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W. Gao, B. Cense, O. P. Kocaoglu, Q. Wang, R. S. Jonnal, S. Lee, D. T. Miller; Dependence of Cone Photoreceptor Directionality on Retinal Eccentricity Using Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6295.
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The directional component of the retinal reflection, also called the optical Stiles-Crawford effect (SCE), is a well known result of the waveguide property of photoreceptors. The retinal layers that contribute to this effect, however, have only recently been investigated directly with the optical sectioning capability of spectral-domain optical coherence tomography (SD-OCT) . Here, we expand on this earlier report by extending the analysis from a single retinal eccentricity (2o) to a range of eccentricities (foveal center to 5o). Improved data processing was also developed for more precise extraction of layer information.
A research-grade SD-OCT instrument was designed for the study, which used a superluminescent diode (c= 842 nm; Δ=50 nm) that illuminated the retina and provided 5µm axial resolution in retinal tissue. Beam size was 2 mm at the eye pupil. In the sample channel, the galvo-scanners were mounted on a computer-controlled XY translation stage that systematically moved the beam across the pupil with images acquired at intervals of 0.5 mm. Three healthy subjects were recruited with eye dilated. Images were captured at the fovea and retinal eccentricities between 1o and 5o at 1 degree intervals. The reflectance of each major retinal layer was fit to a five-parameter model composed of a constant bias and a Gaussian function with directional parameter. The fit was also applied to the total reflectance (sum of all layers).
Reflections of the inner/outer segment junction (IS/OS) and posterior tips of outer segment (POS) were found highly sensitive to beam entry position regardless of eccentricity. IS/OS was less directional than POS. Strongest directionality was reached at 3o. In contrast, the reflection from the retinal pigment epithelium showed little directionality. Directionality of the total reflectance was dominated by the IS/OS and POS contributions and consistent with that reported with conventional reflectometric techniques.
SD-OCT was successfully used to measure the retinal contributions to the optical SCE over an extended range of retinal locations.
 W. Gao et al., Opt. Express 16, 6486-6501 (2008)
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