Effect of incision direction on refractive outcome after radial keratotomy Gerald W. Flanagan, OD, Perry S. Binder, MD ABSTRACT Purpose: To determine whether the direction of radial keratotomy (RI<) incisions (centripetal versus centrifugal) affects refractive outcome. Setting: Private ophthalmology office. Methods: The database of a single surgeon was retrospectively reviewed. Stepwise regression was used to select significant predictors of refraction change in the population. In addition to incision direction, variables evaluated were optic zone diameter, number of incisions, patient age, corneal curvature, and planned incision depth. Results: All variables except planned incision depth and corneal power affected refractive outcome. After controlling for number of incisions, optic zone diameter, and patient age, centripetal incisions decreased myopia 0.87 diopters more than centrifugal incisions. Conclusion: Our results, consistent with previous investigations, found that number of incisions, optic zone diameter, and patient age were significant predictors of refractive outcome after RK. Incision direction was also a significant predictor by itself or coupled with optic zone diameter and number of incisions, with the centripetal incision decreasing myopia more. J Cataract Refract Surg 1996; 22: 915-923 W hen introduced in the United States, radial ker- atotomy (RK) was performed using razor blade fragments adjusted under the operating microscope against a linear block gauge; corneal thickness was mea- sured by optical pachymetry. I As many as 32 incisions were made, beginning in the limbus, crossing the vascu- lar arcade in a centripetal (uphill) direction, and con- tinuing the incision to the edge of optical clear zone diameters as small as 2.5 mm. 1 Evaluation of Radial Keratotomy (PERK) study,2 inci- sion direction was changed to centrifugal (downhill). The goal was to increase safety by avoiding the risk of incisions in the visual axis. 2 The PERK and other stud- ies 3 - 6 found that patient age, number of incisions, and incision length and depth are the major determinants of refractive outcome. In hopes of improving refractive outcome and un- der the influence of Leo Bores, MD, and the Prospective From the Ophthalmology Research Laboratory of the National Vision Research Institute, San Diego, California. Reprint requests to Perry S. Binder, MD, Vision Surgery and Laser Center, 8910 University Center Lane, San Diego, California 92122. Centripetal incisions create significantly deeper wounds than centrifugal incisions performed by the same surgeon with the same blade extension? The deeper wounds are created by mechanical factors inher- ent in the cornea and the anatomy of the diamond blade,8,9 suggesting that refractive effect would be greater for the same number of incisions. Clinical studies have found that greater refractive results are obtained . h . al' .. 10 II B k 1 d h 12 Wit centnpet InCISlOns.' er e eyan coaut ors J CATARACT REFRACT SURG-VOL 22, SEPTEMBER 1996 915