CHOROIDAL BLOOD-FLOW IN THE FOVEAL REGION OF THE HUMAN OCULAR FUNDUS

Purpose. To develop a noninvasive method for the investigation of chor oidal blood flow (ChBF) and its regulation in the foveal region of the human ocular fundus. Methods. Measurement of ChBF was based on the te chnique of laser Doppler flowmetry (LDF). Sixteen normal subjects (age range, 20 to 64 years), with normal eye examination results, were ask ed to fixate on a diode laser beam (wavelength = 811 nm, 60 mu W at th e corneal delivered to the undilated eye through a fundus camera. Ligh t scattered by red blood cells in the tissue volume sampled by the inc ident 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 emm etropic eye was about 300 mu m. Relative ChBF was measured in both eye s by analyzing the Doppler signal with commercial skin blood flowmeter s. The average pulsatile component of ChBF, ChBF(P), was determined ov er the cardiac cycle, and its value was compared to the average total ChBF, ChBF(AV). Responses of ChBF to various physiological stimuli, su ch as increased blood O-2 and CO2 concentrations, rapid increases in i ntraocular pressure, and valsalva maneuvers, were documented. Results. Significant correlations were obtained between the ChBF(AV) values me asured with both flowmeters (P < 0.001) and between the ChBF(AV) value s measured in the right and left eye (P < 0.001). ChBF(P) represented less than 23% of ChBF(AV). ChBF(AV) was not significantly affected by 5 minutes of breathing 100% oxygen. Raising end-tidal COP in one subje ct from 37 to 59 mm Hg increased ChBF(AV) by approximately 40%. Acute elevation of the intraocular pressure by suction cup or finger pressur e on the globe reduced ChBF(AV) by as much as 90%. Valsalva maneuvers induced reproducible responses that were very different from those rec orded 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 measur ements of relative choroidal blood flow in the foveal region of the hu man fundus. Near-infrared laser diodes enable measurements through und ilated pupils. Examples of responses suggest new avenues in the invest igation by LDF of the effect of various physiological stimuli, pharmac ologic agents, and pathologic processes on the choroidal circulation i n man.