Flicker-evoked Changes in Human Optic Nerve Blood Flow: Relationship with Retinal Neural Activity

Purpose: Visual flicker induces a response in human optic nerve blood flow (F(onh)) and inner retinal activity, as assessed by laser Doppler flowmetry and electroretinogram (ERG), respectively. In this study the relationship was examined between the flicker-evoked changes in F(onh) (RF(onh)) and ERG when various parameters of the stimulus were varied.

Methods: In five normal observers (mean age, 41; range, 25-62 years) F(onh) and ERG were recorded simultaneously in response to pure red (R) or pure green (G) flicker, as well as heterochromatic R-G flicker (30 degrees field at the posterior pole). RF(onh) and the changes in the first (1F) and second (2F) harmonic amplitudes of the ERG were documented as a function of the frequency of pure luminance and equiluminant R-G flicker, the mean illuminance of 10-Hz luminance flicker, and the color ratio r = R/(R + G) of a 15-Hz heterochromatic R-G flicker.

Results: Frequency-dependent changes in RF(onh) were similar to those in both 1F and 2F amplitudes for equiluminant R-G flicker. RF(onh) and 2F amplitude increased and then saturated with increasing mean illuminance of luminance flicker. They both decreased similarly as the R-G flicker approached the r value corresponding to equiluminance. RF(onh) was positively correlated with both 1F and 2F amplitudes (r = 0.55 and 0.31, respectively, P < 0.05) when these quantities were recorded as a function of frequency of R-G equiluminant flicker. RF(onh) was positively correlated with 2F amplitudes when both quantities were recorded as a function of mean illuminance of luminance flicker and r of heterochromatic R-G flicker (r = 0.52 and 0.48, respectively, P < or = 0.01).

Conclusions: Under specific experimental conditions, changes in human RF(onh) are similar to and correlated with those of the flicker ERG 1F and 2F amplitudes. These findings support a relationship between vaso- and neural activity changes in the neural tissue of the human eye.