High-speed adaptive optics functional imaging of cone photoreceptors at a 100 MHz pixel rate

We evaluate a novel non-invasive technique for observing fast physiological processes, such as phototransduction, in single photoreceptor cells in the living human eye. The method takes advantage of the interference of multiple reflections within the outer segments of cones. This self-interference phenomenon is highly sensitive to phase changes such as those caused by variations in refractive index and scatter within the photoreceptor cell. A high-speed flood-illumination retina camera equipped with adaptive optics (AO) is used to observe this interference pattern, and to monitor the changes in those patterns in response to visible stimuli. AO and high frame rates are necessary for resolving individual cones and their fast temporal dynamics, respectively. Preliminary results suggest that a frame rate of 192 fps, corresponding to a full field 1024x512 pixel rate of 100 MHz, may be sufficient for observing these early stages of phototransduction. This pixel rate is at least 80 and 10 times faster than current flood-illumination and SLO pixel rates, respectively. To our knowledge this is the first demonstration of in vivo single photoreceptor functional imaging, and the first demonstration of in vivo optical detection of phototransduction.