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A Pallikaris, DR Williams; Temporal Variation in the Reflectance of Single Cones in the Living Human Eye . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1969.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Adaptive optics allows the observation of single cone photoreceptors in the living human eye. In all eyes in which we have been able to image cones, there are large differences in the reflectance of different cones, even when all the photopigment is bleached. To help understand what produces this variation, we explored how the reflectance of cones changes over time. Methods: High-resolution, fully-bleached cone images were acquired in one eye using an adaptive optics system. We collected images over a 10 minute period approximately every hour for 24 hours. The subject followed his normal schedule during the day, though sleep was disrupted at night. A minimum of 3 images were registered and summed for each hourly sample. Images were acquired on two different days. To characterize rapid changes in reflectance, we also collected images in rapid succession within periods of several minutes. To quantify any variation in reflectance over time, we crosscorrelated pairs of images taken at different times and plotted the correlation as a function of the time between image acquisition. Results: The spatial variation of cone reflectance across the mosaic at any one time appears unsystematic. However, the reflectance of individual cones changes over time, causing the correlation between pairs of images to decrease continuously as a function of time elapsed between image acquisition out to at least 24 hours. In some cases, the reflectance of a cone can even change quite rapidly by as much as a factor of 2.4 within 10 minutes. Conclusions: The reflectance of individual cones is not a static property of the mosaic but changes over time. Large changes can be observed over periods of minutes as well as many hours. Previous work has shown that the spatial variation in reflectance is not related to variation in the optical axes of different cones. The demonstration of temporal variation here shows that a dynamic process is involved such as, conceivably, disc shedding.
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