Post-LASIK Ectasia Versus Keratoconus: An In Vivo Confocal Microscopy Study

PURPOSE: To examine and compare corneal cellular and subbasal nerve (SBN) characteristics in post-laser-assisted in situ keratomileusis ectasia (PLE) corneas, normal post-laser-assisted in situ keratomileusis corneas (PLC), keratoconus (KC) corneas, and normal virgin corneas (NC). METHODS: In this cross-sectional comparative study, 18 PLE eyes of 11 patients, 18 PLC of 15 cases, 32 KC eyes of 32 patients, and 29 NC of 29 subjects were assessed using in vivo confocal microscopy. The density of the basal epithelial cell (BEC), anterior keratocyte, posterior keratocyte, and endothelial cell layers, as well as the characteristics of SBN fibers, was compared between the 4 groups. RESULTS: The density of the BEC and anterior and posterior keratocyte layers was significantly lower in KC compared with NC (-650 ± 190, P = 0.013; -181 ± 39, P < 0.001; and -36 ± 11, P = 0.021, respectively). However, there was no significant difference between PLE and PLC regarding these parameters (all Ps � 0.6). Mean SBN parameters, including central corneal nerve branch density, nerve fiber length, total branch density, and nerve fiber area, were significantly lower in KC compared with NC and in PLE compared with PLC (all Ps � 0.021). CONCLUSIONS: The pathophysiology of PLE seems to differ from KC. Apparent changes in the BEC and anterior and posterior keratocytes associated with KC were not observed in PLE. However, SBNs seem to be involved in both conditions