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Brian Vohnsen, Salihah Qaysi, Pedro Anjos, Denise Valente; Exploring photoreceptor directionality using quadrant pupil detection. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4118. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Photoreceptors are endowed with directional properties that are expressed by their angular sensitivity to incident light and directionality in retinal imaging known as the Stiles-Crawford effect of the first kind (SCE) and the optical SCE, respectively. Individual photoreceptor tilt can be analyzed by moving the incident light across the pupil when capturing retinal images. The purpose of this study is to examine with numerical analysis and fundus imaging the viability of an alternative quadrant detection scheme in which retinal images are captured through four equal-sized pupil sectors from which individual cone photoreceptor tilts can be derived.
A numerical analysis has been performed for directional light scattering from photoreceptor cones in the retinal mosaic modeled as tri-layered structures that represent the location of mitochondria in the ellipsoid, the inner-outer segment junction and the posterior outer segment tip [Vohnsen, Frontiers in Optics (2014) FW5F.5]. Each outer segment has been added random tilt of varying amplitude. Simulated cone mosaic images are calculated through 4 equal-sized sectors in the pupil plane. The numerical predictions are compared with experimental quadrant parafoveal fundus images for healthy subjects.
The sectored quadrant pupil allows not only determination of total intensity images but also direct determination of local cone photoreceptor tilts (which may differ from their psychophysically relevant tilts) in two orthogonal directions using the sectored backscattered light intensity. It is found that the method is highly suited to determine tilt without requiring displacement of the incident light in the pupil plane whereby the analysis becomes simplified although it requires proper centration with respect to the SCE peak location. Retinal images in the healthy subjects show only small photoreceptor tilts in the parafoveal region but confirm the potential of the technique.
The numerical analysis shows that the quadrant pupil detection is suitable for rapid detection of individual photoreceptor tilts in the photoreceptor mosaic of less than 1 degree. With proper optimization this may have clinical potential for analysing perturbations caused by drusen and retinal disease that may alter the pointing of the photoreceptors causing a resulting deterioration of vision.
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