Elsevier

Ophthalmology

Volume 119, Issue 12, December 2012, Pages 2425-2433
Ophthalmology

Original article
Corneal Epithelial Thickness Mapping by Fourier-Domain Optical Coherence Tomography in Normal and Keratoconic Eyes

Presented in part at: American Society of Cataract and Refractive Surgery Annual Meeting, April 2010, Boston, Massachusetts; and Association for Research in Vision and Ophthalmology Annual Meeting, May 2010, Fort Lauderdale, Florida.
https://doi.org/10.1016/j.ophtha.2012.06.023Get rights and content

Objective

To map the corneal epithelial thickness with Fourier-domain optical coherence tomography (OCT) and to 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 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.

Main Outcome Measures

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.

Financial Disclosure(s)

Proprietary or commercial disclosure may be found after the references.

Section snippets

Patients

Subjects of this cross-sectional observational study were recruited at Doheny Eye Institute at the University of Southern California, Los Angeles, California; Brass Eye Center, Latham, New York; Gordon & Weiss Vision Institute, San Diego, California; and the Casey Eye Institute at Oregon Health and Science University, Portland, Oregon. This study followed the tenets of the Declaration of Helsinki and was in accord with the Health Insurance Portability and Accountability Act of 1996. The study

Results

Visual inspection confirmed that anterior corneal and epithelial boundary detection was satisfactory in 432 of 435 normal scans (99.3%) and in 107 of 114 keratoconic scans (93.9%). Three scans of normal eyes and 7 scans of keratoconic eyes were excluded from statistical analysis because of errors in boundary detection. Because the scans with segmentation errors occurred in different normal eyes, neither of those eyes was excluded. The keratoconic boundary detection errors resulted in the loss

Discussion

Fourier-domain OCT instruments can provide scan speeds 10 to 100 times faster than time-domain OCT instruments.26 The enhanced speeds minimize the effect of eye movements during data acquisition and also allow higher definition imaging because of denser axial scans in the same transverse scan length. The higher scan speed also facilitates frame averaging that suppresses speckle noise. The epithelium–Bowman's layer boundary is a relatively weak interface presented in corneal OCT images. In this

Acknowledgment

The authors thank Dr. Qienyuan Zhou for coordinating study data collection, Dr. Xinbo Zhang for consultation in statistics, and Dr. Maolong Tang for consultation on corneal topography.

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    Manuscript no. 2011-1777.

    Financial Disclosure(s): The author(s) have made the following disclosure(s): Yan Li received travel support, research grant support, patent royalty from Optovue, Inc., Fremont, CA; Ou Tan received research grant support, patent royalty from Optovue, Inc.; Robert Brass receives speaker honoraria from Optovue, Inc.; David Huang received stock options, patent royalty, travel support and research grant support from Optovue, Inc. David Huang receives royalties from the Massachusetts Institute of Technology derived from an optical coherence tomography patent licensed to Carl Zeiss Meditec, Inc. (Dublin, CA).

    These potential conflicts of interest have been reviewed and managed by Oregon Health and Science University.

    Supported by the National Institutes of Health, Bethesda, Maryland (grant no.: R01EY018184); a research grant from Optovue, Inc., Fremont, California; and an unrestricted grant to Casey Eye Institute from Research to Prevent Blindness, Inc., New York, New York.

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