[Optical Doppler velocimetry of red blood cells at different depths in retinal vessels by varying the coherence length of the source: feasibility study].

Purpose: To report on a novel approach to measure the velocity of red blood cells (RBCs) at different retinal vessel depths.

Method: The technique is an extension of conventional laser Doppler velocimetry using light sources of various coherence lengths (CL). Light scattered by the moving RBCs interferes with that reflected from the anterior vessel wall only if the optical path difference is shorter than CL. Therefore, using low coherence light sources, localized measurements of RBCs velocity can be performed.

Results: Measurements of RBCs velocity at different depths in a main retinal vein (diameter: 152 microns) of a volunteer has been performed using 4 different light sources with CLs of 14 microns, 21 microns, 32 microns and > m. Measured values are in good agreement with theoretically predicted values.

Conclusion: This new approach permits to measure RBCs velocity at different depths of retinal vessels in the human retina.