Standardized Detection Of Keratoconus In Optical Coherence Tomography: Corneal And Epithelial Thickness Maps

To develop an algorithm for keratoconus detection by only analyzing the corneal and epithelial map parameters and patterns in optical coherence tomography (OCT).

Center for Refractive Surgery, Eye Department at St. Francis Hospital Muenster, Germany.

Corneal and epithelial thickness maps of normal, manifest, and subclinical keratoconic eyes (according to the Belin-Ambrosio display, Pentacam, Oculus) were evaluated by spectral domain OCT (Zeiss Cirrus 5000 HD). A novel two-step decision tree was developed based on previous studies with another OCT device. In the first step, if at least one of four independent parameters (pachymetry minimum, pachymetry minimum-median, pachymetry superonasal-inferotemporal, epithelial superonasal-inferotemporal) overrun the cutoff values, the eye was suspicious for keratoconus. In the second step, if epithelial map showed concentric thinning and the thinnest point of the cornea and the epithelium was coincident, the eye was classified as keratoconic. 

The study included 172 manifest keratoconic eyes (108 patients), 21 subclinical keratoconic eyes (20 patients), and 172 normal eyes (90 age-matched participants). Step 1 identified 100% of manifest and subclinical keratoconic eyes. Step 2 ruled out all suspicious but normal cases and falsely, 2 subclinical keratoconic eyes. Thus, our two-step decision tree reached 100% specificity, 100% sensitivity in manifest keratoconus and 90.4% sensitivity in subclinical keratoconus.

A novel algorithm was developed based on statistical cut-off values of various OCT derived parameters. Pachymetric and epithelial map parameters and patterns in OCT can be used in the diagnosis of keratoconus, including subclinical cases, yielding a high level of agreement with the current gold standard, the Belin-Ambrosio display. Further improvements by refining our algorithm and including an automated evaluation in the device software are desirable.