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Michael Pircher, Julia S. Kroisamer, Franz Felberer, Harald Sattmann, Erich Götzinger, Christoph K. Hitzenberger; Renewal Process of Human Cone Outer Segments Observed In Vivo with SLO/OCT. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2663.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate long term temporal changes of human cone photoreceptors that may be associated with the renewal process of cone outer segments with the use of transverse scanning (TS) optical coherence tomography (OCT).
In this study a TS OCT/SLO instrument operating at a frame rate of 40 fps (transverse frames, imaging area ~300 x 300µm2) is used that records SLO and OCT images simultaneously. In both imaging modalities the cone mosaic can be observed in healthy volunteers down to an eccentricity of 2° from the fovea. The SLO images are used in a post-processing step to correct for transverse eye motion. Together with an incorporated axial eye tracker the instrument provides nearly motion artifact free 3D data of the retina. Exactly the same location on the retina (~4° nasal to the fovea) is measured over different extended time periods (hours up to several days). The 3D data sets are aligned to each other in all 3 dimensions which enables the observation of temporal changes of single cone photoreceptors.
Within 8 hours, apart from intensity fluctuations (within the junction between inner and outer segments of cones (IS/OS), end tips of photoreceptors (ETPR) and retinal pigment epithelium (RPE)) no changes in the depth position of the reflection sites of the cones could be observed. However, changes in the depth position of the ETPR are visible within 96 hours. Moreover, bright reflection spots (BRS) which can be observed within the cone outer segments in ~4% to 8 % of the cones show motion towards the end tips of the cones. The motion speed of the bright reflection spots was measured in two healthy volunteers with 110nm per hour which corresponds to cone outer segment renewal rates observed in animal studies.
This study investigates the 3 dimensional structure of individual cone photoreceptors over extended time periods. The observed BRS may originate from defects within the packing of cone outer segment discs. We hypothesize that the observed motion of these BRS within 96 hours is caused by the process of cone outer segment renewal. New discs are generated at the IS/OS while older discs are shed by the RPE at the location of the ETPR which leads to a motion of the BRS towards the ETPR. The varying depth positions of the ETPR may be explained by a different status within the disc shedding process.
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