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Conrad Merkle, Danielle J. Harper, Marco Augustin, Pablo Eugui, Bernhard Baumann; Identification of Melanin Migration Using Spectroscopic Optical Coherence Tomography at 840 nm. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2542.
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© ARVO (1962-2015); The Authors (2016-present)
Migration of melanin into the inner retina may signal disruption of the retina and vision-threatening eye disease. Recent advances in optical coherence tomography (OCT) technology have enabled the identification of migrated melanin particles using polarization contrast. This potentially useful characterization is limited clinically by the available clinical OCT devices, which lack polarization contrast. Here we present a potentially clinically-viable method to identify melanin particles using spectral contrast at 840 nm and compare the results against coregistered polarization images.
A polarization-sensitive OCT ophthalmoscope with a 100 nm bandwidth at 840 nm was used to perform retinal imaging in the very-low-density-lipoprotein receptor (VLDLR) mouse model (N = 3, age 11 weeks). The VLDLR model produces severe retinal disruption from choroidal neovascularizations accompanied by melanin migration. In each mouse, volumetric scans with 5 B-scan repeats were performed. From each volume, both polarization and spectral information were extracted in post-processing. For spectral processing, the raw OCT data was split into a short-wavelength channel and a long-wavelength channel using Gaussian filtering. From each channel, standard OCT structural images were reconstructed (Figure 1A-B). Finally, a spectral ratio image was generated by dividing the long-wavelength image by the short-wavelength image (Figure 1C-D). Polarization information was used to generate retardation images using standard processing methods.
The spectral ratio processing clearly identifies regions of the retina with non-uniform spectral profiles, such as migrated melanin particles and the retinal pigment epithelium (Figure 1C-D). Spectral ratio hotspots between the outer plexiform layer and the retinal pigment epithelium are similarly identified as depolarizing structures in the retardation images (Figure 2). The strong agreement between the two methods supports the hypothesis that these new spectral ratio measurements can identify inner-retinal melanin migration without polarization information.
The spectral ratio imaging demonstrated here at 840 nm enables melanin identification through software, rather than hardware. This new method can be applied to currently-used, commercially-available clinical OCT systems. This might directly improve clinical ophthalmology without requiring costly new hardware.
This is a 2020 ARVO Annual Meeting abstract.
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