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J. V. Lovasik, H. Kergoat, R. Parmar, M. Parent; Aging Eyes May Require Greater Blood Flow to Sustain Normal Vision. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5011.
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Abnormal ocular blood flow (OBF) seems to be involved in sight threatening diseases like glaucoma. Studies using Laser Doppler flowmetry have reported that blood flow in the optic nerve head (ONH) in response to flicker is greater in normal eyes than in eyes with ocular hypertension or primary open angle glaucoma. In this study we used digital imaging to measure changes in ONH luminance associated with flicker. Our objective was to determine whether changes in the ONH luminance are valid indices of blood flow.
A Retinal Vessel Analyzer (Imedos) normally used to measure dynamic changes in vessel diameter in response to flicker was modified to also record relative luminance values for selected circular areas on the ONH in 97 healthy adult volunteers, 20 to 80 years of age. Eye tracking capability allowed the luminance of a specific area on the ONH to be followed at 30 frames per second before, during, and after three consecutive 60sec flicker (12.5Hz) and three 60sec recovery intervals. The video camera recording the ONH was shielded electronically from the green flicker used to increase retinal activity. Flicker related changes in the ONH luminance were expressed as percent change from the steady-state record immediately prior to the flicker. The relationship between flicker-induced luminance change and subject age was modeled by linear regression (p<0.05).
Pre-Flicker recordings of ONH luminance revealed small spontaneous oscillations whose frequency matched the subject's heart rate. Each flicker period caused a biphasic reduction in the ONH luminance that reached a maximum within ~30 seconds. When flicker stopped, the luminance of the ONH increased monotonically to regain baseline within 20 seconds. The same response pattern was seen for the second and third flicker period. The maximum reduction in ONH luminance was calculated for each subject and it was seen to increase with age (p= 0.0401).
The systematic reduction in ONH luminance during flicker likely reflects changes in ONH perfusion (decreased luminance equals increased perfusion). The progressively larger changes in ONH luminance with age may indicate that aging eyes require greater perfusion to sustain normal vision. If so, this would place the aging eye at greater risk for ischemic neuropathy.
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