[Effect of chromatic flicker on circulation of the optic nerve].
OBJECTIVE
To determine the response of human optic nerve head (ONH) blood flow (delta F) to heterochromatic equiluminant flicker modulation (eql-fl) and compare it to the response induced by pure luminance flicker (l-fl).


METHODS
In 5 normal volunteers the ONH blood flow was measured by conventional laser Doppler flowmetry. Stimuli were generated by green and red light emitting diodes and delivered to the eye through a fundus camera illumination optic. Both green and red illuminances were square wave modulated in counter phase at different frequencies between 2 and 40 Hz. delta F was defined as the ratio between the ONH blood flow after 1 min stimulation and a baseline blood flow measured prior to the stimulation.


RESULTS
In response to a 2 Hz eql-fl, ONH blood flow increases by 36% in average. delta F versus flicker frequency displayed the characteristics of a low-pass function with a cutoff frequency of 10 Hz for an eql-fl and a band-pass function with broad maximum around 10 Hz for the I-fl.


CONCLUSIONS
delta F in human ONH can be evoked by heterochromatic equiluminant flicker modulation. The blood flow frequency response to eql-fl and I-fl are similar to the neural activity dominated by the Parvo- and Magno-cellular activity, respectively. These findings offer a new approach to study the neurovascular coupling at the ONH in both physiological and diseased conditions involving predominantly or selectively the Magno- and Parvo-pathways.
Logean
E
E
Institut de Recherche en Ophtalmologie (IRO), Grand-Champsec 64, CP 4168, CH-1950 Sion 4, Suisse.
Falsini
B
B
Riva
C E
CE
D000328:Adult; D003118:Color Perception / Q000502:physiology*; D005260:Female; D005425:Flicker Fusion / Q000502:physiology*; D006801:Humans; D017078:Laser-Doppler Flowmetry; D008297:Male; D008875:Middle Aged; D009900:Optic Nerve / Q000098:blood supply*; D010775:Photic Stimulation; D012039:Regional Blood Flow / Q000502:physiology