Corneal Epithelial Thickness Intrasubject Repeatability and its Relation With Visual Limitation in Keratoconus

Abstract

Purpose: To evaluate intra-subject repeatability of anterior segment optical coherence tomography (AS-OCT) combined with placido disc MS-39 (CSO, Firenze, Italy) and correlate epithelial thickness measurements and the degree of visual limitation in keratoconus patients.

Design: Reliability analysis and cross-sectional study.

Methods: Setting: Vissum, Alicante, Spain.

Subjects: Total of 167 eyes, of which 107 were from keratoconus patients and 60 were healthy.

Procedures: Three repeated consecutive epithelial thickness measurements were taken: central 3.0 mm and the nasal, temporal, superior, and inferior regions at 3.0-6.0 mm and 6.0-8.0 mm.

Main outcome measures: Intrasubject repeatability of epithelial indices was assessed and correlated to the degree of best-corrected visual acuity (BCVA).

Results: The intraclass correlation coefficient was ≥0.90, indicating highly repeatable measurements for both keratoconus and healthy eyes. In multivariate analysis, epithelial indices associated with worse BCVA were as follows: thinner 3 mm central (P = .04), thicker 8 mm superior (P < .001), and thinner 8 mm inferior (P < .001). Thickness central 3 mm decreased as keratoconus grading increased (P = .002). The superior-inferior ratio at 8 mm significantly increased as keratoconus grading increased (P < .001). In multivariate analysis thinner 3 mm central (R² = 6.19%, P = .04), greater superior-inferior 8 mm ratio (R² = 8.37%, P = .004), greater superior-inferior 6mm ratio (R² = 2.67%, P = .02), and steeper K2 (R² = 21.51%, P < .001) were associated with keratoconus with a combined area under the curve of 0.92.

Conclusion: High repeatability of epithelial thickness measurements may be achieved in both keratoconus and healthy eyes with the MS-39. There is a significant correlation between epithelial thickness measurements and BCVA. These measurements may be of additional value in discriminating between keratoconus and healthy eyes.