Purpose
To use anterior-segment optical coherence tomography (AS-OCT) to investigate epithelial thickness distribution characteristics in keratoconic patients
Methods
The study group (A) consisted of 160 eyes with clinically diagnosed keratoconus and the control group (B) was composed of 160 non-keratoconic eyes. Employing anterior-segment OCT (RtVue-100, Optovue, Fremont, CA), three successive acquisitions were performed in each eye. 3-dimensional epithelial thickness maps were obtained, enabling investigation of epithelial thickness at the pupil center, mid-periphery, superior and inferior cornea. These data provided the average, maximum, minimum, and topographic epithelial thickness variability. Intra-individual variation of epithelial thickness measurement was also evaluated. We further investigated correlation of the epithelial data via newly defined Scheimpflug imaging-derived anterior-surface irregularity indices for keratoconus severity: the index of height decentration (IHD) and the index of surface variance (ISV). The epithelial thickness indices were then correlated with these two indices.
Results
The average intra-individual epithelial thickness repeatability was 1.67μm in Group A (keratoconic group) and 1.13μm in Group B (control group). The pupil center epithelial thickness was 51.75±7.02 μm in the keratoconic group, and maximum and minimum thickness were 63.54±8.85 μm and 40.73±8.51 μm. In the control group, epithelial thickness at the center was 52.54±3.23 μm, maximum thickness was 55.33±3.27 μm and the minimum was 48.50±3.98 μm. Topographic variability was 6.07±3.55 μm in the keratoconic group, while 1.59±0.79 μm in the control group. Both epithelial thickness variability and range, defined as minimum-maximum, correlated tightly with the indices of IHD and ISV.
Conclusions
AS-OCT offers both ease of use and high predictability in assessing in-vivo epithelial thickness measurement in keratoconus. We have demonstrated that keratoconic eyes have an increased overall epithelial thickness as compared to normal eyes and that there exists a tight correlation between increased topographic thickness variability and range and keratoconus severity. Because epithelial thickness as measured by AS-OCT may be used to identify and assess mild and suspected cases of keratoconus, this technique is of particular clinical importance.