Choroidal blood flow in the foveal region of the human ocular fundus.

PURPOSE To develop a noninvasive method for the investigation of choroidal blood flow (ChBF) and its regulation in the foveal region of the human ocular fundus. METHODS Measurement of ChBF was based on the technique of laser Doppler flowmetry (LDF). Sixteen normal subjects (age range, 20 to 64 years), with normal eye examination results, were asked to fixate on a diode laser beam (wavelength = 811 nm, 60 microW at the cornea) delivered to the undilated eye through a fundus camera. Light scattered by red blood cells in the tissue volume sampled by the incident laser beam was detected at the fundus image plane of the camera by an optical fiber. The diameter of the beam at the fundus of the emmetropic eye was about 300 microns. Relative ChBF was measured in both eyes by analyzing the Doppler signal with commercial skin blood flowmeters. The average pulsatile component of ChBF, ChBFP, was determined over the cardiac cycle, and its value was compared to the average total ChBF, ChBFAV. Responses of ChBF to various physiological stimuli, such as increased blood O2 and CO2 concentrations, rapid increases in intraocular pressure, and valsalva maneuvers, were documented. RESULTS Significant correlations were obtained between the ChBFAV values measured with both flowmeters (P < 0.001) and between the ChBFAV values measured in the right and left eye (P < 0.001). ChBFP represented less than 23% of ChBFAV. ChBFAV was not significantly affected by 5 minutes of breathing 100% oxygen. Raising end-tidal CO2 in one subject from 37 to 59 mm Hg increased ChBFAV by approximately 40%. Acute elevation of the intraocular pressure by suction cup or finger pressure on the globe reduced ChBFAV by as much as 90%. Valsalva maneuvers induced reproducible responses that were very different from those recorded from the skin microcirculation. CONCLUSIONS Although LDF of the choroidal circulation is still at an early stage of development, this noninvasive method appears to provide continuous and sensitive measurements of relative choroidal blood flow in the foveal region of the human fundus. Near-infrared laser diodes enable measurements through undilated pupils. Examples of responses suggest new avenues in the investigation by LDF of the effect of various physiological stimuli, pharmacologic agents, and pathologic processes on the choroidal circulation in man.