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J.E. Merriam, L. Zheng, J.C. Merriam, T. Sullivan, A. Kelly; Stabilization of the Axis of Corneal Astigmatism After Cataract Surgery . Invest. Ophthalmol. Vis. Sci. 2006;47(13):662.
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To compare the effect of length and location of incisions for cataract using a proportional hazard model to describe the change of the axis of corneal astigmatism after surgery and to compare the effect of different incisions on the probability of corneal stabilization after surgery.
This is a review of 6 incisions – 12 mm superior scleral incision (ECCE), 6 mm superior scleral incision (6Sup), 3 mm superior scleral incision (3Sup), 3 mm temporal scleral incision (3Temp), 3.5 mm temporal cornea incision (3.5Cor) and 2.6 mm temporal cornea incision (2.6Cor). The study was limited to the first 5 years after surgery. The review includes 1267 eyes of 937 patients: ECCE 165 eyes; 6Sup 93 eyes; 3Sup 143 eyes; 3Temp 95 eyes; 3.5Cor 449 eyes; and 2.6Cor 322 eyes. Corneal astigmatism, measured with a manual keratometer before and after surgery, was divided into 4 groups: vertical when the steeper axis ranged from 70° to 110°; horizontal when the steeper axis ranged from 0° to 20° or from 160° to 180°; and oblique when the major axis ranged from 20° to 70° or from 110° to 160°. The eye was considered spherical when corneal astigmatism was less than or equal to 0.75 D.
A proportional hazard model was fitted to assess the effect of each incision type on the time to stabilization of the axis of corneal astigmatism, adjusting for patient age and gender. Models were fitted initially for all data in each incision group. Each incision group was then subdivided into eyes with preoperative vertical, horizontal, and spherical corneal astigmatism, and separate models were fitted to these data sets. The analyses were done using SAS 9.1. The plots were generated from the model fits using R 2.2.0.
After a superior incision, the time to stabilization of the axis of corneal astigmatism decreased with incision size, and the probability of immediate stabilization increased with decreasing incision size. All temporal incisions stabilized more rapidly than the superior incisions. The probability of immediate stabilization did not differ significantly among 3Temp, 3.5Cor, and 2.6Cor. After a 3.5 mm corneal incision eyes with preoperative vertical astigmatism stabilized slightly more rapidly than eyes with preoperative horizontal astigmatism. The axis of preoperative corneal astigmatism did not appear to influence time to stabilization after a 2.6 mm corneal incision.
The time to corneal stabilization was significantly shorter for the more recent incision methods. This analysis did not show a significant difference in time to stabilization after any of the small temporal incisions.
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