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Hao F Zhang, Ji Yi, Siyu Chen, Xiao Shu, Amani A Fawzi; Optical coherence tomography using visible light on human subjects. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1667. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To date, all clinical OCT used near infrared (NIR) illumination. Though NIR enables deeper penetration into the tissue, it also comprise the ability to image absorption-related functional parameters. The applications include retinal oxygen metabolism, a key indicator of retinal health. We address the problem by developing a dual modality OCT/SLO system working in the visible-light spectral range, where hemoglobin molecule has peak absorption. It offers the potential of OCT oximetry in clinical human applications.
A supercontinuum laser provided illumination light ranged from 496 to 632 nm for both SLO and OCT. The OCT subsystem used free-space Michaelson configuration to avoid optical dispersion associated with fiber optics within spectral range. When operated in SLO mode, the system has one additional beam splitter inserted within the sample beam of the OCT. An avalanche photodiode detected the separated back-scattered light from retina. During imaging, the human subject rested on a chin rest mounted on a three-dimensional translational stage for alignment.
Fig. 1 shows the images from a healthy volunteer. In the SLO image, the fovea appeared as a central dark area, which is surrounded by hyper-reflectance of the macula. In both modalities, blood vessels can be clearly visualized. In the OCT B-scan image, a total of 12 retinal layers can be recognized. Especially, the nerve fiber layer (NFL) on the temporal side appeared thicker than that on the nasal side. In addition, the submicron axial resolution permitted us to distinctly resolve the Bruch’s membrane, which was usually merged with the RPE in NIR OCT.Fig. 2 shows the images from around the optic nerve head (ONH). Both SLO and OCT revealed vascular pattern of the same area. In the magnified views, the finer features in the lamina cribrosa were clearly observable. In OCT image, we could also observe the fibrous texture of the NFL. The OCT cross-section showed thickening of the NFL around the ONH, while the detailed scattering textures within the layer was also visible.
We demonstrated the first dual-modality human OCT/SLO system within the visible spectral range. Both modalities offered qualities comparable to existing clinical systems. In addition, visible light provided improved sub-micrometer axial resolution for greater anatomical details.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Fig. 1 SLO and OCT images around the fovea.
Fig. 2 SLO and OCT images around the optical nerve head.
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