Posterior corneal surface changes after refractive surgery

To determine the frequency of changes in posterior corneal surface after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Nonrandomized, comparative trial. Ninety-five eyes (71 patients) that underwent PRK (n = 45) or LASIK (n = 50). Twenty nonsurgery eyes were used to validate the method of analysis of the posterior corneal curvature (PCC). Seventy nonsurgery eyes were used for comparisons. Float, apex-fixed best fit corneal curvature (ABC), and posterior elevation difference were evaluated in 20 elevation topography maps at 6 zone diameters (3–7 and 10 mm) and at two time points. Corneal elevation maps before and after PRK or LASIK were analyzed by the ABC and float methods and compared with a nonsurgery group. Posterior corneal curvature change (mm) was classified as flattening, steepening, or no change. Flattening of more than 0.12 mm was found in 22.2% of eyes (n = 10) in the PRK group, a change of ±0.12 mm was found in 53.3% of eyes (n = 24), and steepening of more than 0.12 mm was found in 24.4% of eyes (n = 11) using the float method and in 28.9% of eyes (n = 13), 35.6% of eyes (n = 16), and 35.6% eyes (n = 16), respectively, using the ABC method. In the LASIK group, the float method registered flattening in 20% of eyes (n = 10), no change in 52% of eyes (n = 26), and steepening in 28% of eyes (n = 14), whereas the ABC method registered flattening in 30% of eyes (n = 15), no change in 40% of eyes (n = 20), and steepening in 30% of eyes (n = 15). The nonsurgery group showed a similar change in PCC at two different time points similar to that of the PRK and the LASIK groups. The differences observed in the PCC after PRK or LASIK were not statistically significantly different from those observed over time in the nonsurgery control group.