Abstract
.Optical coherence tomography (OCT) is a powerful tool in ophthalmology that provides in vivo morphology of the retinal layers and their light scattering properties. The directional (angular) reflectivity of the retinal layers was investigated with focus on the scattering from retinal pigment epithelium (RPE). The directional scattering of the RPE was studied in three mice strains with three distinct melanin concentrations: albino (BALB/c), agouti (129S1/SvlmJ), and strongly pigmented (C57BL/6J). The backscattering signal strength was measured with a directional OCT system in which the pupil entry position of the narrow OCT beam can be varied across the dilated pupil of the eyes of the mice. The directional reflectivity of other retinal melanin-free layers, including the internal and external limiting membranes, and Bruch’s membrane (albinos) were also measured and compared between the strains. The intensity of light backscattered from these layers was found highly sensitive to the angle of illumination, whereas the inner/outer segment (IS/OS) junctions showed a reduced sensitivity. The reflections from the RPE are largely insensitive in highly pigmented mice. The differences in directional scattering between strains shows that directionality decreases with an increase in melanin concentrations in RPE, suggesting increasing contribution of Mie scattering by melanosomes.
Highlights
Over the past several years, optical coherence tomography (OCT) has evolved into a powerful tool for the in vivo investigation of cross-sectional retinal anatomy and pathology.[1,2] OCT extracts depth-resolved information about the intensity of backscattered light from retinal layers using low coherence interferometry
We show that the magnitude and directional scattering from the retinal pigment epithelium (RPE) measured with a directional OCT (dOCT) correlates with the melanin concentration in the RPE, and can potentially serve as an indicator of pigmentation level in RPE cells
The directional reflectivities of the major scattering layers in retinas of mice with different melanin concentration levels were investigated with a dOCT system
Summary
Over the past several years, optical coherence tomography (OCT) has evolved into a powerful tool for the in vivo investigation of cross-sectional retinal anatomy and pathology.[1,2] OCT extracts depth-resolved information about the intensity of backscattered light from retinal layers using low coherence interferometry. Measuring changes in the angular (directional) scattering of retina layers might further enhance our ability to sense microscopic changes in cellular and subcellular morphology that might precede and/ or follow disease progression. This information is not utilized in current clinical OCT systems. Directional OCT (dOCT) imaging of human retina enables the delineation of HFL from the ONL and accurate measurement of macular photoreceptor nuclear layer thickness, which are important biomarkers for retinal degenerations.[7,8] The directional reflectance property shown by the photoreceptor bands, known as the optical Stiles–Crawford effect (SCE), provides the information on the structural integrity of the photoreceptors. An OCT-based assessment of the reflectivity of the photoreceptors layer is reported to study SCE in human retina.[9]
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