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Omer P. Kocaoglu, Ravi S. Jonnal, Qiang Wang, Sangyeol Lee, Zhuolin Liu, Donald T. Miller; Imaging The Living Human Cone Outer Segment: Temporal Dynamics In Reflectance And Length. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4649. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Cone photoreceptors undergo significant physiological and structural changes caused by the processes of disc renewal and shedding, biomolecule synthesis, and metabolic regulation. These processes are fundamental to the maintenance of phototransduction, yet little is known about their impact on the cone optical signature, in particular the strong reflections from the inner segment/outer segment junction (IS/OS) and posterior OS tip (PTOS). Using adaptive optics with optical coherence tomography (AO-OCT), we investigate the dynamics of these reflections and their separation (OS length) measured over hours and days.
This study used the Indiana AO-OCT system, which has been previously described. For this study, the OCT portion was configured with an Integral Femtolaser light source and a high-speed CMOS linescan detector that acquired retinal images at 167K A-scans/s. The AO was a woofer-tweeter system that dynamically compensated for ocular aberrations and optimized focus of the cones. Volume videos (0.65°x0.65°) were acquired at a rate of four per second at 1.5° temporal to the fovea with 3x3x3 μm3 resolution. On the same subject, volumes were acquired over two hours with 15 min intervals and over ten days with two to three day interval. Volumes were registered to remove motion artifacts, and individual cones were identified and tracked across the registered videos. Reflectance and axial separation of the IS/OS and PTOS were extracted from the volumes and changes computed.
20 cones were successfully tracked over two hours and 10 over 10 days. Over hours, the average root-mean-square (RMS) change in reflectance of the IS/OS and PTOS was 17% and 19%, respectively, measured from normalized intensity traces of all 20 cones. Over days, the average RMS was similar,17% and 18%, respectively. Average peak-to-valley changes were 45% and 48% (hours) and 44% and 43% (days). For the cone OS length, no detectable change was observed over hours. That is, changes were smaller than the 1.4 µm sensitivity of the AO-OCT system for single cone measurements. Over days, a slight but significant change was observed (1.6 μm average RMS).
IS/OS and PTOS reflections exhibit significant fluctuations across hours and days. Changes in OS length are observed over days, but not hours.
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