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Furu Zhang, Zhuolin Liu, Kazuhiro Kurokawa, Donald T Miller; Diurnal Time Course of Cone Photoreceptor Disc Shedding in the Living Human Eye. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1265.
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© ARVO (1962-2015); The Authors (2016-present)
Photoreceptor outer segments (OS) undergo periodic shedding of small packets of membranous discs at their distal ends. This process, called disc shedding, is fundamental to maintaining health of the outer retina and believed to follow a diurnal rhythm. While disc shedding has been studied extensively in animal models, little is known in humans. In this study we took advantage of our recent discovery of the optical signature of disc shedding in the living human eye using adaptive optics-optical coherence tomography (AO-OCT)  to investigate the diurnal properties of this elusive event.
Two healthy subjects free of ocular disease were imaged at 3° temporal retina (1.5°×1.5° FOV) with the Indiana AO-OCT system. Subjects were entrained to a 16/8 hour awake/sleep cycle for three days preceding the experiment. On the day of the experiment, the subjects awoke 2 hours before the entrained wakeup time, and the experiment started 1 hour later. Volume videos were acquired every 15 minutes for 17 hours. One subject stayed under stable room light during the entire experiment, while the other was also exposed to three 10-minute intervals of natural light over the day. B-scan and average A-scan time traces of each tracked cone were generated with the post-processing method described by Kocaoglu et.al . Both time-trace presentations were used to detect disc shedding events as manifested by spatial (axial) and temporal changes in inner segment/outer segment junction and cone outer segment tip reflections. In one subject, the OS length of each cone at each time point was measured.
Thousands of cones were successfully imaged and tracked over the 17 hour period in both subjects. Shedding events were detected in 79.5% and 72.6% of the tracked cones. Similar to previous animal studies, shedding prevalence exhibited a diurnal rhythm. But unlike almost all other diurnal animal models studied, shedding peaked shortly after the entrained wakeup time. Consistent with this, traces of the average cone OS length across the 17 hours implied maximum shedding shortly after the entrained wakeup time. Distinct from these diurnal changes, a significant but transient increase in shedding followed exposure to natural light.
Human cone photoreceptor shedding exhibits a diurnal rhythm that peaks in the morning and is sensitive to natural light. Kocaoglu, et al. Biomed. Opt. Express 7.11 (2016): 4554-4568.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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