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Ravi Sankar Jonnal, Iwona M Gorczynska, John S Werner; Locating the rod IS/OS using AO-OCT. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4641. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
While rods have been imaged successfully using areal adaptive optics (AO) imaging1, 3D imaging of the rods is of interest because little is known about their contribution to the OCT B-scan, despite rods outnumbering cones by a factor of 10. Rods are known to be lost in the aging retina and AMD, and this loss may be better understood with the ability to examine their 3D morphology. Here we use AO-OCT to investigate rods in 3D, in particular the axial locus of the rod inner/outer segment junction (RIS/ROS).
Volumetric AO-OCT images subtending 1 deg were acquired from three healthy subjects, at eccentricities between 4 and 8 deg, where cone and rod outer segment tips (COST and ROST, respectively) are axially removed. Focus of the AO system was set by the en face visibility of the cone IS/OS mosaic. The AO correction provided diffraction-limited imaging, sufficient for resolving the complete cone mosaic at all eccentricities. Layers containing the cone IS/OS, COST, and ROST were automatically identified and segmented. Radially averaged power spectra and transverse correlation with ROST were computed at all depths in the volume.
In all subjects, en face views of cone IS/OS and COST showed patterns of reflectance consistent with the cone mosaic. En face views of ROST showed dark regions transversely co-located with cones, surrounded by brighter objects that may be individual rod outer segment tips. Radially averaged power spectra of IS/OS, COST, and ROST revealed peaks consistent with known spacings. Correlation of ROST with other layers revealed a significant peak between 5 and 10 μm distal to the cone IS/OS. In spite of this high correlation, a ROST-like mosaic was not visually apparent.
The observed correlation suggests that RIS/ROS is distally displaced from the cone IS/OS. This hypothesis is consistent with post-mortem light microscopy2 but inconsistent with the proximally-shifted focus required to visualize rods with AO-SLO1. The low reflectivity of RIS/ROS suggests that its optical properties are different from the cone IS/OS, and that 2D AO images of rods may be dominated by photons reflected by ROST.1. Dubra A, Sulai Y, Norris J, et al. Biomedical Optics Express. 2011;2(7):1864-1876.2. Fine BS, Zimmerman LE. Investigative Ophthalmology & Visual Science. 1963;2(5):446-459.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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