Purpose
To compare long-term change in corneal astigmatism with advancing age between eyes that underwent sutureless cataract surgery and those that did not undergo surgery.
Design
Case-control study.
Methods
A total of 153 eyes that underwent phacoemulsification with a horizontal incision more than 11 years ago (surgery group) and 153 age-matched control eyes that did not undergo surgery (nonsurgery group) were enrolled. The keratometric cylinder at baseline (at 1 year or more postoperatively in the surgery group) and at 5 and 10 years after baseline was examined. The corneal astigmatic change, as calculated using polar value analysis and vector decomposition analysis, between baseline and 5 years after baseline and between 5 and 10 years was compared between the groups.
Results
The mean corneal astigmatic change, specifically ΔKP (90) in the polar analysis and against-the-rule component in the vector analysis, between baseline and 5 years and between 5 and 10 years showed an against-the-rule change in both groups. Using multivariate analysis, no significant difference was found in the corneal astigmatic change between the 2 groups at either time interval ( P ≥ .126). Furthermore, the change between baseline and 5 years was similar to that between 5 and 10 years in both groups ( P ≥ .315).
Conclusions
Corneal astigmatism after sutureless cataract surgery shows a long-term against-the-rule change with advancing age, and this change is similar to that of normal cornea, suggesting that the against-the-rule change that occurs subsequently should be taken into consideration at the time of cataract surgery.
Advances in surgical techniques and devices, including the toric intraocular lens (IOL), a limbal relaxing incision, or an opposite clear corneal incision, have enabled us to correct preoperative astigmatism during cataract surgery. On the other hand, it is well known that corneal astigmatism of healthy subjects generally changes from with-the-rule astigmatism to against-the-rule astigmatism with aging. Accordingly, surgeons should take into consideration how the corneal astigmatism may continue to change subsequent to stabilization of any surgically induced change when they correct astigmatism at the time of cataract surgery. For instance, it remains unclear as to whether or not a small amount of with-the-rule astigmatism in young and middle-aged patients should be fully corrected, since the astigmatism may shift to an against-the-rule orientation with passing time.
It has been shown that a surgically induced change in corneal astigmatism after unsutured cataract surgery shows an against-the-wound change. Accordingly, an against-the-rule shift occurs when the wound is made superiorly, while a with-the-rule shift occurs when the wound is made horizontally. A number of studies have shown that the surgically induced change in corneal astigmatism stabilizes within a year after surgery. In contrast, long-term studies described by Rainer and associates and by Drews showed that the against-the-rule astigmatic shift continued for up to 5 years after sutureless cataract surgery. However, since the incisions were made at the 12-o’clock meridian, it is unclear whether the against-the-rule shift shown in those studies was attributable to the surgery or to aging.
The purpose of the study described herein was to examine whether or not corneal astigmatism continues to change subsequent to stabilization of the surgically induced change resulting from sutureless cataract surgery. Furthermore, when corneal astigmatism continued to change, we attempted to investigate whether or not the long-term change in corneal astigmatism was different from the aging change of healthy corneas that did not undergo any surgery. To exclude the influence of surgically induced against-the-rule astigmatic shift, only eyes that underwent sutureless cataract surgery with a horizontal incision were enrolled in this study. In addition, to properly compare the vector change in corneal astigmatism shown in 2 variables, multivariate analysis was used for statistical comparison.
Methods
Patients
The medical records of all patients who had undergone sutureless cataract surgery with implantation of a foldable IOL at the Hayashi Eye Hospital between January 6, 1995 and June 30, 1999 were reviewed. Only those eyes that underwent a follow-up of 11 years or longer from the time of cataract surgery were enrolled (surgery group). Inclusion criteria for the surgery group were: 1) eyes that underwent at least 2 examinations by an autokeratometer at one year postoperatively or later, and in which the difference between the two examinations was within 0.5 diopters (D) in cylindrical power and within ± 15 degrees in cylindrical axis (the latter examination was defined as baseline); 2) eyes that underwent examinations by the autokeratometer at approximately 5 and 10 years after baseline; 3) eyes that underwent phacoemulsification surgery with an unsutured horizontal incision; 4) first-operated eye if the patient had undergone bilateral cataract surgery; 5) eyes that had uneventful surgery; 6) eyes with no comorbidity of the cornea, optic nerve, or macula; 7) eyes with no history of other surgery or inflammation; and 8) eyes without severe chronic eyelid disease during follow-up. Based on these criteria, 153 eyes were identified. The mean interval between baseline and the last visit before baseline was 3.4 ± 2.3 months, with a range of 0.4 to 9.6 months. For controls, 153 age-matched eyes, the patients being within 5 years of the same age as those in the surgery group, that did not undergo ocular surgery during a follow-up of 11 years or longer were enrolled (nonsurgery group). Inclusion criteria for the nonsurgery group were: 1) eyes that underwent examination by an autokeratometer at baseline, and at approximately 5 and 10 years after baseline; 2) eyes with no comorbidity of the cornea, optic nerve, or macula; 3) eyes with no history of other surgery or inflammation; and 4) eyes without severe chronic eyelid disease during follow-up. In the surgery group, 128 eyes received a hydrophobic acrylic IOL (MA60BM; Alcon Laboratories, Fort Worth, Texas, USA) through a 4.1-mm straight corneoscleral incision, and 25 received a silicone IOL (SI26NB, SI30NB, or SI40NB; Abbot Medical Optics [AMO], Santa Ana, California, USA) through a 3.0- or 3.5-mm corneoscleral or clear corneal incision.
