Corneal epithelial thickness mapping by Fourier-domain optical coherence tomography in normal and keratoconic eyes.
OBJECTIVE
To map the corneal epithelial thickness with Fourier-domain optical coherence tomography (OCT) and to develop epithelial thickness-based variables for keratoconus detection.


METHODS
Cross-sectional observational study.


METHODS
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 map the corneal epithelial thickness automatically. Zonal epithelial thicknesses and 5 diagnostic variables, including minimum, superior-inferior (S-I), minimum-maximum (MIN-MAX), map standard deviation (MSD), and pattern standard deviation (PSD), were calculated. Repeatability of the measurements was assessed by the pooled standard deviation. The area under the receiver operating characteristic curve (AUC) was used to evaluate diagnostic accuracy.


METHODS
Descriptive statistics, repeatability, and AUC of the zonal epithelial thickness and diagnostic variables.


RESULTS
The central, superior, and inferior epithelial thickness averages were 52.3 ± 3.6 μm, 49.6 ± 3.5 μm, and 51.2 ± 3.4 μm in normal eyes and 51.9 ± 5.3 μm, 51.2 ± 4.2 μm, and 49.1 ± 4.3 μm in keratoconic eyes. Compared with normal eyes, keratoconic eyes had significantly lower inferior (P = 0.03) and minimum (P<0.0001) corneal epithelial thickness, greater S-I (P = 0.013), more negative MIN-MAX (P<0.0001), greater MSD (P<0.0001), and larger PSD (P<0.0001). The repeatability of the zonal average, minimum, S-I, and MIN-MAX epithelial thickness variables were between 0.7 and 1.9 μm. The repeatability of MSD was better than 0.4 μm. The repeatability of PSD was 0.02 or better. Among all epithelial thickness-based variables investigated, PSD provided the best diagnostic power (AUC = 1.00). Using an PSD 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 PSD variable.


BACKGROUND
Proprietary or commercial disclosure may be found after the references.
Center for Ophthalmic Optics and Lasers, Casey Eye Institute and Department of Ophthalmology, Oregon Health and Science University, Portland, Oregon 97239, USA. liyan@ohsu.edu
Yan
Y
Li
Ou
O
Tan
Robert
R
Brass
Jack L
JL
Weiss
David
D
Huang
D000328:Adult; D000368:Aged; D019540:Area Under Curve; D063171:Corneal Pachymetry; D003430:Cross-Sectional Studies; D019573:Epithelium, Corneal / Q000473:pathology*; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D012372:ROC Curve; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D041623:Tomography, Optical Coherence; D055815:Young Adult