Corneal epithelium is altered in keratoconus and forme fruste keratoconus

This study investigated the corneal epithelial thickness and its distribution in keratoconus (KC) and forme fruste keratoconus (FFK). We recruited 144 KC eyes and 27 FFK eyes from 76 participants (50 men and 26 women) who underwent anterior segment-optical coherence tomography from April 2020 to September 2023 at the International University of Health and Welfare Narita Hospital. There were 42 age- and sex-matched controls. Corneal epithelial thickness and its distribution in the central, paracentral, and peripheral areas were statistically investigated. Each area was divided into eight zones. The minimum, maximum, and average epithelial thicknesses were thinner in KC eyes in the inferior-nasal, inferior, and inferior-temporal zones. Standard deviations were significantly greater in KC eyes in almost all zones. In FFK eyes, the minimum and average epithelial thicknesses of the inferior and inferior-temporal zones were significantly thinner in the paracentral area. Changes in standard deviations were almost limited in the paracentral area. According to the Amsler–Krumeich classification, the more severe the stage, the thinner the corneal thickness in patients with KC. Although the difference between superior and inferior thickness increased in both KC and FFK eyes, it decreased with KC severity. However, the superior-inferior differences increased in the peripheral area. Epithelial thickness and distribution were altered in KC eyes and even in FFK eyes with normal topography. Nevertheless, there may be differences in the epithelial changes between the early stage and the advanced stage of KC.