International Ophthalmology 16: 177-183, 1992. 9 1992KluwerAcademic Publishers. Printedin the Netherlands.

Astigmatism following cataract surgery: comparison of a scleral and a corneal incision in a mixed group of patients with and without glaucoma T.S. Lim, F.P. Gunning* & E.L. Greve Glaucoma Center, Academic Medical Center (AMC), University of Amsterdam, Meibergdreef 9, 1105 A Z Amsterdam, The Netherlands (* corresponding author) Accepted 17 April 1992

Key words: cataract, glaucoma, astigmatism, corneal incision Abstract We retrospectively analysed the course of postoperative corneal astigmatism and corrected visual acuity after extracapsular cataract extraction and posterior chamber lens implantation with either a corneal or a scleral incision in 170 eyes of 155 patients with and without glaucoma. A continuous 10/0 nylon shoelace suture was used for wound closure in two groups. In a third group, corneal wound closure was performed with a shorter shoelace suture in combination with two vicryl wing sutures at 11 and 1 o'clock. Although early postoperative mean astigmatism in eyes operated through a corneal incision was high (range 2.92-6.67 diopters at 1 month postoperatively) and significantly different when compared to eyes operated through a scleral incision (1.96 diopters), final mean astigmatism did not differ significantly between those two groups. Moreover, in 27% of eyes operated through a corneal incision, mean astigmatism at 2 months postoperatively was not significantly different from the scleral group and suture removal was not necessary. There was no statistically significant difference in corrected visual acuity over the entire study period between groups. Since safety and functional results of the corneal incision were not different from the scleral incision, we prefer a corneal incision in cataract surgery because of its surgical advantages, especially in patients with cataract and coexisting glaucoma.

Introduction The amount of postcataract astigmatism is related to a variety of factors such as technique of incision [1-3] and suturing [4-6], the use of an operative keratometer [7-9] and the location of incision [2, 4, 10-12]. From these studies it appeared that although more anteriorly situated incisions initially cause more (suture-induced) astigmatism, final (surgically induced) astigmatism may not be significantly greater [13]. Important postoperative variables of postoperative astigmatism are the use of topical

corticosteroids and premature suture removal. The preoperative astigmatic error should also be considered. Occasionally, non-corneal astigmatism is caused by a tilted or optically imperfect intraocular lens [13]. The main cause of postoperative with-the-rule astigmatism is wound compression due to the sutures. Wound gape, premature absorption of absorbable sutures, or early removal of non-absorbable sutures may induce against-the-rule astigmatism. Wound misalignment may cause astigmatism located in any axis. Advantages of a corneal incision are preserva-

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tion of the conjunctiva for future filtering surgery in patients with coexcisting glaucoma, reduction of operation duration, and less frequent bleeding and iris incarceration due to the anteriorly situated position of the corneal incision. Moreover, in eyes with prior successfull filtering surgery the filtration site is avoided and the chance on postoperative bleb failure is minimized. One report showed a lower rate of postoperative intraocular pressure elevation after the use of a corneal incision when compared to a limbal incision [14]. The authors suggested that a limbal incision caused more trabecular damage, thereby reducing aqueous outflow. Disadvantages of a corneal incision are a delay in visual rehabilitation, a higher risk for damage to the corneal endothelium, and delayed wound healing with the possibility of subsequent wound dehiscence. In addition, postoperative patientcare is often more laborious because of the necessity for suture cutting and removal. The aim of this study was to analyse the magnitude and duration of the changes in corneal curvature using different techniques of incision and suturing in cataract surgery of a mixed group of patients with and without glaucoma. In addition, we compared the safety and functional results of the corneal incision versus a scleral incision.

