Pterygia as cause of post-cataract with-the-rule astigmatism.

Pterygia often induce with-the-rule astigmatism as they invade the cornea. Significant amounts of astigmatism occur long before a pterygium encroaches on the visual axis. We present an example in which a 3.3-mm pterygium resulted in 9 diopters (D) of with-the-rule astigmatism. Six weeks after the pterygium removal, the patient's cornea became spherical, but by three months the pterygium had recurred 2.2 mm onto the cornea and induced 4 D of with-the-rule astigmatism. Since the second removal and the application of beta irradiation, there has been no recurrence. The final correction was -1.00 + 1.00 X 127 degrees with a visual acuity of 20/20 +3. Characteristic keratoscopic photographs are shown and contrasted with surgically induced with-the-rule astigmatism.