SD-OCT analysis of regional epithelial thickness profiles in keratoconus, postoperative corneal ectasia, and normal eyes

Abstract

Purpose: To assess corneal microarchitecture and regional epithelial thickness profile in eyes with keratoconus, postoperative corneal ectasia (ectasia), and normal unoperated eyes (controls) using spectral-domain optical coherence tomography (SD-OCT).

Methods: Regional corneal epithelial thickness profiles were measured with anterior segment SD-OCT (Optovue RTVue-100, Optovue Inc., Fremont, CA). Epithelial thickness was assessed at 21 points, 0.5 mm apart, across the central 6-mm of the corneal apex in the horizontal and vertical meridians.

Results: One hundred twenty eyes were evaluated, including 49 eyes from 29 patients with keratoconus, 32 eyes from 16 patients with ectasia, and 39 eyes from 21 control patients. Average epithelial thickness at the corneal apex was 41.18 ± 6.47 μm (range: 30 to 51 μm) for keratoconus, 46.5 ± 6.72 μm for ectasia (range: 34 to 60 μm), and 50.45 ± 3.92 μm for controls (range: 42 to 55 μm). Apical epithelial thickness was significantly thinner in eyes with keratoconus (P < .0001) and ectasia (P = .0007) than in controls. Epithelial thickness ranges in all other areas varied widely for keratoconus (range: 21 to 101 μm) and ectasia (range: 30 to 82 μm) compared to controls (range: 43 to 64) (P = .0063).

Conclusion: SD-OCT demonstrated significant central and regional epithelial thickness profile differences between keratoconus, ectasia, and control eyes, with significant variability and unpredictability in ectatic eyes. This regional irregularity may necessitate direct epithelial thickness measurement for treatments where underlying stromal variations may be clinically relevant, including corneal collagen cross-linking or topography-guided ablations.

Figure 1

Spectral-domain OCT anatomical landmarks for epithelium-Bowman layer interface.

Figure 2

Cornea epithelial thickness across the central 6-mm of the corneal apex in the (A) vertical and (B) horizontal meridian in normal eyes, keratoconus and postoperative corneal ectasia. *p < .05 (ANOVA, JMP® 9.0 - SAS Institute Inc.)

Figure 2

Cornea epithelial thickness across the central 6-mm of the corneal apex in the (A) vertical and (B) horizontal meridian in normal eyes, keratoconus and postoperative corneal ectasia. *p < .05 (ANOVA, JMP® 9.0 - SAS Institute Inc.)

Figure 3

Relationship between spectral-domain OCT cross-sectional high resolution scans across the central 6-mm of the corneal apex in the vertical meridian and Scheimpflug imaging (sagittal curvature and regional thickness mapping) in mild (Fig. 3 A and B), moderate (Fig. 3 C and D), and severe (Fig. 3 E and F) keratoconus. Irregularities of the corneal epithelium and localized area of thickened epithelium are observed.