Changes in the anterior cornea during the early stages of severe myopia prior to and following LASIK, as detected by confocal microscopy

The present study aimed to assess the microscopic changes of the epithelium and Bowman's layer under confocal microscopy during the early stages of severe myopia following laser in situ keratomileusis (LASIK). The study comprised 54 patients (54 eyes) with severe myopia and 65 patients (65 eyes) with low and moderate myopia, who underwent LASIK surgery at Tianjin Medical University Eye Hospital (Tianjin, China). In all patients, the epithelium, Bowman's layer and anterior stroma were examined prior to and 1, 7, 30, 90 and 180 days after the surgery, using in vivo confocal microscopy. Six (6 eyes) of the 54 patients with severe myopia (11.1%) exhibited corneal epithelial changes following the surgery, as examined by a slit lamp. Three patients (3 eyes) exhibited epithelial changes under confocal microscopy. In 40 eyes (74.1%) with severe myopia, brown yellow changes were observed at the epithelial layer and in the central part of the cornea 6 months after the surgery; the same was observed in 35 eyes (53.8%) with low and moderate myopia. Microfolds in the Bowman's layer of eyes with severe myopia were detected in 48 eyes (88.9%), and in 54 eyes (100.0%) in the anterior stroma following LASIK, whereas microfolds were observed in 51 (78.5%) and 65 eyes (100%), respectively, in patients with low to moderate myopia. In the severe myopia group, 54 eyes (100%) exhibited nerve fibers below the epithelium that were detectable 1 day post-surgery; in 16 eyes (29.6%), 1 or 2 sub-epithelial nerve fibers were detected 7 days after the surgery, and in 24 eyes (44.4%), 1 or 2 sub-epithelial nerve fibers were observed 6 months after the surgery. In eyes with low and moderate myopia, the figures were 100, 38.5 and 64.8%, respectively. The nerves of neither group returned to the pre-operative level. In conclusion, neurotrophic epitheliopathy, microfolds in Bowman's layer and anterior stroma were detected in the present patients with severe myopia of the cornea following LASIK, and the recovery of nerve fibers required an extended period of time.