Objective To map the corneal epithelial thickness with Fourier-domain optical coherence tomography (OCT) and develop epithelial thickness-based variables for keratoconus detection. Design Cross-sectional observational study. Participants One hundred forty-five eyes from 76 normal subjects and 35 keratoconic eyes from 22 patients. Methods A 26,000 Hz Fourier-domain OCT system with 5-μm axial resolution was used. The cornea was imaged with a “Pachymetry+Cpwr” scan pattern (6-mm scan diameter, 8 radials, 1024 axial-scans each, repeated 5 times) centered on the pupil. Three scans were obtained at a single visit in a prospective study. A computer algorithm was developed to automatically map the corneal epithelial thickness. Zonal epithelial thicknesses and 5 diagnostic variables, including minimum, superior–inferior (S-I), minimum–maximum (MIN-MAX), root-mean-square variation (RMSV), and root-mean-square pattern deviation (RMSPD), were calculated. Repeatability of the measurements was assessed by the pooled standard deviation. The area under the receiver operating characteristic curve (AROC) was used to evaluate diagnostic accuracy. Main Outcome Measures Descriptive statistics, repeatability, and AROC of the zonal epithelial thickness and diagnostic variables. Results The central, superior, and inferior epithelial thickness averages were 52.3±3.6, 49.6±3.5, and 51.2±3.4 μm in normal eyes and 51.9±5.3, 51.2±4.2 and 49.1±4.3 μm in keratoconic eyes. Compared to normal eyes, keratoconic eyes had significantly lower inferior (p = 0.03) and minimum corneal epithelial thickness (p < 0.0001), greater S-I (p = 0.013), more negative MIN-MAX (p < 0.0001), greater RMSV (p < 0.0001), and larger RMSPD (p < 0.0001). The repeatability of the zonal average, minimum, S-I, MIN-MAX epithelial thickness variables were between 0.7 to 1.9 μm. The repeatability of RMSV was better than 0.4 μm. The repeatability of RMSPD was 0.02 or better. Among all epithelial thickness based variables investigated, RMSPD provided the best diagnostic power (AROC = 1.00). Using a RMSPD cutoff value of 0.057 alone gave 100% specificity and 100% sensitivity. Conclusions High-resolution Fourier-domain OCT mapped corneal epithelial thickness with good repeatability in both normal and keratoconic eyes. Keratoconus was characterized by apical epithelial thinning. The resulting deviation from the normal epithelial pattern could be detected with very high accuracy using the RMSPD variable.

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Objective To detect abnormal corneal thinning in keratoconus using pachymetry maps measured by high-speed anterior segment optical coherence tomography (OCT). Design Cross-sectional observational study. Participants Thirty-seven keratoconic eyes from 21 subjects and 36 eyes from 18 normal subjects. Methods The OCT system operated at a 1.3 μm wavelength with a scan rate of 2000 axial scans per second. A pachymetry scan pattern (8 radials, 128 axial scans each; 10 mm diameter) centered at the corneal vertex was used to map the corneal thickness. The pachymetry map was divided into zones by octants and annular rings. Five pachymetric parameters were calculated from the region inside the 5 mm diameter: minimum, minimum–median, inferior–superior (I-S), inferotemporal–superonasal (IT-SN), and the vertical location of the thinnest cornea. The 1-percentile value of the normal group was used to define the diagnostic cutoff. Placido-ring–based corneal topography was obtained for comparison. Main Outcome Measures The OCT pachymetric parameters and a quantitative topographic keratoconus index (keratometry, I-S, astigmatism, and skew percentage [KISA%]) were used for keratoconus diagnosis. Diagnostic performance was assessed by the area under the receiver operating characteristic (AROC) curve. Results Keratoconic corneas were thinner. The pachymetric minimum averaged 452.6±60.9 μm in keratoconic eyes versus 546±23.7 μm in normal eyes. The 1-percentile cutoff was 491.6 μm. The thinnest location was inferiorly displaced in keratoconus (−805±749 μm vs −118±260 μm ; cutoff, −716 μm). The thinning was focal (minimum–median: −95.2±41.1 μm vs −45±7.7 μm ; cutoff, −62.6 μm). Keratoconic maps were more asymmetric (I-S, −44.8±28.7 μm vs −9.9±9.3 μm ; cutoff, −31.3 μm ; and IT-SN, −63±35.7 μm vs −22±11.4 μm ; cutoff, −48.2 μm). Keratoconic eyes had a higher KISA% index (2641±5024 vs 21±19). All differences were statistically significant (t test, P<0.0001). Applying the diagnostic criteria of any 1 OCT pachymetric parameter below the keratoconus cutoff yielded an AROC of 0.99, which was marginally better (P= .09) than the KISA% topographic index (AROC, 0.91). Conclusions Optical coherence tomography pachymetry maps accurately detected the characteristic abnormal corneal thinning in keratoconic eyes. This method was at least as sensitive and specific as the topographic KISA. Financial Disclosure(s) Proprietary or commercial disclosure may be found after the references.