Patients and methods

The study included 170 eyes of 155 patients which had undergone extra- or intercapsular cataract extraction and posterior chamber intraocular lens (ECCE + PC-IOL) implantation by one of the authors (ELG). The follow-up period was more than one year for all patients. Postoperative keratometry readings were collected at week 1 (wk 1), 1 month (Mth 1), 2 months (Mths 2), 5 months (Mths 5), 1 year (ly) and 18 months (> 1 y). Two different incisions were used: one group of eyes (n-- 119) was operated through a corneal incision and another group (n = 51) consisted of eyes in which a (corneo)scleral incision was performed. All incisions were closed by a 10/0 nylon continuous shoelace suture. The corneal incision

group was divided into two sub-groups in which the corneal incision was closed by either a continuous shoelace suture (n = 70) or a shoelace suture in combination with two vicryl sutures at each end of the incision (n = 49). The groups were comparable in terms of followup, average age, follow-up period, and gender distribution. The three groups will be described in details. 1. The scleral (S) group consisted of 51 eyes in which a sharp bevelled 13 mm (corneo)scleral incision, from 10 to 2 o'clock, was performed to open the anterior chamber. The incision was closed with a continuous 10/0 nylon shoelace type suture. In 48 eyes, ECCE was followed by implantation of a modified Sinskey type J-loop IOL in the ciliary sulcus. In 3 eyes an iris clip lens was implanted. Glaucoma was present in 42% of the cases. 2. The corneal/nylon (CN) group consisted of 70 eyes in which a bevelled 10 mm corneal incision, just anterior to the limbus was performed. The incision was closed with a continuous 10/0 nylon shoelace suture. In 61 eyes a rigid Galand disc IOL was implanted in the capsular bag and in 9 eyes a modified Sinskey J-loop IOL was fixated in the ciliary sulcus. Preexistent glaucoma was present in 50% of the patients. 3. The corneal/nylon-vicryl (CNV) group consisted of 49 eyes. In this group the same incision was made as in the former group, but wound closure was performed with a shorter continuous shoelace suture in combination with two vicryl wing sutures at 11 and 1 o'clock. This modification was thought to reduce oblique astigmatism. In 22 eyes ECCE was followed by implantation of a 9.0 mm rigid Galand disc IOL and in 27 eyes an 8.5 mm disc IOL was implanted in the capsular bag. Preexisting glaucoma was found in 24.5% of the patients. Sutures were left in situ in the eyes with a scleral wound. In the eyes with a corneal incision, the nylon sutures were removed when the degree of astigmatism exceeded two diopters two months af-

Astigmatism following cataract surgery ter tapering the administration of topical steroids. The sutures were first cut with an Argon laser and subsequently removed with a forceps. Preoperative and postoperative keratometry readings were used for calculation of the astigmatism values at different times. Surgically induced astigmatism was calculated using the law of sines and cosines, as described by Jaffe and Clayman [15]. A t-test was used for statistical analysis. A p-value of less than 0.05 was considered statistically significant.

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110.4 degrees in the CN group without ROS. In the CNV group this was 1.09 diopters at 84 degrees when the sutures were removed, and 1.66 diopters at 109.6 degrees when the sutures were left in situ. Sutures were removed in 70% of cases in the CN group and in 78% of eyes in the CNV group. There were no significant differences in mean postoperative astigmatism between patients with and without glaucoma.

Axis of astigmatism Results

Degree of astigmatism (Table 1) Figure 1 graphically depicts the data of mean degree (_+ SD) of astigmatism during the pre- and postoperative period. Early postoperative astigmatism in both corneal incision groups was significantly different from the scleral incision group. At one month postoperatively, mean astigmatism was 5.92 (_+ 1.91) diopters in the CN group and 6.67 (+ 1.80) diopters in the CNV group with removal of sutures (ROS). This compares to a mean astigmatism of 1.96 (_+ 1.06) diopters in the scleral incision group, 2.92 (+ 1.76) diopters in the CN group, and 4.02 diopters (_+ 2.13) in the corneal incisions groups, which did not need suture removal. In the eyes without ROS, astigmatism decreases gradually in the early postoperative period. At 2 months postoperatively, the astigmatism of the CN group and the CNV group was not longer significantly different from the scleral incision group. In the eyes which needed removal of sutures, a steep fall in power of astigmatism was found after 2 months. Mean astigmatism at 5 months postoperatively was 1.92 (_+ 1.52) diopters in the CN group, and 1.97 (_+ 1.76) diopters in the CNV group which was not significantly different when compared to the scleral group. After one year, surgically induced astigmatism was 1.52 diopters at 98.0 degrees in the scleral group, 1.42 diopters at 102.5 degrees in the CN group with removal of sutures, and 1.53 diopters at

