Inclusion criteria for the study focused on patients over 34 (range from 34 to 41) with stable corneal topography and refraction for at least six months and an estimated residual bed thickness of >410 µm.  exclusion from the study included the presence of macular or retinal disease, dry eye, history of recurrent corneal erosions, anterior segment abnormalities, unstable refractive error, post-surgically residual stromal bed thickness of under 350 mm, autoimmune disease, collagen vascular disease, immunosuppressive therapy, or current use of systemic corticosteroids, diabetes mellitus, pregnancy, and lactation.