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G. Hanazono, K. Tsunoda, K. Inomata, Y. Kazato, M. Tanifuji; Flash-Evoked Light Reflectance Changes of the Optic Disk Reflect the Neural Activity of the Inner Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):528.
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Optical imaging technique with intrinsic signals can non-invasively map the neural activity of the retina by measuring flash-evoked reflectance changes of infrared light (Tsunoda, et al., IOVS, 2004, vol. 45, no. 10, pp 3820-6). The light reflectance changes can also be observed at the optic disk (Crittin,et al., Neurosci Lett. 2004;360:141-4.), however, the source of the signal has not been fully understood. In order to clarify the origin of the signal at the optic disk, we have investigated 1) time courses of the flash-evoked light reflectance changes at different wavelengths of the observation light , and 2) flash-evoked blood flow changes, at the optic disk.
The ocular fundus of a Rhesus monkey was monitored under anesthesia to measure the intrinsic signals evoked by a white diffuse flash stimulus. We have measured 1) the intrinsic signal of the optic disk under the observation light with different wavelengths (840nm, 630nm and 570nm),and 2) the flash-evoked blood flow changes of the optic disk by laser doppler flowmetry (Periflux PF5000, Perimed. Sweden), by inserting the laser probe (1.0 mm in diameter) to the vitreous cavity through pars plana.
The normalized timecourses of the optic disk were identical at three different wavelengths of the observation light. The blood flow increased following a flash stimulus (1.0-2.0%) and the time courses were almost the same as that of the intrinsic signals.
The flash-evoked reflectance changes of infrared light at the optic disk are not related to the changes in the oxygenation level of hemoglobin, and mainly reflect the blood flow (or volume) increase evoked by the flash. This system may have a potential as a diagnostic tool for evaluating the inner retinal function objectively.
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