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A.E. Elsner, A. Weber, M.C. Cheney, Q.Y. J. Smithwick, S.A. Burns; Depth–coded polarization imaging . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1136.
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Purpose:To study light scattering of retinal and subretinal tissues, examining the influence of plane of focus and polarization content on light return and contrast. To examine sources of polarization–retaining and multiply scattered light at best subjective focus. To improve imaging techniques despite defocus, long–range scatter, or other optical artifacts. Methods:Five subjects (3 females, 2 males) were imaged, paralyzing the accommodation of those 7 diopters was acquired, in 0.5 diopter steps from best subjective focus. At each focal plane, there were 40 images: 20 input polarizations, and a pair of images for the crossed and the parallel polarized detectors. Roughly 600 images were aligned for computations. The Fourier transform for the 20 input polarizations per plane reduced pixel noise. Computed images varying in polarization content were compared across focal planes, for a foveal–centered annulus with the inner diameter at 1 deg and outer diameter at 2 deg, and a peripheral 1 deg circle. Results:All subjects were able to select their best subjective focus at 780 nm. This focal plane was within the more posterior (deeper) half of those focal planes leading to a large light return, and also was within .5 diopter of the subjectively best confocal image for 4 of 5 subjects. For image types that reduce scattered light by polarization, e.g. the maximum of the parallel detector, the axial transfer function remained broad: half widths at half height > 2 diopters for both fovea and periphery. Reflective portions remained bright in many planes. The macular bow tie pattern was relatively stable over moderate defocus. The return of depolarized light dropped sharply at the plane of best subjective focus for some subjects, yet these depolarized light images better visualized deeper features than brighter images elsewhere, which often had long range scattering artifact such as tear film. Conclusions:Even with 780 nm and a dark–adatped eye, minimally single scattered light from the nerve fiber layer dominates retinal imaging, a problem for imaging diseased structures with graded indices or high degree of scatter. Conveniently for clinical use, defocus is likely a minor problem for birefringence.
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