Surgically Induced Astigmatism After 2.75 mm Clear Corneal Incisions for Cataract Surgery

Abstract

Abstract: : Purpose: To determine early astigmatic effect induced by 2.75 mm clear cornea phacoemulsification cataract incisions Methods: Seventy eyes of different individuals were included. The corneal incision was applied at different clock–hours grouped in 3 categories: at 12 in 7 right eyes and 9 left eyes, at 7–9 in 34 right eyes and at 2–3 in 20 left eyes. Corneal curvature was obtained before surgery at 1 week and 1 month using computerized videokeratography (EyeSys Corneal Analysis System, EyeSys laboratories, Inc.) The difference in curvature between the two orthogonal meridians was registered as a cylinder with a given axis corresponding to the more curve meridian and assuming orthogonality of the meridians. This cylinder was transformed into a vector using a power vector transformation into 2 Jackson crossed–cylinders, on with 0°/90° axis (JCC0) and one with 45°/145° axis (JCC45) in order to compute the change of each component and of the total cylinder vector between baseline and 1 month. A paired t–test was used to compare the change of the JCC components and a Hotelling T test was used to assess the overall change of the cylinder vector. Regression analysis was used to assess factors influences the change of the cylinder components, including baseline cylinder and incision site. Results: There was no statistically significant change of the JCC0 after surgery, the mean of which changed by –0.01D (SD=0.35D, p=0.846), whereas there was a modest but significant mean change of the JCC45 by –0.09 (SD=0.33D, p= 0.020) for the JCC45. The overall change of the total cylinder vector showed only a trend towards significance (p=0.066) cylinder, with a median change of 0.27D and a change of less than 1D in 67/70 eyes (96%). There were no factors influencing the JCC45 shift when the baseline value was considered. On the contrary the change of the JCC0 vector was larger for the 12 o’ clock incision vs both lateral incisions with an interaction term with the baseline JCC0 suggesting a larger increase of negative baseline values by –1.4 D vs –0.6 D when the baseline JCC0 was –1D (p<0.001). Conclusions: Cataract surgery with a 2.75 mm incision leads to modest change of the corneal astigmatism after 1 month. A later incision at 8 o’clock in the right eye or at 2 o’clock in the left eye causes less increase of the counter–the–rule astigmatic component than a 12 o’clock incision in this setting.

Keywords: astigmatism • treatment outcomes of cataract surgery • topography