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Jonathan Noonan, Ryan Man, Thanh Nguyen, Jie Jin Wang, Ecosse Lamoureux; Retinal Arteriolar Dilation to Flicker Light is Reduced with Repeated Stimulation. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5830.
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© ARVO (1962-2015); The Authors (2016-present)
Flicker light-induced retinal vasodilation, a marker of dynamic retinal function that is impaired in patients with diabetes or diabetic retinopathy, is reproducible when repeated at one hour but the effect of short-term repeated stimulation is unknown. We investigated the impact of restimulation after five and thirty minutes on the reproducibility of retinal arteriolar and venular dilations.
The flicker light response was measured in non-smokers without any chronic medical conditions using the Dynamic Vessel Analyzer (DVA, IMEDOS, Germany). A temporal arteriole and venule segment was selected while the fundus was examined under red-free light. Baseline diameters were recorded for 50 seconds, followed by 20 seconds of flickering light and an 80 second recovery period. The 100-second flicker cycle was repeated twice per test. The flicker light response test was repeated after 5 and 30 minutes rest. Maximum vessel dilation was calculated as the average maximum percentage increase in vessel diameter during flicker stimulation compared to that before stimulation. Within-subject differences were assessed using repeated measure analysis of variance.
19 participants were recruited (74% female; mean ± SD age 33 ± 5.9 years). Mean ± SD maximum arteriole dilations during stimulation were at baseline: 3.27 ± 2.10%; after five minutes: 2.68 ± 1.89%; and after a further thirty minutes: 3.28 ± 2.09%. Maximum arteriolar dilation was significantly reduced when repeated after five minutes (p = 0.048) but not after thirty minutes (p = 0.958) compared to the baseline test. Corresponding mean ± SD maximum venule dilations were 4.56 ± 1.48%, 4.16 ± 1.61% and 4.61 ± 1.66%, respectively, without statistically significant differences (p > 0.05 for all). Arteriole and venule diameters before flicker stimulation were not significantly different between baseline and repeated tests.
Repeated flicker light stimulation within five minutes, but not thirty minutes, appears to reduce retinal arteriolar vasodilations in healthy humans. This temporal effect, probably due to a bleaching of photoreceptors or exhaustion of dilatory molecules, suggests that sufficient recovery time is needed to ensure reliable measurements in repeated measure designs.
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