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M.D. Abramoff, Y.H. Kwon, D. Ts'o, P. Soliz, S. Berriga, R. Kardon; Imaging of Retinal Function in Awake Humans: Timecourse of the Functional Signal in Response to Focal Visual Stimulation . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5697.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the timecourse of the functional imaging signal derived from changes in infrared reflected light from the retina elicited by visual stimulation.
5 normal subjects were studied. Changes in retinal reflectance of light (wavelength 780nm) were measured using an optical imaging device, consisting of a modified fundus camera with a cooled CCD camera and a head restraint device. Visual stimuli, either a bright stationary vertical bar or a blank stimulus, were projected centrally onto the retina from an LCD screen through the camera optics. Reflectance images were collected every 333ms for 60 seconds in 10 cycles, each consisting of 3 seconds of either a vertical bar or a blank stimulus and 3 seconds of no stimulus for recovery. Stimuli were given in a random block fashion; each run contained 5 vertical bar and 5 blank cycles. The images in each run were registered to the first image. A ratio r, the average pixel intensity i in a rectangular region of interest (ROI) where the vertical bar had been projected, divided by i in a perpendicular ROI where no stimulus had been projected, was computed for each image. The timecourse of r was plotted for each cycle and analyzed with a mixed model of repeat measurements.
48 runs were obtained. In all subjects, in cycles with a vertical bar, r was found to exhibit a significant gradual decrease, but not in cycles with a blank. The decrease in r typically reached its maximum of 0.3% at approximately 2 seconds after stimulus onset.
There is a consistent, small decrease in infrared fundus reflectance in regions of retina exposed to a vertical bar stimulus in all subjects tested. The timecourse and polarity of the signal make it unlikely that it is a consequence of bleaching. The signal is presumed to represent a manifestation of the functional activity of the retina in response to a visual stimulus. Imaging of retinal function may help in understanding the spatial and temporal characteristics of retinal activation by visual stimulation in humans.
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