we have introduced and reported   a potential novel clinical indicator for keratoconus ( kcn ) cornea instability assessment based on consistent , increased overall corneal epithelial thickness . as in our previous report , most epithelial measurements have been performed in vivo , by high - frequency scanning ultrasound biomicroscopy ( hf - ubm ) . we report herein similar data using anterior segment optical coherence tomography ( as - oct ) . we present the case of a 25-year - old male subject , diagnosed with topographic and topometric asymmetrically manifested kcn among his two eyes . 170. corrected distance visual acuity with this prescription was 20/20 + . the left eye ( os ) , the more symptomatic one , had an uncorrected distance visual acuity of 20/80 and a manifest refraction 7.00 3.50 the kcn diagnosis was further confirmed by corneal tomography imaging , obtained by wavelight oculyzer ii ( alcon surgical , ft . , usa ) which is a pentacam hr ( high - resolution ) scheimpflug imaging camera [ 2[ga1 ] ] . four consecutive corneal scans in each eye were obtained by as - oct rtvue-100 ( optovue inc . , examples of od and os epithelial pachymetry maps ( 6 mm diameter ) are provided in fig . repeatability , which can be assessed by the standard deviation of the central epithelium of the 4 scans , was 0.60 and 1.50 m in od and os , respectively . 2a , od had a central epithelial thickness ( epi ct ) of 52.23  0.60 m . overall epithelial thickness ( epi average ) was computed by taking the average of the 17 segment thickness points shown in fig . 1c , d. the values displayed in each of the 17 segments are the average of the epithelial thickness measurements within each segment . od had an epi average of 51.97  0.70 m . os had an epi ct of 56.75  1.50 m and an epi average of 55.65  1.22 m . the epithelial topographic thickness variability ( epi variability , fig . our results show that on average , the epi variability was 1.53  0.21 m for the less affected od , while it was 9.80  0.41 m for the more affected os . hf - ubm has known intrinsic examiner operative challenges ( both for capture and interpretation ) , and although available for over a decade , it has seen very little clinical use and mainstream practice acceptance . clinical availability of corneal epithelial mapping by as - oct is currently in practice , and introduces a simple and effective clinical tool for corneal epithelial mapping . the data are very easily captured and epithelial thickness parameters are automatically calculated by a novel software algorithm and presented in topographic imaging [ 3 , 4 ] . this case illustrates a vivid agreement with previous findings by kanellopoulos et al .   that an overall thicker epithelium with large variations can be observed in the topographically evident kcn eye , and to a much lesser degree in the less affected eye . qualitatively , the defining feature of the epithelium in kcn is the pattern , such that there is a thin epithelium over the cone surrounded by a thicker epithelium  as can be seen in fig . 1d . quantitatively , epithelial thickness variations can be expressed as the topographic thickness variability and are computed by the standard deviation of the 17 segment thickness points . specifically , in our case , it was  9.80 m in the affected kcn eye and  1.53 m in the less affected eye . in fig . 2b , the graph compares the corresponding values of epithelial thickness from the hf - ubm study   and the case described herein . this case not only confirms our findings regarding the increased overall epithelial thickness in ectatic eyes , but also that the new as - oct feature of epithelial imaging may illustrate these differences in a more pronounced way , as indicated by the data shown in fig . the ease of use of as - oct epithelial imaging in comparison to hf - ubm as well as the increased predictability that may be offered by as - oct epithelial imaging may hold promise for wider clinical application , such as the screening of young adults for early kcn and , in a much wider perspective , potential candidates for laser cornea refractive surgery .