Abstract
Purpose:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
Keywords: 550 imaging/image analysis: clinical •
688 retina •
499 diabetic retinopathy