Abstract: A non-invasive spectral measurement of a native, diagnostic or treatment component in blood or tissue, illuminates the back of the eye and collects return light that has passed through and been reflected from choroidal or retinal tissue. Spectral analysis detects a retinal tissue state, or detects the level of a blood or serum constituent, which may be a native constituent or a dye, marker or pharmacological agent. Time-resolved or spectral decay monitoring may be used to assess organ functioning, e.g., by administering a serum-carried indicator of uptake, clearance or binding rate for specific organs. Circulating cells or material diagnostic of different conditions may also be detected by spectral analysis, either directly, or by tagging with a suitable label.