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Ramkumar Sabesan, Vimal Prabhu Pandiyan, Xiaoyun Jiang, James A Kuchenbecker, Maureen Neitz, Jay Neitz; Cone spectral classification with adaptive optics line-field OCT. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1127.
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© ARVO (1962-2015); The Authors (2016-present)
Adaptive optics (AO) line-field OCT can visualize stimulus-induced retinal activity in individual cones, characterized as a fast contraction followed by a slow expansion in outer segment optical path length(OPL). Here we investigate the feasibility of this wavelength-dependent optical signature to delineate cone spectral types and compare it against AO retinal densitometry.
An AO line-field OCT was used to image the cone mosaic at 1.5 to 5 deg temporal ecc. after 3 min. dark adaptation. The B-scan rate was 6 to 16.2 kHz and field of view was 0.8 to 1.5 deg. OCT volumes were recorded after a 660 nm or 528 nm, 5-10 ms LED flash. OPL was computed between individual cone inner/outer segment junction and outer segment tips in registered and segmented volumes to yield a measure of light-induced activity. In addition, a multi-wavelength AO scanning laser ophthalmoscope (SLO) was used for spectral typing via absorption imaging of the cone mosaic (1.5 deg. temporal ecc.) at 550 nm (S vs. LM cones) and 578 nm (L vs. M cones), following 5 min. dark adaptation. The change in OPL in OCT and the change in image intensity in SLO was subjected to Gaussian mixture model clustering analysis.
Cone types were readily delineated via both techniques across all eccentricities. In absorption imaging, the optical density of cones – 0.41±0.14 and 0.30±0.14 log units at 550 nm and 578 nm respectively – defines the measurable limits for differential LMS-cone pigment concentration. OPL changes arising from OCT, on the other hand, have greater sensitivity by ~2.5 log units (~300-fold), since the underlying mechanism is tied to the pigment action spectra and the amplification kinetics of phototransduction. With densitometry, the error rates and probabilities of cone assignments followed published literature, while OCT significantly outperformed it in both aspects. In OCT, the differential increase in cone outer segment OPL following 660nm stimulus was used to separate the 3 cone types (L,M,S-cones: 270 nm,90 nm,0 nm on average respectively). The early contraction amplitude after 528 nm stimulus was used in addition to confirm putative S-cones against L and M-cones (43 nm in LM-cones and <5 nm in S-cones on average).
Stimulus-induced changes in phase offer several significant advantages over change in intensity as an optical signature to identify cone spectral types, and probe photopigment characteristics in general.
This is a 2020 ARVO Annual Meeting abstract.
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