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(Investigative Ophthalmology and Visual Science. 2006;47:715-721.)
© 2006 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.05-0008
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Visual Stimulus–Induced Changes in Human Near-Infrared Fundus Reflectance

Michael D. Abràmoff,1,2 Young H. Kwon,1 Dan Ts’o,3 Peter Soliz,4 Bridget Zimmerman,5 Joel Pokorny,6 and Randy Kardon1,2

1From the Department of Ophthalmology and Visual Sciences, University of Iowa Hospitals and Clinics, Iowa City, Iowa; the 2Department of Veterans Affairs, Iowa City VA Medical Center, Iowa City, Iowa; the 3Department of Neurosurgery, SUNY Health Sciences Center, Syracuse, New York; 4Visionquest Biomedical Inc., Albuquerque, New Mexico; the 5Department of Biostatistics, College of Public Health, University of Iowa, Iowa City, Iowa; and the 6Department of Ophthalmology and Visual Science, University of Chicago, Chicago, Illinois.

PURPOSE. Imaging studies from anesthetized feline, primate, and human retinas have revealed near-infrared fundus reflectance changes induced by visible light stimulation. In the present study, the spatial and temporal properties of similar changes were characterized in normal, awake humans.

METHODS. Five normal human subjects were studied. A modified fundus camera was used to image changes in retinal reflectance of 780-nm near-infrared light imaged onto a 12-bit charge-coupled device (CCD) camera in response to a green (540 nm) visual stimulus. During 60 seconds of recording (frame rate, 3 Hz) 10 cycles were recorded, during each of which 3 seconds of blank and then 3 seconds of either vertical bar or blank stimulus was projected. The change in the average near-infrared reflectance of the stimulated retinal region relative to an equal-sized nonstimulated region (r is the ratio of reflectance between the two retinal areas) was analyzed with a mixed model for repeated measures.

RESULTS. The mixed model showed a significant average decrease in r of 0.14% (95% CI, –0.25 to –0.03) over all subjects induced by bar stimulus cycles, with a gradual return to baseline after stimulus offset, compared with only a 0.04% (95% CI, –0.11–+0.20) decrease in r induced by blank, nonstimulated cycles. The mixed model for individuals showed a decreasing linear trend in r over time during bar stimulation, but no decrease for blank cycles in three of five subjects.

CONCLUSIONS. There was a localized decrease in reflectance in response to 780-nm near-infrared light in the retinal region exposed to a visual stimulus, which was significant in three of five subjects. It is presumed that the reflectance change represents the functional activity of the retina in response to a visual stimulus.




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