To compare topographic, pachymetric and epithelial distribution patterns of clinically unaffected fellow eyes of patients with asymmetric keratoconus (AKC) with those of normal controls and keratoconic fellow eyes.

A prospective, observational study was conducted at a tertiary care center, in which twenty-five clinically unaffected fellow eyes in patients with AKC were compared to 25 keratoconic fellow eyes and 67 normal controls. Pachymetric and epithelial thicknesses in the central 2 mm and 8 octants in the 2–5 mm and 5–7 mm zones were compared using Spectral Domain Optical Coherence Tomography (SDOCT). Scheimpflug derived topography was also compared.

Mean simulated keratometry of fellow eyes (43.6D ± 1.34 D) was comparable to that of control eyes (43.85D ± 1.57 D) (p > 0.99) and less than that of keratoconic eyes (47.08D ± 4.62 D) (p = 0.004). Central corneal and epithelial thicknesses of fellow eyes (474.28 ± 40.27 μm, 52.76 ± 7.45 μm, respectively) were less than in control eyes (505.97 ± 30.12 μm, 60.48 ± 8.37 μm) (p < 0.001 and p = 0.006, respectively) but comparable to those of keratoconic eyes (470.48 ± 44.19 μm, 52.48 ± 8.00 μm) (p > 0.99). Pachymetric differences of radially opposite octants in the 2–5 mm zone demonstrated thinning in the inferior and inferotemporal octants of fellow eyes which was greater than that seen in control eyes (p = 0.017 and 0.04, respectively)

Reduced central epithelial thickness and greater pachymetric differences in radially opposite octants of the mid-peripheral cornea may be suggestive of susceptibility to ectasia despite normal topography.