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K. Tsunoda, G. Hanazono, M. Tanifuji; Sources of Retinal Intrinsic Signals Measured by in vivo Optical Imaging From Macaque Ocular Fundus . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3939.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Optical imaging with intrinsic signals is a reliable technique to map the functional organization of neural tissues by measuring stimulus–evoked light reflectance changes. Recently, this technique has visualized stimulus–induced response topography of cone and rod photoreceptors in Macaque retina (Tsunoda, et al., IOVS, 2004, vol. 45, no. 10, ‘Mapping Cone– and Rod–Induced Retinal Responsiveness in Macaque Retina by Optical Imaging.’). The source of intrinsic signals in retina, however, has not been fully understood because the light reflectance change under a certain wavelength of light depends on several independent mechanisms, which are difficult to be separately measured. In order to clarify the origin of the retinal signal, we have investigated the timecourses of the light reflectance changes from discrete regions in the ocular fundus at different wavelengths of the observation light. Methods: The ocular fundus of a Rhesus monkey, under anesthesia, was monitored via a modified fundus camera equipped with a CCD camera. The intrinsic signals evoked by white diffuse flash stimuli were calculated as a ratio of the averaged images obtained after stimulus to those obtained before the stimulus onset. Results: Under infrared observation light (850nm), the light reflectance from the fovea and peri–macular region rapidly decreased and reached its peak within 100 ms. On the other hand, the light reflectance from the optic disc gradually decreased and reached its peak 2.0 to 3.0 s following stimulus onset. Under visible observation light (650nm), the light reflectance from the fovea increased and that from the peri–macular region decreased following stimulus onset. Conclusions: The fast darkening at the foveal center, which is composed of cones and free of capillaries, indicates that tissue light scattering is the major source of intrinsic signals in retina under infrared observation light. The slow darkening at the optic disc, which is composed of axons, glial cells and vessels, indicates that the stimulus–induced blood flow change can be detected as the reflectance change from the optic disc. The recording under visible observation light detects the light reflectance changes following the bleaching of photopigments.
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