Noncontact measurements of central corneal epithelial and flap thickness after laser in situ keratomileusis

PURPOSE. To investigate the changes in the epithelium and flap after laser in situ keratomileusis (LASIK), when measured with optical coherence tomography (OCT). METHODS. Twenty-eight eyes of 14 patients (age: 39.9 ± 8.6 years) underwent LASIK. The central thickness of corneal epithelium and flap were measured with a real-time 1310 nm OCT 1 day, 1 week, and 1 month after surgery. A custom software program was used to process multiple images of each eye on each visit. RESULTS. After surgery, the corneal epithelium changed significantly (ANOVA: F_{(3, 81)} = 12.3, P = 0.000) with not statistically significant thinning at one day (mean ± SD: 57.8 ± 5.9 μm, P = 0.26, compared with baseline: 59.9 ± 5.9 μm) and statistically significant thickening at 1 week (60.8 ± 5.8 μm, P = 0.04, compared with 1 day) and 1 month (64.6 ± 6.1 μm, P = 0.008 compared with all others). There were statistically significant changes in the corneal flap thickness (ANOVA: F_{(2, 54)} = 4.59, P = 0.01) with thickening in the intervals between 1 day (143.3 ± 20.6 μm) and 1 week (149.7 ± 24.6 μm, P = 0.12), and between 1 week and 1 month (152.7 ± 19.3 μm, P = 0.01). There was a strong correlation (r = 0.898) between the difference of corneal thickness before and after surgery and predicted laser ablation depth. CONCLUSIONS. OCT is a useful noncontact tool for thickness measurements of the epithelium, flap, and total cornea. After LASIK, the epithelium and flap showed thickening during the study period.