Comparison of corneal epithelial and stromal thickness and its distribution in keratoconus, ectasia susceptibility and healthy controls

Introduction
Optical coherence tomography (OCT) is a noncontact imaging modality which shows the corneal epithelial thickness (CET) pattern with high accuracy thanks to its high axial resolution� In the early diagnosis of ectatic disorders, measurement of CET and its distribution across the corneal surface is clinically important� In early ectasia, epithelial thinning on the cone apex may mask the topographical changes in the anterior corneal surface� We aimed to evaluate the variation in corneal epithelial and stromal thickness along with its distribution in eyes with keratoconus (KC), ectasia susceptibility (ES) and healthy controls�

Material & Methods
Subjects were recruited from extended sample of a population-based keratoconus (KC) prevalence study conducted at the Eskişehir Osmangazi University Hospital� Subjects were classified as KC, ES and normal based on Pentacam (Oculus)� Minimum and maximum epithelial (Min-ET and Max- ET) and stromal thickness (Min-ST and Max-ST) values along with their coordinate- wise locations were obtained from anterior segment OCT (Optovue Inc�) scans� Linear mixed model analysis with Bonferroni correction was used for across group comparisons� p<0�05 was considered statistically significant�

Results

A total of 896 subjects were included in the study, out of which 17 were KC, 16 were ES, and 863 were healthy� The mean age was 21�6 ± 2�4 years, and 65�8% (n=590) were female� Although minimum and maximum epithelial thicknesses were similar between healthy controls and ES, KC eyes showed significantly greater Max-ET and thinner Min-ET values (approximately 3 – 4μm, all p<0�05)� Likewise, minimum and maximum stromal thicknesses significantly deviated in eyes with KC from their counterparts in normal and ES groups (approximately 50 – 70μm, all p<0�05)� A 1 mm inferior and inferotemporal deviation in the thinnest stromal thickness location (reference: corneal apex) seemed to have increased the likelihood of KC presence by an odds ratio of 14�4 (p=0�01) and 57�3 folds (p=0�005), respectively