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J.V. Lovasik, H. Kergoat, M. Parent; Effect of Flicker on the Micropulses Atop Real–Time Measurements of Retinal Vessels in Humans . Invest. Ophthalmol. Vis. Sci. 2006;47(13):496.
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The Imedos Retinal Vessel Analyser (RVA) is a system for in vivo measurements of retinal vessel diameter in real–time. An improved resolution in the RVA has allowed detection of minute sinusoidal–like pulses on arteries and veins. The etiology and physiological role of these newly reported micropulses (MP) remain unknown. We examined the interaction between MP amplitude and light–induced changes in the cross–sectional diameter of the vessels.
20 healthy adults (Avg. Age: 23.1 ± 1.9 years) volunteered for this study. The responses to flicker at 12.5Hz presented for 20s and 60s were recorded continuously throughout 3 separate trials for each subject. The vessels analyzed were about 1disc diameter from the optic nerve head in the superior–temporal retina.
The group–averaged vasodilation elicited by the 20s and 60s flicker times was between 3.5% and 6.5%. While the amplitude of MPs was reduced by flicker, it increased progressively over time during the flicker interval in both arteries and veins; subsequently the MP amplitude decreased progressively when flicker was stopped (p< 0.04). The maximal MP amplitude for the 60s flicker time exceeded that for 20s by 12 to 19%.
Flicker induced vasodilation likely reflected the need for increased retinal perfusion subsequent to a light–induced increase in neural retinal activity. Because the MP frequency correlated with the cardiac pulse, and arteries and veins had the same pulse frequency, we concluded that the vessel pulse was of cardiac origin. The progressive increase of MP amplitude during flicker was attributed to viscoelastic properties of the vessels and changes in vessel blood volume. Non–invasive quantification of vessel pulses may provide useful clinical indices of cardiovascular function.
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