The fundus was examined under green light.
At the start of the study the ophthalmological baseline status was determined and mydriasis was induced with tropicamide. One eye of five healthy volunteers (mean age 33.8 (SD 1.6) years, refractive error <1 dioptre) was examined.
LIGHT RESPONSE STUDY IN QUANTUMWISE OFFLINE
The changes are quantifiable by an online automated technique based on the RVA, 19– 21 as well as by offline analysis of digital images. Periodic changes of the observation light simulate luminance flicker to induce diameter changes in retinal arterioles The present study tested the following hypotheses: A flicker characterised by a stronger contrast can induce possibly a greater change in the calibre of retinal vessels and could be a preferred method for investigating vessel reactivity. 18 With its constant, relatively bright observation light and a superimposed flicker light, the technique used in the latter study does not produce an optimal luminance flicker. 17 Investigations with the RVA under green light with additional blue flicker light showed a change in the arterial vessel diameter of up to +4.2%. 16 Analysis of retinal vessel diameters in fundus photographs demonstrated vessel dilation immediately after flicker provocation. 12, 13 A number of studies have improved our understanding of the ocular neurovascular coupling of flicker induced blood flow changes in the optic papilla by LDV 11, 13– 15 and have established correlations with functional parameters such as electroretinography. 11 Animal experiments have shown an increase in laser Doppler blood flow in the optic nerve head in response to flicker light. The term denotes illumination alternating in brightness (luminance flicker) or colour (equiluminant chromatic flicker) at a frequency of approximately 1–50 Hz. 10 An artificial form of light exposure is flicker light. 9 Orienting studies on the diameter of major retinal vessels using the retinal vessel analyser (RVA) have also shown blood flow to increase with brightness. 1– 6 Clinical investigations have demonstrated increased blood flow rates of the light adapted eye compared to darkness in the optic nerve and choroid by laser Doppler velocimetry (LDV) 7, 8 and in the ophthalmic artery and central retinal artery by the duplex method.
Modern imaging techniques have shown that enhanced neuronal activity leads to increased blood flow in corresponding areas of the brain. The authors believe that the method is suitable for the quantitative investigation of retinal vasosclerosis, especially in association with arteriosclerotic and hypertensive systemic disease. In the RVA measurements a minimum of −4.6% (1.9%) (p = 0.01) was measured 22 (4.7) seconds after the end of flicker exposure.Ĭonclusion: Flicker evoked response for retinal arterioles was found both by RVA and by analysis of flash images. In both techniques the vascular diameter overshot the baseline approximately 10 seconds. The maximum induced dilation reached at the end of the flicker period was +7.4% (SD 2.4%) in the RVA measurements and +3.5% (0.8%) in the photographs (p = 0.01).
Results: An arterial diameter response to flicker light was found both by RVA and by analysis of flash images (p<0.001). The arterial diameter response to flicker light (12.5 Hz, 530–600 nm, duration 20 seconds) was automatically and continuously measured online three times by retinal vessel analyser (RVA) and once offline from flash images using the VesselMap program. Methods: One randomised eye of five healthy subjects (mean age 33.8 (SD 1.6) years) was examined. Aim: To investigate diameter changes in retinal arterioles in response to flicker variations of the examination light.
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