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I.M. Lanzl, W. Vilser, K.E. Kotliar; Retinal Vessel Reactions to Modulations of Chromatic Luminance Flicker Parameters . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3915.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Exposing the healthy human retina to flickering light causes retinal arterial dilation and subsequent reactive vessel constriction. We examined the vessel response to two different mixed luminance–chromatic flicker stimuli at different flicker frequencies. Methods: In 10 young, healthy volunteers the Retinal Vessel Analyzer was applied to assess retinal arterial diameters. Baseline measurement was performed for one minute. A flicker light consisting of red (600 – 720 nm) – green (530 – 570 nm) or blue (430 – 520 nm) – green (530 – 570 nm) with a flicker frequency of 2, 6, 12, 16 or 20 Hz was applied for 30 sec. All experiments were repeated 3 times. 12 Hz stimulation was repeated after 1 week with the same volunteers. Results: With both tested chromatic flickering lights a prompt vessel dilation of retinal arteries in comparison to baseline could be determined in all volunteers (p<0.001). On average with red–green flicker this amounted to 1.2% ± 0.6% after 2 Hz stimulation; to 2.5% ± 1.0% at 6 Hz; to 3.5% ± 1.4% at 12 Hz; to 3.6% ± 1.3% at 16 Hz and to 3.9% ± 1.5% at 20 Hz. With blue–green flicker we found a dilation of 3.6% ± 1.3% after 2 Hz stimulation, of 3.5% ± 1.4% at 6 Hz; of 3.4% ± 1.1% at 12 Hz; of 2.3% ± 1.4% at 16 Hz and of 2.0% ± 1.5% at 20 Hz. After flicker stimulation a reactive arterial constriction occurs. The maximal constriction increases with increasing frequency of the stimulus in both tested types of flicker. The repeat experiment using 30 sec stimulation after one week showed no statistical difference to the first series (p>0.2). Conclusions: We consider the observed effects to be a manifestation of neuro–vascular coupling and consequently autoregulation of retinal vessels. Red–green flicker demonstrated an increase in dilation magnitude with increased stimulus frequency from 2 Hz to 20 Hz. In contrast blue–green flicker stimulation showed a decrease in maximal dilation amplitude with frequency increase. We consider a flicker stimulus of 30 sec duration to constitute an appropriate stimulus for further investigation of retinal vessel regulation in physiological and in pathological situations. It remains to be determined in future studies, whether any of the two different color mixed luminance flicker stimuli is more adequate to identify vascular changes in different diseases.
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