Concepts

The flicker test: neurovascular coupling

When retinal neurons work harder, nearby vessels widen to bring more blood: neurovascular coupling.[26] A flickering light drives the retina while a camera measures the diameter of a retinal artery or vein second by second.

The standard recording lasts 350 s: a 50 s baseline, then three cycles of 20 s flicker at 12.5 Hz and 80 s recovery.[27] Healthy vessels widen by a few percent during flicker and relax afterwards; in glaucoma the response is smaller[28] and slower.[29]

Vessel width, % change from baseline+0.1%
flicker onthreshold 2% (±0.5 borderline)-202460 s20 s40 s60 s80 s
━ measured by the tracker from the video┅ true width (known, because the video is synthetic)t = 0 s · 8× speed

Pick a vessel and run the test. A healthy vessel widens by a few percent while the light flickers.

Interactive Synthetic dataRun the test yourself: a simulated retinal vessel under 20 s of flickering light, measured frame by frame by GlaucomAI's vessel tracker. The video is synthetic, so its true width is known.
Standard recording, 350 s (12.5 Hz flicker, 25 video frames per second)
0 s50150250350 s
flicker onGlaucomAI threshold 2% (±0.5 borderline)-1012345020406080seconds from flicker onset (average of 3 cycles)% diameter changepreserved · max 4.2%impaired · max 1.2%
Synthetic dataSynthetic patients DEMO-02 and DEMO-01: responses measured by GlaucomAI's tracker from simulated video, averaged over the three cycles.
Key facts
  • In early glaucoma, flicker-induced widening of the retinal veins was significantly smaller than in healthy volunteers.[28]
  • Eyes with glaucoma or ocular hypertension showed smaller and delayed responses.[29]
  • GlaucomAI's tracker cancels eye movement by phase correlation[30] and measures the vessel's width at half depth on 40 profiles per frame.
In GlaucomAI

No public dataset has flicker recordings with glaucoma labels, so the tracker is validated on synthetic video with a known answer. The 2% (±0.5) threshold is a placeholder until real recordings exist.

References on this page

  1. 26.Riva CE, Logean E, Falsini B. Visually evoked hemodynamical response and assessment of neurovascular coupling in the optic nerve and retina. Prog Retin Eye Res. 2005;24(2):183–215. PubMed search ↗
  2. 27.Garhöfer G, Bek T, Boehm AG, et al. Use of the retinal vessel analyzer in ocular blood flow research. Acta Ophthalmol. 2010;88(7):717–722. DOI ↗
  3. 28.Garhöfer G, Zawinka C, Resch H, Huemer KH, Schmetterer L, Dorner GT. Response of retinal vessel diameters to flicker stimulation in patients with early open angle glaucoma. J Glaucoma. 2004;13(4):340–344. PubMed ↗
  4. 29.Gugleta K, Kochkorov A, Waldmann N, et al. Dynamics of retinal vessel response to flicker light in glaucoma patients and ocular hypertensives. Graefes Arch Clin Exp Ophthalmol. 2012;250(4):589–594. DOI ↗
  5. 30.Kuglin CD, Hines DC. The phase correlation image alignment method. Proc IEEE Int Conf on Cybernetics and Society. 1975:163–165. Google Scholar ↗
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