The reflectance of single cones in the living human eye.

PURPOSE Individual cones were imaged in the living human eye with the Rochester adaptive optics ophthalmoscope. In all eyes, there were large differences in the reflectance of different cones, even when all the photopigment was bleached. To help understand what produces this spatial variation, the investigators explored whether it is a static or a dynamic property of the cone mosaic. METHODS Fully bleached cone images were acquired in three eyes with an adaptive optics system. Images were collected over a 10-minute period approximately every hour for 24 hours. The temporal variation in cone directionality was measured in one eye. Finally, the experimental data on the temporal variation of absorption were compared with findings in various models of reflectance. RESULTS Cone reflectance changes over time appear to be independent from cone to cone. These temporal changes are present in all three cone classes. The spatiotemporal variation in cone reflectance is not caused by the spatiotemporal variation in the optical axes of cones. This, along with the modeling results, suggest that changes in the reflectance affect the light that passes through photopigment in the receptors rather than the stray light, and that the changes are related to the outer segment-retinal pigment epithelium (RPE) interface. CONCLUSIONS The reflectance of individual cones is a dynamic property of the mosaic. Changes can be observed over periods of minutes as well as many hours. The cause of the variation is not known but may be related to the process of disc shedding in receptors.