Clear corneal incision of 2.75 mm for cataract surgery induces little change of astigmatism in eyes with low preoperative corneal cylinder.

PURPOSE: To assess the early astigmatic effect induced by 2.75 mm clear cornea incisions with different locations for cataract surgery. METHODS: A total of 146 eyes of different patients were studied prospectively. Cataract surgery was performed by three surgeons, two using a temporal approach and one using a superior approach. For both approaches, the site of the 2.75 mm incision was allowed to vary slightly according to the characteristics of the eye and orbit. Computerized videokeratography was used to measure corneal astigmatism before surgery and after 1, 4, and 12 weeks. Corneal astigmatism was recorded as cylinder and axis and it was then converted to 2 power vector. Model based prediction and comparisons were made for the most commonly used corneal incision sites: 12 (both eyes), 2 (left eye), and 8 (right eye) o'clock meridian. RESULTS: After 3 months the differences in corneal astigmatism (JCC 0 ) between the incisions performed at 12 and 2 o'clock were not statistically significant (-0.08, 95% CI: -0.19, -0.02); the differences in JCC 0 between incisions at 12 and 8 o'clock were -0.17 (95% CI: -0.30, -0.05; p<0.01). After 3 months the change in JCC 0 for the patients with 0.5 D with-the-rule preoperatively were -0.32 (95% CI: -0.44, 0.21; p<0.01) for incisions at 12; -0.24 (95% CI: -0.36, 0.13; p<0.01) for incisions at 2; and -0.15 (95% CI: -0.27, -0.03; p<0.05) for incisions at 8. After 3 months the changes of JCC 0 for the patients with -0.5 D against-the-rule pre-operatively were 0.10 (95% CI: 0.04, 0.23) for incision at 12; 0.18 (95% CI: 0.04, 0.32; p<0.05) for incisions at 2; and 0.27 (95% CI: 0.14, 0.40; p<0.01) for incisions at 8 o'clock. The oblique astigmatic vector (JCC 45 ) was very modest in this sample before surgery and underwent minimal and nonsignificant change after it. CONCLUSIONS: This study has shown that a 2.75 mm clear corneal incision causes a small change of corneal cylinder regardless of incision site.