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Shau Poh Chong, Marcel Trerice Bernucci, Harsha RADHAKRISHNAN, Vivek Jay Srinivasan; Structural and functional human retinal imaging with a fiber-based visible light OCT ophthalmoscope. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3101.
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© ARVO (1962-2015); The Authors (2016-present)
While Optical Coherence Tomography (OCT) imaging at 800 nm and 1050 nm enables excellent tissue architectural contrast, visible light (450 – 700 nm) is more sensitive to absorption from chromophores such as photopigment, melanin, and hemoglobin, as well as scattering from subcellular structures, all of which are potential retinal disease biomarkers. The purpose of this study is to test the hypothesis that by 1) changing the wavelength range of OCT to the visible and 2) developing and validating spectroscopic and Doppler algorithms, reliable and consistent estimates of blood oxygenation, total hemoglobin concentration, and total blood flow in the human retina can be achieved.
A fiber-based visible-light spectral/Fourier domain OCT system was constructed for in vivo imaging of human retina. A higher repetition rate, lower noise, supercontinuum light source was found to enable a sensitivity of 96 dB with 0.15 mW light power at the cornea and a 98 microsecond exposure time. Using a broadband (560 ± 50 nm), 90/10, fused single-mode fiber coupler designed for visible wavelengths, the sample arm was integrated into an ophthalmoscope platform, similar to current clinical OCT systems.
High-resolution in vivo structural retinal imaging at < 2 micron axial resolution and with angular field-of-view of up to 40° was demonstrated at 0.15 mW exposure with 10,000 and 70,000 axial scans per second (the latter comparable to commercial OCT systems), and at 0.03 mW exposure and 10,000 axial scans per second (below maximum permissible continuous exposure levels). Lastly, in vivo spectroscopic imaging of anatomy, saturation, and hemoglobin content in the human retina are shown in the Figure.
Here we introduce, validate, and demonstrate methods for quantifying blood flow, oxygenation, and hemoglobin content in the inner retinal vessels with fiber-based visible light spectroscopic OCT. Applying Fick’s principle, these methods will enable oxygen metabolic imaging of the inner retina.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
(A) Image of Doppler velocities overlaid on structural OCT image. (B) Cumulative hemoglobin concentration in retinal vessels exhibits a characteristic downward “crescent” shape, due to a larger cumulative path length at the distal end of the vessel. (C) Oxygen saturation mapping in retinal vessels is shown, with a spectroscopic fit for the distal portion of a vein (D).
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