Surgical Procedure
One surgeon (K.H.) performed all surgeries using almost the same surgical procedure as described previously. First, a continuous curvilinear capsulorrhexis measuring approximately 5.5 mm in diameter was accomplished using a 25-gauge bent needle through a side port. After continuous curvilinear capsulorrhexis, a corneoscleral or clear corneal incision was made at the 9-o’clock meridian (temporally in the right eye and nasally in the left eye) for phacoemulsification. The straight corneoscleral incision was made using a diamond knife (No. 41305; Huco, St-Blaise, Switzerland) and a diamond crescent knife (No. 41389; Huco) and a 2.5-mm stainless steel keratome (Inami, Tokyo, Japan), while a clear corneal stab incision was made using the 2.5-mm stainless keratome. After hydrodissection, endocapsular phacoemulsification of the nucleus and aspiration of the residual cortex were carried out. Using a short-cut stainless steel keratome (Alcon Laboratories), the wound was enlarged to 3.0, 3.5, or 4.1 mm for implantation of the IOL. The lens capsule was inflated with sodium hyaluronate 1% (Healon; AMO), after which an IOL was placed into the capsular bag using an IOL forceps (AE-4272; ASICO, Westmont, Illinois, USA). After IOL insertion, the viscoelastic material was thoroughly evacuated. No suture was placed and the wound was not hydrated in any of the cases.
Main Outcome Measures
Data on the eyes that underwent sutureless cataract surgery (surgery group) and on the control eyes that did not undergo surgery (nonsurgery group) were recorded. These data included corneal curvature at the steeper meridian and that at 90 degrees from the steeper meridian, as well as refractive spherical and cylindrical powers as measured using an autokeratometer (ARK-700A; NIDEK, Gamagori, Japan). The uncorrected and spectacle-corrected visual acuity measured on a decimal chart, time interval between surgery and examination, length and type of incision, and type of IOL implanted were also recorded.
The interval change in corneal astigmatism between baseline and 5 years after baseline and between 5 and 10 years after baseline was analyzed using the polar value method described by Naeser and Hjortdal and the vector decomposition method described by Holladay and associates. The surgically induced change in corneal astigmatism between the preoperative time point and baseline in the surgery group was also determined using the same two methods. The polar coordinate system was further converted to the vector coordinate system (change vector magnitude and meridian). The Naeser polar value method shows vertical change in corneal astigmatism as ΔKP (90) and torque as ΔKP (135). A positive ΔKP (90) indicates a steepening of the vertical meridian, which is a with-the-rule change, while a negative ΔKP (90) indicates a flattening of this meridian, which is an against-the-rule change. A positive ΔKP (135) indicates an anticlockwise torque, while a negative ΔKP (135) indicates a clockwise torque. The Holladay-Cravy-Koch method decomposes the change vectors to a with-the-rule component (180 degrees) and an against-the-rule component (90 degrees). A positive against-the-rule component indicates a flattening of the vertical meridian, which is an against-the-rule change, while a positive with-the-rule component indicates a flattening of the horizontal meridian, which represents a with-the-rule change.
Statistical Analysis
The normality of data distribution was tested using the Kolmogorov-Smirnov test. Since portions of the data regarding corneal astigmatism, change in corneal astigmatism, manifest spherical equivalent value, and some of the other variables did not show a normal distribution, nonparametric analyses were used in this study. Differences in the change in corneal astigmatism between the surgery and nonsurgery groups and between the 2 intervals (baseline to 5 years after baseline and 5 to 10 years after baseline) were compared using the Mann-Whitney U test and the spatial sign-based multivariate analysis of variance. Corneal astigmatism and the other continuous variables were compared between the two groups and between the time intervals using the Mann-Whitney U test. A difference in the number of eyes that showed a with-the-rule, against-the-rule, or oblique corneal astigmatism and the other discrete variables between the 2 groups and between the time intervals was compared using the χ 2 or Fisher exact probability test. Any differences showing a P value of less than .05 were considered to be statistically significant.
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