Posterior corneal surface changes after refractive surgery

Objective: To determine the frequency of changes in posterior corneal surfa ce after laser in situ keratomileusis (LASIK) and photorefractive keratecto my (PRK). Design: Nonrandomized, comparative trial. Participants: Ninety-five eyes (71 patients) that underwent PRK (n = 45) or LASIK (n = 50). Controls: Twenty nonsurgery eyes were used to validate the method of analys is of the posterior corneal curvature (PCC). Seventy nonsurgery eyes were u sed for comparisons. Methods: Float, apex-fixed best fit corneal curvature (ABC), and posterior elevation difference were evaluated in 20 elevation topography maps at 6 zo ne 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 a nd compared with a nonsurgery group. Main Outcome Measures: Posterior corneal curvature change (mm) was classifi ed as flattening, steepening, or no change. Results. 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 LA SIK 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 ch ange in 40% of eyes (n = 20), and steepening in 30% of eyes (n = 15). The n onsurgery group showed a similar change in PCC at two different time points similar to that of the PRK and the LASIK groups. Conclusions: The differences observed in the PCC after PRK or LASIK were no t statistically significantly different from those observed over time in th e nonsurgery control group. Ophthalmology 2001;108:1415-1422 (C) 2001 by th e American Academy of Ophthalmology.