use of steroids which would perhaps alter the timing of suture removal, or where the use of steroids would cause a weakening of the wound leading to more drift in those cases where steroids were used longer or sutures were removed earlier. I think this is an important consideration that we need to hear about from Dr Merriam. I do appreciate his presenting a very nice paper with an excellent analysis.

28 414 Zheng et al J.C. MERRIAM, MD. Thank you all for your comments, and I would like to thank Dr Drews in particular for his very thoughtful analysis. He made a number of points. One is that many of the patients were lost to follow-up. It seems to me that attrition is inevitable when one is following patients in their 8th decade of life. This does, of course, affect the numbers at each ofthe data points. Each ofthe data points on the astigmatism curves, however, represents a substantial number of patients, generally at least 3. We were concerned that perhaps this was too small a number for meaningful results, so we looked at the data after simply cutting in half. And, in fact, the curves are the same, although the standard deviation changes a bit. He also mentioned this is simple form of vector analysis. As stated in the paper, we used a simple case of Cravy's technique of vector analysis. Dr Drews wondered why we assumed axes of 9 and 18, rather than using the precise axes. There are two reasons for that. First, there is a fair amount of variability with serial keratometry. If you do keratometry on your secretary several times over the course of the day, I think you will find that not only the K value changes but the axis changes a little bit as well. There is an inherent error in the measurement of keratometry. But, does it make a difference? If you do vector analysis of, say, K values at 1 and 1, the numbers are very close to those when the axes are at 9 and 18. The inherent error of keratometry is probably greater than the error introduced by assuming that axes within 1 of 9 or 18 are 9 and 18. Also, the relative results also would not change as the convention for vector analysis was consistent for all surgical groups. Dr Drews also wondered what happened to the extracap group during the first week after surgery. Unfortunately after extracapsular surgery the corneas are too irregular for good K values, and so the extracap data begins at 2 weeks. It's only after phaco that you get accurate K's on the first postoperative day. So, just to reiterate, the consistent application of this convention gives relative results. The values of induced astigmatic change would be different with a different technique of vector analysis, although the relative results would be similar. Dr Nirankari asked whether a scleral or corneal incision was used. As shown on the slide, we used a 3 mm scleral tunnel. I have now moved more anteriorly into the cornea, so even the most recent data set is a little bit out of date. He asked whether a suture on the smaller wounds was used. In some cases yes and in some cases no. We looked at the data to see if a single suture had any effect on astigmatism, and it did not. Therefore, we simply lumped all of the data together. He also wondered how we were able to get an implant through a 3 mm wound. The lol:s were all silicone, and they pass through a 3 mm wound. I certainly enjoyed Dr Troutman's historical review. One of his papers is cited in the references, and we appreciate his long interest in astigmatism.