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Yichao Li, Robert N Fariss, Ethan D Cohen, Haohua Qian; Light-induced thickening of photoreceptor outer segment layer detected by ultra-high resolution OCT imaging. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1307.
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© ARVO (1962-2015); The Authors (2016-present)
There has been an increasing usage of OCT imaging for functional measurements of retinal activity due to its non-invasive property. In this study, we investigated light-induced changes in the retinal thickness using ultra-high resolution OCT imaging methods.
C57BL/6J mice at 4-months of age were used in this study. Dark-adapted animals were prepared under dim red light and imaged in a dark room, whereas light-adapted mice were imaged under room light (200 lux). Measurements were made at the same time of the day to avoid any possible circadian rhythm-related changes. A Bioptigen UHR system (1.6 µm/pixel axial resolution) with EDI mode was used to capture the OCT images. Data analysis was performed in Diver 2.4 (Bioptigen, Inc.) and ImageJ.
OCT images obtained from mice in room light exhibit a prominent dark band between the RPE and photoreceptor (PR) tip layers when compared with those obtained from the same eyes after over-night dark-adaptation. The whole retina thickness of light-adapted eyes is 6.8+0.7 µm longer than those measured under dark-adapted conditions (n=13). This difference is mainly manifested at the PR outer segments (OS), with no significant changes in either inner retinal thicknesses or PR inner segment length. Preliminary results from histological analysis revealed a similar change in OS length, indicating a good correlation between the optical measurement with OCT image and the physical distance of retinal tissue observed histologically. Elongation of OS can be detected even with brief light exposure, changes of 2.0+0.4 µm after 15 min of light (n=3), and 4.1+1.0 µm after 2hr of light (n=6). Similarly, 2hr dark-adaptation leads to a shortening of 4.0+0.8 µm in OS length (n=7). After prolonged dark-adaptation, there was an elongation of OS when compared with over-night dark-adapted eyes, with changes of 2.4+1.0 µm for 8-day darkness (n=7) and 2.2+0.6 µm for 27-day darkness, respectively. These changes in prolonged darkness are consistent with photostasis mechanisms of rod PR.
Light-induced change in the OS length is shown as an extra dark band on OCT image. This is consistent with light-induced fluid accumulation under sub-retinal space. If confirmed, OCT images can be used as another non-invasive measure of retinal and RPE function.
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