Refractive outcome of radial keratotomy: Does the result of the first eye predict outcome in the second eye?

PURPOSE: To present a method of quantifying variability in the outcome of a refractive surgical procedure using the SD of the difference between achieved and expected refractive changes. We used this method to determine whether the refractive outcome of radial keratotomy in a first eye is predictive of outcome in the second eye. METHODS: We retrospectively identified patients who underwent eight incision radial keratotomy in the first eye from February 1993 through April 1994, with follow-up refraction 2.5 to 5 months postoperatively. This group consisted of 129 eyes of 81 patients. Thirty-nine patients had bilateral surgery with appropriate follow-up. Achieved refractive change was analyzed by multivariate linear and nonlinear regression to yield an expected refractive change for each eye based on patient age and optical zone size. RESULTS: Residuals, defined as the difference between the achieved and expected refractive change, were normally distributed. The SD of the residuals was 0.68 diopter and was independent of the expected correction. The prediction of second-eye refractive change was not significantly improved by incorporating the residual from the first eye into the regression prediction. CONCLUSIONS: The SD of the difference between the achieved and expected refractive change is an appropriate measure of the variability in refractive outcome following a refractive surgical procedure. Surgeons who perform bilateral simultaneons radial keratotomy do not sacrifice refractive accuracy in the second eye.