The following definitions are commonly used to describe the corneal curvature: with-the-rule (WR) astigmatism is defined as when the steepest corneal meridian is between 90~ 30 ~ against-the-rule (AR) astigmatism is present when the steepest corneal curvature is between 180~ _+ 30 ~ the remaining 60 ~ representing oblique (OBL) astigmatism. The changes in axis of astigmatism occurring in each group over the postoperative period are shown in Figs 2, 3 and 4. An evident shift towards WR astigmatism was found in all groups in the early postoperative period. Final with-the-rule astigmatism was associated with the scleral incision and with a corneal incision when suture removal was not necessary. Againstthe-rule astigmatism was slightly more frequently found among the eyes in the CN group after ROS and in the majority of eyes in the CNV group after ROS. Spherical eyes (SPH) and oblique astigmatism were found in a small number of patients. There was no difference in oblique astigmatism between the two corneal incision groups. Comparing the preoperative number of eyes with WR, AR, and OBL astigmatism with postoperative findings, there is in the scleral group a shift to more eyes with WR and in a lesser degree to OBL astigmatism, where as in the corneal groups the loss of spherical eyes is more equally distributed among WR, AR and OBL astigmatism (Table 2).

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--~-

Scleral

>
ly

1 year

Fig. 1. M e a n astigmatism.

one year postoperatively (Fig. 5). Similar figures were found in the two corneal incision groups. After one year, 86% of all eyes had a best corrected visual acuity of 20/40 or better. Best case analysis showed no statistically significant difference in corrected visual acuity over the entire postoperative period between the three groups.

Visual acuity Preoperative corrected visual acuity was not significantly different between all groups (0.24-0.29). In the scleral group, mean corrected visual acuity was 0.49 in the first week, and improved to 0.74 after

Table 1. M e a n astigmatism (diopters _+ SD) during the study period. Time

Patient groups

Preop Wk 1 Mthl Mths 2 Mths 5 1 Year 18 Mths

1Scleral

zCN/ROS +

3C N / R O S -

4C N V / R O S +

5C N V / R O S -

0.81 + 2.36+ 1.96+ 1.55 + 1.28 + 1.23 _+ 1.24 +

0.83 _+ 7.10_+ 5.92_+ 4.74 _+ 1.92 + 1.53 + 1.37 _+

0.68 + 0.74 4.08_+ 2.03 2 . 9 2 + 1.76 2.05 _+ 1.28 1.78 _+ 1.05 1.53 _+ 0.72 1.35 + 0.70

0.64 + 6.95+ 6.67_+ 5.14 + 1.97_+ 1.15 _+ 1.09 _+

1.00+ 5.11_+ 4.02+_ 2.05 _+ 1.70_+ 1.46 _+ 1.45 _+

0.96 1.45 1.06 0.91 0.78 0.87 0.82

0.68 2.06 1.91 1.78 1.52 0.96 0.81

Patient groups. 1S c l e r a l 2CN / ROS + 3CN / ROS4CNV / ROS + 5CNV / ROS-

= = = = =

scleral incision group, corneal/nylon group with removal of sutures. corneal/nylon group without removal of sutures. corneal/nylon/vicryl group with removal of sutures. corneal/nylon/vicryl group without removal of sutures.

0.58 1.75 1.80 3.01 1.76 0.96 0.80

0.98 2.77 2.13 1.14 0.93 0.62 0.55

Astigmatism following cataract surgery

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dehiscention, iris incarceration, and hyphema were not found.

NO. Of eyes 35 30 25 20

i

15

"i

Discussion

10 5 0 preop,

wk 1

rnth 1

rnths 2

mths 5

1 year

time WR

~;~G AR

:' OBL

~

SPH

Fig. 2. Axis of astigmatism (scleral incision). No. of eyes

6O 5O 40 30 20 10 0 preop,

wk 1

mth 1

mths 2

mths 5

1 year

time m m WR

~

AR

~

OBL

~

SPH

Fig. 3. Axis of astigmatism (corneal/nylon incision). NO. of eyes

so ]1 40 30 20 10

1 preep.

wk 1

ruth 1

mths 2

! mths 5

1 year

time mllll WR

~

AR

~ l ~ OBL

'~--~ SPH

Fig. 4. Axis of astigmatism (corneal/nylon-vicryl incision).

