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Charles E. Riva, Benedetto Falsini, Eric Logean; Flicker-Evoked Responses of Human Optic Nerve Head Blood Flow: Luminance versus Chromatic Modulation. Invest. Ophthalmol. Vis. Sci. 2001;42(3):756-762.
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purpose. To determine the response of human optic nerve head blood flow
(RFonh) to heterochromatic equiluminant flicker
modulation and compare it to the response induced by pure luminance
methods. In five normal volunteers, Fonh measured at the
neuroretinal rim was monitored continuously by laser Doppler flowmetry.
Stimuli were generated by green and red light emitting diodes and
delivered to the fundus in Maxwellian view (field of 25o).
Both green (G) and red (R)
illuminances were square-wave modulated, 180o out of phase,
with a maximum value of 10.4 for G and 2.64 lux for R. Flicker frequency was varied from 2 Hz to 40 Hz. RFonh was defined as the change in
Fonh during stimulation relative to the prestimulus
results. Defining the color ratio r as R/(R + G), the RFonh, measured for a 15-Hz flicker, was largest
at pure luminance (r = 0 and 1), declined at mixed
luminance and chromatic modulations, and reached a secondary maximum at r = 0.45, the value of psychophysical
equiluminance. RFonh versus flicker frequency
displayed the characteristics of a low-pass function for the
equiluminance flicker stimulus and of a band-pass function, with a
maximum at intermediate frequencies, for the luminance flicker
conclusions. RFonh in humans can be evoked by heterochromatic
flicker, modulated either in luminance or chromatic equiluminant
conditions. RFonh may be specific for luminance
and chromatic modulations, similar to neural responses dominated by the
magno- and parvocellular activity, respectively. These findings offer a
new approach to study the neurovascular coupling at the optic nerve
head in both physiological and diseased conditions involving
predominantly or selectively the magno- and parvocellular
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