Corneal Epithelial Thickness Maps in Eyes with Mild and Moderate Keratoconus.

Background/

Objectives

The evaluation of the differences in corneal epithelial thickness profiles in healthy eyes and eyes with mild and moderate stages of keratoconus, using optical coherence tomography (OCT).

Methods

Fifty-two healthy eyes (group 0), forty-one eyes with mild keratoconus (group I), and thirty eyes with moderate keratoconus (group II) were included in this study. Only one of the patient's eyes was enrolled, and they were divided into groups using the Amsler-Krumeich (A-K) classification-stage I and II. All patients underwent a visual acuity assessment, slit-lamp examination, corneal tomography, and automatic mapping of corneal thickness and epithelial thickness on a diameter of 9 mm. Corneal tomography with a Placido/Scheimpflug instrument (Sirius, CSO, Florence, Italy) and OCT with a corneal adaptor module (Avanti RTVue XR, Optovue, Lombard, IL, USA) were used.

Results

Minimum corneal epithelium thickness was 49.5, 43, and 40 µm in groups 0, I, and II, respectively (Kruskal-Wallis test, p < 0.001). A moderate correlation was found between minimum epithelial thickness and the apex curvature (Pearsons's coefficient r = -0.62, p < 0.001) and posterior radius of central corneal curvature (Pearsons's coefficient r = 0.62, p < 0.001). The difference between minimum and maximum epithelial thickness showed a high correlation (r = -0.770, p < 0.001). In groups I and II, on corneal epithelial thickness maps the thinnest sector, located inferiorly and temporally to the center, was surrounded by sectors with increased thickness.

Conclusions

At the apex of the cone, the corneal epithelium becomes thinner, and a thicker ring forms around the cone. Although there is a moderate-to-strong correlation to parameters linked with the severity of keratoconus, and minimum epithelial thickness as well as the minimum-maximum difference, it is not possible to establish cut-off values for stages I and II in the Amsler-Krumeich (A-K) classification.