Effect of dark adaptation on retinal blood flow

Purpose: Laser Doppler measurements performed immediately after the transit ion from dark adpatation (DA) to light led to the hypothesis that retinal b lood flow, F-ret, is increased during DA, but the use of visible lasers had prevented measurements during DA. Our aim was to test this hypothesis by m easuring F-ret during and after DA. Material and methods: F-ret in retinal vessels at the optic disk surface wa s recorded quasi-continuously in one eye of 6 normal subjects (age 27 to 60 years) using a laser Doppler flowmeter in the near-infrared (810 nm). Meas urements were performed during light (baseline), various periods of DA and again during light. DA lasted between 2 and 32 min. Results: Average F-ret for the 6 subjects did not change significantly (-2. 7 +/- 8% sd, p > 0.05) during the various periods of DA, as determined from linear regressions of the flux versus time. Following the transition from DA to light, there was, in most cases, a rapid transient increase of the fl ux, which reached an average value of 37+/-10% above the pre-transition val ue and peaked at 30-60 sec after the transition. Conclusions: These results do not support the hypothesis that F-ret in norm al volunteers is increased during DA. Rather, they strongly suggest that th e transient increase in flux observed after DA is induced by the transition from dark to light (FNSRS #3200-043157 et CNR, It. #95.01715.CT04).