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Y. Li, O. Tan, M. Tang, D. Huang; Corneal Epithelial Thickness Mapping With Fourier-Domain Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2813.
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To map corneal epithelial thickness with optical coherence tomography (OCT).
A Fourier-domain OCT system (RTVue, Optovue Inc., Fremont, CA) with a corneal adaptor module (CAM) was used to image the cornea. It operated at 0.8 µm wavelength and had a scan rate of 26,000 axial-scan/second. The axial resolution was 5 µm in tissue. A pachymetry scan pattern (8 radials, 1024 axial scans each, 6mm diameter, repeat 3 times) centered at the corneal vertex was used to map the thickness of the cornea and its sub-layers. The three repeated scans in a scan set were registered and averaged before epithelial boundary detection. The epithelial thickness (tear film included) map was divided into 3 zones by diameter: central 2 mm, superior 2-5 mm, and inferior 2-5 mm. The average epithelial thickness value from each zone was calculated. 24 eyes of 12 normal subjects were scanned 4 times. The repeatability of the measurement was evaluated by the pooled standard deviation (SD).
The central, superior, and inferior epithelial thickness averages (± population SD) were 53.5 ± 2.4 µm, 49.4 ± 2.4 µm, 50.1 ± 2.5 µm. There was no significant differences between right and left eyes (T-test, p=0.69, 0.37, 0.31). The epithelium was thicker in the center than in the superior (mean difference 3.8 ± 1.3 µm, p<0.001) and inferior zones (3.2 ± 1.1 µm, p<0.001). The inferior epithelium was slightly thicker than the superior epithelium (mean difference 0.6 ± 1 µm, p<0.001). The repeatability of the measurements was 0.7 µm in all three zones.
High-resolution high-speed FD-OCT is able to map the corneal epithelial thickness with excellent reproducibility. The averaged epithelial thickness pattern is consistent with previous literature based on ultrahigh frequency ultrasound.
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