Project Summary/Abstract Human vision starts when photoreceptors collect and respond to light. Normal photoreceptor function is essential for normal vision, yet techniques to assess these processes in vivo are limited. New optical modalities that are rapid, specific, and non‐invasive promise to greatly expand our capability to monitor more accurately and completely photoreceptors. This study takes advantage of unique adaptive‐optics OCT instrumentation developed in my laboratory in conjunction with custom algorithms for sub‐cellular image registration and phase‐sensitive detection to measure anatomical and physiological properties of individual photoreceptors. We will use this technique to investigate three specific aims that quantify the spectral sensitivity profiles of photoreceptors, the expression of photoreceptor spectral types in color vision deficiencies, and the temporal dynamics of photoreceptor loss in retinitis pigmentosa patients. The long term goal of this research is to establish high resolution, high specificity optical techniques as valid tools for probing structure and physiologic processes of the retina at the cellular scale. The resulting ability to study cells in vivo will improve early detection of and treatment monitoring for diseases that impact the retina.