Stability of posterior corneal elevation one year after myopic laser in situ keratomileusis

Purpose: The aim was to describe the forward shift of the posterior corneal surface one year after myopic laser in situ keratomileusis (LASIK) relative to the estimated residual stromal bed thickness (RBT) and to correlate RBT with the ablation percentage per total corneal thickness (CT) in eyes without significant changes in anterior best-fit sphere (BFS) and corneal thickness one year after LASIK. Methods: The anterior and posterior BFS and central and peripheral corneal thickness were measured in 86 eyes from 43 patients (mean age 32.07 +/- 7.01 years), who underwent uneventful LASIK for myopia using Orbscan before and one, six and 12 months after LASIK. The patients were divided into three groups based on estimated RBT (Group 1 with 16 eyes [19%], RBT less than 250 mm, Group 2 with 52 eyes [58%], RBT from 250 to 300 mm and Group 3 with 20 eyes [23%], RBT greater than 300 mm) and into two groups based on ablation percentage (Group A, 52 eyes [60%], less than 20% and Group B, 34 eyes [40%], more than 20%). Results: The mean posterior forward shifting was 9.4 +/- 14.3 mm (range -27 to 80 mm) (p < 0.05), 4.0 +/- 9.8 mm (range -34 to 24 mm) (p > 0.05) and 3.1 +/- 8.8 mm (range -37 to 21 mm) (p > 0.05) at one, six and 12 months following LASIK, respectively. The posterior corneal forward shift was higher and showed an increasing trend in Group 1 (r(2) = 0.111), Group 2 (r(2) = 0.185) and Group B (r(2) = 0.156). Non-significant (p > 0.05) posterior elevation was found in Group 3. The anterior BFS and central and peripheral corneal thickness did not show statistically significant differences (p > 0.05) for all post-LASIK follow-up visits. Conclusions: The posterior corneal displacement measured with Orbscan after LASIK was time dependent, with a different trend between estimated residual stromal bed thickness that protruded at an early stage but then returned to original levels 12 months after LASIK in eyes without post-LASIK anterior topographic or pachymetric changes.