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Omer Pars Kocaoglu, Zhuolin Liu, Kazuhiro Kurokawa, Donald Thomas Miller; Imaging Photoreceptor Shedding in the Living Human Eye. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified.
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© ARVO (1962-2015); The Authors (2016-present)
Photoreceptor outer segments (OS) undergo a regular cycle of renewal and shedding of membranous discs. These fundamental processes maintain the health of the outer retina, thus are of significant clinical interest. While both have been extensively studied in animal models and postmortem eyes, little is known about them in the living eye, in particular human. Only recently has renewal been observed optically in the living human eye, but the complementary shedding event has proven more elusive. In this study, we present to the best of our knowledge the first observations of disc shedding in living human retina.
Two healthy subjects were entrained to a 16/8 hour awake/sleep (light/dark) cycle. Subsequent to entrainment, subjects were imaged with the Indiana adaptive optics optical coherence tomography (AO-OCT) system using two-camera mode at 500 KHz for three 90-minute sessions (morning, afternoon, and evening). The morning session was approximately 1.5 hr after the subject awoke. AO-OCT images captured the 3D reflectance profile of individual cone photoreceptors at 2° temporal to the fovea, and their profiles were tracked over time. Images were acquired every three minutes. Volume videos were registered to remove axial and lateral motion, and cones were identified in every time point to generate single-cone cross-sectional videos. The videos and their two-dimensional time-lapse images were used to detect shedding events based on the temporal and spatial behavior of the reflections at the inner segment / outer segment junction (IS/OS) and cone outer segment tip (COST).
While the IS/OS reflection remained relatively stable over the imaging sessions, the COST reflection of some cones underwent dramatic change. Specifically, the COST disappeared entirely in both the AO-OCT cross-sectional and time-lapse images, returning minutes later but displaced axially that resulted in a slightly shortened OS. Average time duration of the disappearance was 14.3±14 minutes, and average axial displacement of COST was 1.8±1.3 µm (6% of OS length). Prevalence of cones whose COST temporally disappeared was higher in the morning session (~11%) compared to the afternoon and evening sessions (~4%). Collectively, these dynamics of the COST reflection are consistent of disc shedding.
We demonstrate the first observation of photoreceptor disc shedding in the living eye and present early results of its temporal and spatial properties.
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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