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Y. Okawa, T. Fujikado, T. Miyoshi, Y. Hirohara, T. Mihashi, Y. Tano; Evaluation of Suprachoroidal–Transretinal Stimulation (STS) by Optical Imaging . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4072.
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© ARVO (1962-2015); The Authors (2016-present)
Activated neural tissues can be visualized by optical imaging by measuring stimulus–evoked changes of light reflectance. Recently, this technique has been applied to retina to detect light–evoked retinal response (Tsunoda et al, IOVS, 2004). We developed a prototype optical–imaging fundus camera. We examine the change of light reflectance evoked by electrical stimulation using suprachoroidal–transretinal stimulation (STS), which has been employed for artificial retina (Kanda et al, IOVS, 2004).
Four eyes of four cats were studied under general anesthesia. A small retinal area was focally stimulated with electric currents between an active electrode placed on the fenestrated sclera and a reference electrode inserted into the vitreous cavity. Biphasic pulses were applied for 4 seconds with a frequency of 50Hz, duration 0.5msec, and current of 15 to 300µA. Fundus images in the near–infrared (800–880nm) were obtained in every 20msec for 26 seconds between 2 seconds before and 20 seconds after stimulation. To improve S/N ratio, 20 images of 20 consecutive experiments were averaged. Two–dimensional topography was constructed by subtracting images before stimulation from those after stimulation.
About 600msec after STS onset, a concentric low–reflectance area (LRA) was observed around the retinal locus that was pressed by the electrode from sclera side. The diameter of LRA increased concomitantly with the increase of current intensity (60–150µA). LRA was not detected with a current less than 60µA, and was saturated with a current above 150µA. The radius of LRA with 60µA stimulation was about 3 degrees in visual angle and was similar to that evaluated by electrophysiological method (Kanda et al, ARVO 2004).
Optical imaging in response to STS showed a localized LRA. The threshold current intensity and the retinal area activated by STS were similar to those evaluated by electrophysiological method. These data suggest that LRA reflects retinal neuronal activity by electrical stimulation. This is the first report of retinal optical imaging that detected change of light reflectance evoked by electric stimulation.
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