Comparison of surgically induced astigmatism of temporal versus superior clear corneal incisions

Purpose
Comparison of the astigmatism induced by the operation based on the 2.8 mm incisions in the clear cornea, performed by temporal approach and superior approach.

Material and methods
Retrospective analysis was performed on the group of 65 patients (41 women and 24 men), mean age 74.5 ± 7.1 years old. We studied a series of 70 eyes (32 right eyes and 38 left eyes). All of the patients underwent cataract surgery by means of ultrasonic phacoemulsification conducted at the Department of Ophthalmology, Military Health Services Institute in Warsaw, Poland within 2004-2005. Follow-up examinations took place 6 months after operation. There were DBCVA. NBCVA, intraocular pressure, anterior segment of the eye and fundus examined. Curvature of the cornea was measured by means of Javal’s ophthalmometry. The results were assumed as significant in view of corneal curvature stabilization. Vector analysis of astigmatism was performed on the basis of method described by Jaffe. There was preoperative astigmatism vector (K1) and post-operative astigmatism vector (K3) calculated, as well as surgically inducted astigmatism (SIA) – vector (K2). From the group of 70 eyes, 19 were excluded from the study, where vector K1 was >1.0 D as well as four eyes, where the main opening site depended on the size and axis of K1 vector. The group of 47 eyes was divided according to the opening site into two subgroups- group I (temporal approach – 2.8 mm) – 25 eyes and group II (superior approach 2.8 mm) – 22 eyes. Statistical analysis was performed based on Statistica package 6.0 PL., using U-Mann-Whitney’s test, Chi square Yates’ test, Kruskal-Wailis’ variance analysis, logistic regression and W Shapiro-Wilk’s test.

Results
Studied groups were homogeneous with respect to age structure, sex, number of operated eyes and pre-operative size of corneal astigmatism vector K1 (p>.05). The mean values of SIA in group I and II were respectively: 0.63± 0.28 and 1.00 ± 0.54 and were statistically significant (p<.05). The mean values of K3 post-operative vector measured 6 months following the operation was: 0.54± 0.35 in the group I and 0.96 ± 0.43 in the group II. Differences between two groups show statistical significance (p<.05). Size of SIA has crucial influence on generating post-operative astigmatism >1.0 D (p=.03).

Conclusions
Clear corneal temporal approach 2.8 mm is more beneficial method comparing to superior approach of the same width, because of the scale of SIA.