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Optic nerve and choroidal blood flow in humans by laser Doppler flowmetry

Laser Doppler flowmetry (LDF) was applied to measure blood flow in discrete regions of the optic nerve head (ONHBF) and in the foveal region of the choroid (ChBF) in humans. LDF is based on the Doppler effect. For its ocular application, a diode laser beam (wavelength equals 810 nm, 60 mW at the cornea) was delivered to the eye through a fundus camera. For ONHBF the beam was directed at regions of the optic disk with no apparent individual vessels. For ChBF in the foveal region subjects were asked to look directly at the beam. Light scattered by red blood cells in the tissue volume illuminated by the incident laser beam was detected at the fundus image plane of the camera by an optical fiber. Two analysis schemes of the Doppler signal were developed: one uses commercial skin blood flowmeters, the other a NeXT station (Motorola 68040 based) computer system. Responses of ONHBF and ChBF to various physiological and pharmacological stimuli were obtained and shown to be in agreement with previously published findings. LDF is a valid technique for obtaining non- invasive, continuous and sensitive recordings of ONHBF and foveal ChBF, the latter without the need to dilate the pupil.