The present disclosure provides systems and methods for objective focal length free measurements of fluid flow using OCT. In certain disclosed examples, fOCT data is acquired and optical information is extracted from fOCT scans to quantitatively determine a flow rate of fluid in the target. Determinations of flow rate can enable determination of a change in rate of an analyte over time. The current methods and systems of the disclosure can be used in assessing metabolism of a tissue, where oxygen is the analyte detected, or other functional states, and, more generally, be used for the diagnosis, monitoring and treatment of disease.
