A five-year follow-up study of posterior corneal curvature and central corneal thickness after LASIK using Orbscan II

Abstract

Objective To study the long-term (five-year follow-up) changes in posterior corneal curvature and central comeal thickness by using the Orbscan Ⅱ topographer in patients who had undergone laser in situ keratomileusis (LASIK) for myopia.Methods Forty-eight eyes of 48 patients who had undergone LASIK for myopia were included in a retrospective observational case series study.The mean preoperative refractive error was-6.25±2.87 D.The preoperative and postoperative changes in the posterior corneal curvature and central comeal thickness of each eye were measured by Orbscan Ⅱ.The posterior corneal curvature was obtained from the central 6mm zone of the Orbscan Ⅱ.The postoperative follow-up period was at 1,3,6,9,12,24,36 and 60 months.Using SPSS 16.0 software,a comparison of the least-significant difference (LSD) pairwise was used to analyze the difference in the posterior corneal curvature and central corneal thickness at each follow-up visit.Results ①The posterior corneal curvature was higher in the 1st month postoperatively compared to preoperative curvature (t=8.211,P＜0.01).There was no statistically significant difference for the change in posterior corneal curvature from the 1st month to the 9th month (P＞0.05).The posterior corneal curvature slowly decreased over time from the 9th month to the 24th month (the values of t were-4.640 and-2.659,the values of P were ＜0.001 and 0.014).The posterior corneal curvature did not become stable until after the 24th month (P＞0.05).②The central corneal thickness was lower in the 1st month postoperatively than preoperative thickness (t=10.08,P＜0.01).The central corneal thickness slowly increased over time from the 1st month to the 9th month (the values of t were-5.402,-4.428 and-2.334,the values of P were ＜0.001,＜0.001 and 0.027).The central corneal thickness did not become stable until after the 9th month (P＞0.05).③The posterior corneal curvature was correlated with corneal thickness (r=-0.703,P＜0.01).Conclusion The posterior corneal curvature and the central corneal thickness both increase shortly after LASIK surgery and stabilize after this initial period.There is a negative correlation between posterior corneal curvature and central corneal thickness. Key words: Keratomileusis,laser in situ ; Posterior corneal curvature; Corneal thickness ; Corneal topography; Follow-up