Evaluation of the Repeatability and Reproducibility of Corneal Epithelial Thickness Mapping for a 9-mm Zone Using Optical Coherence Tomography

PURPOSE: To evaluate the repeatability and between-machine/operator reproducibility of optical coherence tomography (RTVue-XR) for mapping corneal epithelial thickness (ET) and corneal thickness (CT) over a 9-mm zone. METHODS: In 5 groups of eyes (normal, contact lens, dry eye, post-LASIK/PRK, and keratoconus), corneal ET and CT were evaluated in 25 areas in the following 4 regions: 1) 1 central zone within 0 to 2.0 mm diameter, 2) 8 paracentral zones from 2.0 to 5.0 mm diameter, 3) 8 midperipheral zones from 5.0 to 7.0 mm diameter, and 4) 8 peripheral zones from 7.0 to 9.0 mm diameter. Three devices with designated operators were used to obtain 3 scans per device for each eye. The repeatability, reproducibility, and coefficient of variation were calculated. RESULTS: For all areas up to 9 mm diameter, in normal eyes, contact lens eyes, dry eyes, post- LASIK/PRK eyes, and keratoconic eyes, repeatability and reproducibility ranged from 0.7 to 1.5, 1.0 to 2.6, 0.9 to 2.0, 0.7 to 2.5, and 1.1 to 2.3 μm for ET and 1.5 to 8.3, 2.3 to 12.1, 1.7 to 14.2, 1.4 to 13.7, and 6.9 to 18.9 μm for CT, respectively. The ranges of coefficient of variation values were 1.2% to 3.0%, 1.9% to 5.5%, 1.8% to 4.3%, 1.3% to 5.2%, and 2.2% to 4.5% for ET and 0.3% to 1.2%, 0.4% to 1.8%, 0.4% to 2.1%, 0.3% to 2.0%, and 1.2% to 3.0% for CT, respectively. CONCLUSIONS: Optical coherence tomography produced excellent repeatability and reproducibility for corneal ET and CT measurements up to a 9-mm zone in normal eyes and eyes with different corneal conditions. The CT measurements in keratoconic eyes were more variable than those in eyes with other corneal conditions.