A method for non-invasive assessment of photoreceptor function in a mammalian subject comprises exposing a subject's eye to a visible light stimulus to initiate an intrinsic reflectance response in one or a population of photoreceptors and capturing multiple images of photoreceptor's intrinsic reflectance response to the stimulus. Patterns of variability in the intrinsic reflectance response of a single photoreceptor or population of photoreceptors are useful in diagnosis and treatment monitoring of an ocular condition, disease, disorder or a response to treatment for said ocular condition, disease or disorder.