Incision and~or suture-related complications Complications encountered included transient corneal decompensation, which was noted in one eye (2%) of the scleral incision group, and three eyes (2.6%) of the corneal incision group. Discomfort caused by the vicryl sutures urged for suture removal in 3 eyes. Neovascularization of the wound was sometimes noticed when sutures were causing irritation and not immediately removed. Wound

In contrast to a corneal incision, a scleral incision is likely to cause intraoperative bleeding with subsequent scarring in the limbal region. In case of a compromised conjunctival area due to prior scleral surgery, subsequent glaucoma surgery is prone to result in an increased number of cases with inflammatory complications, bleb failure, and hyphema. The safety and functional results of patients operated through a corneal incision are satisfactory. Final astigmatism and visual acuity compared equally to patients operated through a scleral incision. This is in keeping with earlier reports on corneal astigmatism [2]. It has been suggested that postoperative astigmatism after a corneal incision results in a slower visual rehabilitation. We have only measured corrected visual acuity, which showed no significant differences between the three groups. Suture removal may be regarded as a disadvantage of the corneal incision technique. However, in 27% of eyes operated through a corneal incision, suture removal was not necessary and mean astigmatism at 2 months postoperatively was not significantly different from the scleral group. In addition, corneal astigmatism decreased rapidly after cutting of the sutures and instantly approached the same level of astigmatism as was found in the other groups. There seems to be a tendency to against-the-rule astigmatism after removal of the sutures. The use of two vicryl wing sutures did not prevent the occurrence of postoperative oblique astigmatism. In addition, irritative symptoms were not infrequent. Postoperative best corrected visual acuity was comparable to other reports dealing with cataract surgery in a mixed population of patients with and without glaucoma [16]. There were no clinical signs of damage to the endothelium, neither did we find wound dehis-

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[]

o

scleral

•

C N/ R O S*

CNV/ROS+

x

CNV/ROS-

CN/ROS-

c o r r e c t e d visual a c u i t y

1

0.8 0.6 0.4 0.2 0 preop.

i

i

wk 1

mth 1

i

i

mths 2

mths 5

_

1 year

time

Fig. 5. Visual acuity.

cence among our patient material. However, the latter is certainly something to be cautious of, especially in patients in whom prolonged use of topical steroids is indicated. A detachment of Descemet's membrane was not noted in this study, although sometimes regarded as a serious risk of a corneal incision [17]. Only one case (0.5%) of stripped Descemet's was found in a larger serie of 197 eyes in which a similar surgical technique was used [16]. In patients with a functioning filtering bleb, special attention is needed with respect to the location of incision. A corneal section is probably the safest approach in these patients. One report suggested that the application of glaucoma drugs may alter wound healing in the

perilimbal region [18]. We were interested whether this phenomenon affected postoperative astigmatism. However, we found no significant difference in astigmatism between patients with and those without glaucoma. The preference of a corneal incision or a scleral incision in patients without glaucoma is often a matter of personal taste of the surgeon. However, in patients with coexisting glaucoma who need cataract surgery, a corneal incision is given the surgical advantages, safety, and functional results, the method of choice.

Table 2. Percentual distribution of astigmatism.

Scleral Corneal nylon Corneal vicryl

-

preop final preop final preop final

WR

AR

OBL

SPH

23.5% 37.3% 38.6% 42.9% 20.0% 24.5%

45.1% 43.1% 35.7% 42.9% 53.1% 57.2%

2.0% 9.8% 5.7% 11.4% 6.1% 12.2%

29.4% 9.8% 20.0% 2.8% 20.4% 6.1%

Astigmatism following cataract surgery Acknowledgement The authors acknowledge R. Nuyts, MD, for helping with revisions.

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