Characterization of outer retinal morphology with high-speed, ultrahigh-resolution optical coherence tomography

Purpose. To visualize, quantitatively assess, and interpret outer retinal morphology by using high-speed, ultrahigh-resolution (UHR) OCT. Methods. Retinal imaging was performed in the ophthalmic clinic in a cross-section of 43 normal subjects with a 3.5-μm, axial-resolution, high-speed, UHR OCT prototype instrument, using a radial scan pattern (24 images, 1500 axial scans). Outer retinal layers were automatically segmented and measured. High-definition imaging was performed with a 2.8-μm axial- resolution, high-speed, UHR OCT research prototype instrument, to visualize the finer features in the outer retina. Results. Quantitative maps of outer retinal layers showed clear differences between the cone-dominated fovea and the rod- dominated parafovea and perifovea, indicating that photoreceptor morphology can explain the appearance of the outer retina in high-speed, UHR OCT images. Finer, scattering bands were visualized in the outer retina using high-definition imaging and were interpreted by comparison to known anatomy. Conclusions. High-speed UHR OCT enables quantification of scattering layers in the outer retina. An interpretation of these features is presented and supported by quantitative measurements in normal subjects and comparison with known anatomy. The thick scattering region of the outer retina previously attributed to the retinal pigment epithelium (RPE) is shown to consist of distinct scattering bands corresponding to the photoreceptor outer segment tips, RPE, and Bruch,s membrane. These results may advance understanding of the outer retinal appearance in OCT images. The normative measurements may also aid in future investigations of outer retinal changes in age-related macular degeneration and other diseases.