Role of epithelial mapping in the differentiation between early keratoconus and high regular astigmatism using spectral-domain optical coherence tomography

Abstract

Pur6pose To detect epithelial thickness-based diagnostic variables to detect early keratoconus (KC) and differentiate cases of early KC from high regular astigmatism, especially if abnormal topographic changes are present. Patients and methods A total of 84 eyes with high regular astigmatism on Scheimpflug imaging were evaluated by anterior segment optical coherence tomography (AS-OCT). Imaging of the cornea as well as pachymetry and epithelial thickness mapping was done using AS-OCT via a special lens mounted to a tomographic device. The same was done using Scheimpflug imaging (CSO Sirius device). Thickness of the corneal epithelium was automatically mapped using a computer algorithm. Calculations of the following diagnostic factors were recorded: minimum, superior–inferior, minimum–maximum, root-mean-square variation, root-mean-square pattern deviation, and thickness of the zonal epithelium. Results This study analyzed 84 eyes divided into two groups: group A (n=56 eyes) had high regular astigmatism and group B (n=28 eyes) with early KC. The mean spherical refraction, cylindrical refraction, and central corneal thickness (Scheimpflug imaging) for group A were −1.16±1.02 D, −3.67±0.67, and 542.88±29.64 μm, respectively. In group A, the mean central corneal thickness and central epithelial thickness was 538.84±29.67 and 52.34±1.69 μm, respectively. The mean spherical refraction, cylindrical refraction, central corneal, and epithelial thickness mean for group B were −1.75±0.87, −4.02±0.69 D, 505.36±28.48, and 49.93±0.9 μm, respectively. A significant correlation between central epithelial thickness with anterior elevation was noted in group B (P=0.048). Conclusion AS-OCT epithelial mapping may prove to be a useful diagnostic tool for determining early development of KC.