Comparison of Mean and Centroid of Surgically Induced Astigmatism After Standard Cataract Surgery

Purpose: To compare the arithmetic mean of surgically induced astigmatism (M-SIA) and the centroid of surgically induced astigmatism (C-SIA) after standard cataract surgery. Methods: We retrospectively examined 200 eyes of 100 consecutive patients undergoing bilateral cataract surgery through a 2.8 mm temporal clear corneal incision. We quantitatively measured the magnitude and axis of corneal astigmatism preoperatively and 3 months postoperatively using an automated keratometer (TONOREFF-II, Nidek). We assessed the M-SIA, the C-SIA, and the double angle plots for the display of the individual SIA distributions. Results: For bilateral data analysis, the magnitude of corneal astigmatism significantly increased from 0.66 +/- 0.39 D preoperatively to 0.74 +/- 0.46 D postoperatively (paired t-test, p = 0.012). The M-SIA was 0.50 +/- 0.36 D. On the other hand, the C-SIA was 0.18 +/- 0.60 D at an axis of 97 degrees. For unilateral analysis, we obtained similar outcomes between the right and left eye groups. Conclusions: According to our experience, standard cataract surgery induces the M-SIA by approximately 0.5 D. The magnitude of the C-SIA largely decreased to approximately 40% of the M-SIA, and the direction of the C-SIA showed a tendency toward with-the-rule astigmatism. It should be noted that the M-SIA was considerably different from the C-SIA, especially when selecting the appropriate toric IOL model and power.