Thickness Mapping of Photoreceptors of the Foveal Region in Normals Using Three–Dimensional Optical Coherence Tomography

Abstract

Abstract: : Purpose: To quantitatively determine two–dimensional thickness maps of the inner and outer segments of the photoreceptor (PR) layer in normals from three–dimensional ultrahigh resolution optical coherence tomography (3D UHR–OCT). Methods: 20 eyes of healthy young volunteers were imaged using a second generation ultrahigh resolution OCT system for three–dimensional video–rate retinal imaging employing a compact, commercially available ultrabroad bandwidth (160 nm) Titanium:saphire laser. Three dimensional retinal imaging can be performed with high axial resolution of 3µm and up to 25 B–scans/second, each tomogram consisting of 1024x1024 pixels, resulting in 25 Megavoxels/second. Results: 3D UHR–OCT images all major intraretinal layers of the eye. The junction of the inner/outer photoreceptor layer and the external limiting membrane are clearly visualized. The thickness of the PR varies from 50 µm (range: 46–57 µm) parafoveally to 90 µm (range: 85–95 µm) in the foveal region, consistent with the well–known increase in length of the outer cone segment from 22 µm (range: 20–27 µm) parafoveally to 35 µm (range: 33–38 µm) in the center of the fovea, where the length of the inner and outer photoreceptor segments are approximately equally distributed. Conclusions: 3D UHR OCT imaging allows visualization of all major retinal layers, including the photoreceptor inner and outer segment. Since the PR is affected in most retinal diseases, 3D UHR–OCT could become a useful tool for early diagnosis and monitoring the post–operative course. Quantitative PR thickness maps will be used as a normative database for future clinical studies using 3D UHR–OCT.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina • macula/fovea