Influence of excimer laser photorefractive keratectomy on the posterior corneal surface

Purpose: To investigate the influence of excimer laser photorefractive keratectomy on the refraction and geometry of the posterior corneal surface. Setting: Miyata Eye Hospital, Miyazaki, Japan. Methods: Thirty-seven eyes of 21 patients with refractive errors of -2.00 to -9.75 diopters (D) were treated with the VISX Twenty-Twenty excimer laser system. The refractive and anteroposterior changes in the posterior corneal surface were measured using scanning-slit corneal topography (Orbscan, Orbtek, inc.) preoperatively and 1 week and 1 and 3 months postoperatively. Results: Mean posterior corneal refraction was -6.51 D +/- 0.29 (SD) preoperatively; it decreased to -7.00 +/- 0.49 D, -7.00 +/- 0.55 D, and -6.92 +/- 0.42 D at 1 week, 1 month, and 3 months, respectively (P < .001, Tukey multiple comparison). Mean forward shift of the posterior corneal surface was 29.5 +/- 1.9 mu m, 34.4 +/- 3.4 mu m, and 54.3 +/- 4.0 pm at 1 week, 1 month. and 3 months, respectively. The amount of posterior corneal refractive change correlated with the degree of forward shift: (r = -0.691, P < .001). The residual corneal thickness correlated with the refractive change (r = 0.524, P < .001) and the forward shift (r = -0.851, P < .001) of the posterior corneal surface. Conclusion: Photorefractive keratectomy induced significant refractive changes in the posterior corneal surface and forward shift of the cornea, both of which correlated with the thinness of the residual cornea. (C) 2000 ASCRS and ESCRS.