Induced astigmatism and its decay with a frown incision.

Forty consecutive patients selected for cataract extraction by phacoemulsification were studied to evaluate prospectively the amount of and changes in surgically induced astigmatism from a 5 mm to 6 mm pocket incision with the external opening made convex against the limbus (frown incision). All incisions had an internal corneal valve and were closed by a single X-stitch to counteract the relaxing effect of the pocket in the 90-degree meridian. Surgically induced astigmatism calculated by simple subtraction was 0.64 +/- 0.90 diopters (D) (P < .0001) on the first postoperative day, 0.03 +/- 0.58 D (P = .75) six weeks after surgery, and -0.18 +/- 0.44 D (P = .01) six months after surgery. Calculated from polar equivalents, the induced astigmatism on the first postoperative day was 0.98 D +/- 1.03 D (P = .0001), after six weeks -0.11 D +/- 0.64 D (P = .30), and after six months -0.28 D +/- 0.49 D (P = .0009). On the first postoperative day 42% of eyes had less than 0.5 D of induced astigmatism, 68% had less than 1.0 D, and 79% had less than 1.5 D. After six weeks the respective percentages increased to 61%, 97%, and 97% and after six months to 84%, 100%, and 100%. The distribution of patients with against-the-rule, oblique, and with-the-rule astigmatism preoperatively was nine, 20, and 11, respectively, and 11, 19, and nine after six months. The amount of astigmatism induced from the 5 mm to 6 mm frown incision did not differ from that found in previously published studies of smaller incisions (to about 4 mm).(ABSTRACT TRUNCATED AT 250 WORDS)