Abstract
Abstract: :
Purpose: To establish the time course, magnitude and reproducibility of optic nerve blood velocity (Vel), volume (Vol) and flow (F) in response to luminance flicker in normal subjects. Methods: In 15 subjects (28-63 years), Vel, Vol and F (LDF parameters) were continuously recorded by near-infrared laser Doppler flowmetry from temporal sites of the optic disk. Stimuli consisted of 15-Hz green diffuse flicker (field of 30°, 13 lux, duration 50s). Magnitude (M) of the responses were expressed as the % change between the mean of the values during the last 20 s of flicker and the mean of those during the last 20 s of baseline. Time constant (τ) of the group average increases in the LDF parameters in response to flicker were determined. Intra-subject coefficients of variation (CV) were obtained for 6 successive F-responses (RF) (1 subject) and multiple RFs recorded over a 3 months period (2 subjects). Fatigue effects of the flicker-induced LDF parameter responses were assessed based on 8-11 min stimulation. Results: Group average (± 95% CL) of all LDF parameters increased during flicker (p<0.00002, Table). Intra-subject CV for 6 recordings was 26% for RF and CVs for 2 subjects (3 months) were 25 and 50%. We found no dependence of RF on the pre-stimulus F and no fatigue effect on RF. Conclusions: RF is predominately determined by changes in blood volume, suggesting that the increase in flow is mainly due to a local vasodilatation or capillary recruitment during flicker. The time courses of the flow parameters are similar to those found in the human cortex in response to visual stimulation.
Keywords: blood supply • optic disc • retina