To determine five year changes in corneal thickness from the apex to the 4mm periphery in 40-64 year olds through a longitudinal population-based Shahroud Eye Cohort Study.

Using Pentacam data of the first two phases, analysis was done on right eye data of 3422 people with no history of eye surgery and acceptable image quality. Thickness changes in different parts of the cornea and their relation with age, gender, refractive error, and intraocular pressure (IOP) were assessed.

Corneal thickness reduced by 1.1±11.7µm in the apex, 2.1±11.8 µm in the thinnest point, and 4.8±12.2 and 10.4±19.2µm in the 2 and 4mm peripheral rings, respectively (all p <0.001), all significantly different from each other. Changes were similar in both genders (p>0.05) except more thinning in women in the 4mm ring (-11.8±18.5µm vs. -8.1±20.0µm, P<0.001) and the thinnest point (-2.6±11.4µm vs. -1.5±12.3µm, P=0.014). Thickness changes were not related to refractive error or IOP (all p>0.05).

Corneal thickness decreased with age in this sample of 40-64 year olds. There was greater thinning in the periphery compared to the corneal center which can be associated with change in corneal shape and curvature. Inter-gender differences in this trend warrant further studies.