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Kazuhiro Kurokawa, James A. Crowell, Furu Zhang, Zhuolin Liu, Donald Thomas Miller; Imaging retinal function with phase-sensitive adaptive optics optical coherence tomography. Invest. Ophthalmol. Vis. Sci. 2018;59(9):728. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Recent advances in adaptive optics optical coherence tomography (AO-OCT) have enabled cells across the full depth of the living human retina to be visualized. While this success promises improved detection, diagnosis, and treatment monitoring of retinal pathologies, the method is limited primarily to cell structure. A more complete description would include cell function. Here we advanced point-scanning AO-OCT to measure phase changes associated with cell physiology and tested it on five retinal layers: retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), cone outer segment tip (COST), and retinal pigment epithelium (RPE).
Volume videos were acquired of the same retinal patch at 12° temporal to the fovea using the Indiana AO-OCT system (790 nm center wavelength; 2.4x2.4x4.7 μm3 nominal resolution in tissue). The system operated at 20 volumes/s and 500K A-scans/s; residual eye motion was corrected by registering volumes in 3D. We computed the complex temporal autocorrelation of each sampled point in the retina using registered volumes of varying time interval and extracted correlation time constants of each retinal layer. The experiment was repeated with 520 nm flash stimulation of the retina to test for an excitatory response. Phase differences at the GC and cone layers were also examined as a potentially more sensitive metric of physiologic activity.
We successfully measured the correlation time constants of the five retinal layers with and without stimulation. Without stimulation, average values were 1.10 s (RNFL), 0.86 s (GCL), 1.23 s (IPL), 1.24 s (COST), and 0.72 s (RPE) with avg+/-std of 1.03+/-0.23 s. Variations in time constant between retinal layers were significant (ANOVA, p<0.05). Time constants were significantly affected by stimulation (p<0.05), except for COST and RPE. Sensitivity of the phase-difference measurements was 0.03 (averaged over cones) and 0.11 (averaged over GCL) radians. 0.03 radians (equal to 1.3 nm OS length change) was sufficient to detect elongation of cone OSs (~6.4 nm) using our weakest stimulation (1.2 µW illuminating 2°). Elongation was found to increase linearly with stimulus strength. 0.11 radians was insufficient to detect phase changes at GCL.
Phase-sensitive AO-OCT can detect physiologic activity of the retinal layers—including changes induced by light stimulation—in the living human eye.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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