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Elaine Wells-Gray, Stacey S Choi, Nathan Doble; Volumetric imaging of retinal ganglion cells and inner retinal microstructure using a combined AO-OCT-SLO. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4607.
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Adaptive optics-optical coherence tomography (AO-OCT) is a high-resolution imaging modality capable of revealing cellular-level details of the retina in three dimensions (3D). Visualization of weakly scattering cells in the inner retina requires averaging many 3D image volumes precisely registered to correct for eye motion. The aim of this work was to develop an AO-scanning laser ophthalmoscopy (SLO)-based eye motion tracking AO-OCT 3D registration method and to assess its use in multi-volume averaging of 3D retinal image data in normal subjects and those with glaucoma.
A combined AO-OCT-SLO imaging system acquired simultaneous AO-OCT B-scans and AO-SLO-frames at 60 Hz. Eye motion was quantified in post-processing from AO-SLO frames and use to render AO-OCT B-scan data in to 3D volumes. More than 40 volumes were averaged (per subject) in order to increase the signal-to-noise ratio in the resulting images. Inner retinal microstructure was examined in two-dimensional en face and B-scan projections of the 3D averaged data from two control subjects with normal vision and two subjects with primary open angle glaucoma (POAG).
Retinal ganglion cells (RGCs) could be resolved in the both the en face and B-scan projections in control subject 1 (5° and 10° temporal [T]) and POAG subject 1 (3°T-3° inferior [I]). Average transverse soma diameters were 10.4 µm (5° T, control), 15.8 µm (10° T, control), and 15.0 µm (3°T-3°I, POAG), respectively. In control subject 2 (5° T) and POAG subject 2 (7° S), RGC layers were observed in B-scan projections, but only partially resolved in the en face plane, such that RGC size could not be reliably measured. In both POAG subjects, the thickness of the RGC layer was reduced at locations with visual field loss as compared to the same location in the control eye. (72% and 34%, POAG subjects 1 and 2, respectively). SNR increased with number of volumes averaged, with the greatest increase (2.1 dB from 5° T data from control subject 1) between N=2 and N=10 volumes.
En face eye motion tracking through registration of AO-SLO images is a viable approach for 3D rendering and averaging of 3D AO-OCT data, which can reveal cellular microstructure of the inner retina. More work is needed to identify and mitigate the factors limiting the precision of en face image registration.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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