The importance for vision of the tiny fovea has been established by centuries of investigation as well as observations of the devastating consequences of its damage through injury or disease. Though evidence suggests that the fovea contains the full complement of the two dozen or so classes of ganglion cells found in peripheral retina, we know little about the physiology of these foveal cells. This gap in our understanding is the result of challenges in obtaining electrophysiological recordings from this delicate and topographically-complex structure. These challenges have been overcome by a method developed in our laboratory that allows simultaneous calcium imaging of the fluorescence responses of hundreds of foveal retinal ganglion cells in response to visual stimuli. Because this technique allows recording from single cells without damage in the living eye, we can study the same cells for months or even years, offering the opportunity to characterize the performance of each cell more thoroughly than has been possible with any prior method. Since the first submission of the proposal, we have made significant improvements in the expression of calcium indicator, GCamMP6s, in ganglion cells that increases the extent of expression to greater eccentricities, the fluorescence signal from each cell, as well as reducing the loss of ganglion cells over time. Moreover, we have designed a new ophthalmoscope with two independent adaptive optics systems, one dedicated to high resolution stimulus delivery and a second dedicated to high resolution ganglion cell recording. We have also developed an extensive battery of visual stimuli to characterize the responses of each cell in space, time, and color. This battery will include a white noise stimulus capable of identifying the locations and classes of single cone inputs to the receptive fields of foveal ganglion cells. To assist in cell classification, these physiological observations will be supplemented with ex vivo and in vivo histological analysis of the morphology of ganglion cell dendritic arbors. Armed with these improvements, we will undertake a comprehensive survey of both the physiology and anatomy of the foveal ganglion cell classes that mediate primate foveal vision.
Human vision is best at the fovea, yet we know much less about the specific code that the retina uses to convey the retinal image to the brain than we do about peripheral retina. This project will use a new technological approach to survey the different kinds of retinal cells that provide us with vision at the fovea, knowledge that could accelerate the development of new approaches to restoring vision in the blind.
