Trapezoidal keratotomy. A vector analysis.

Twenty-three eyes in 23 patients ranging from 61 to 83 years of age underwent trapezoidal astigmatic (Ruiz) keratotomy. Preoperative regular astigmatism ranged from 3.13 to 13.00 diopters by keratometry. Fourteen of the eyes had high regular astigmatism following penetrating keratoplasty, eight following cataract extraction, and one eye had no history of surgery. Patient follow-up ranged from 1 to 15 months with a mean of five months. Trigonometric vector analysis of the keratometric readings demonstrated that the magnitude of surgically induced change in corneal curvature was inversely proportional to the size of the optical zone and ranged from 1.28 to 14.21 diopters. Frequently, due to the axis of surgically induced change, the magnitude of change in corneal curvature failed to be reflected by an equal magnitude of reduction in the residual corneal astigmatic error, and in many cases a residual error was created in a meridian differing significantly from that of the preoperative astigmatic error. There is no statistically significant difference in the slopes of the linear regression lines relating change in corneal curvature to optical zone size between this series and our previously reported cadaver study.