The Distribution of Retinal Responsiveness Evoked by Trans-Scleral Electrical Stimulation Observed by Intrinsic Signal Imaging in Macaque Monkey

Abstract

Purpose:: Recently, the electrical stimulation of retina has been clinically applied both for the treatment of optic nerve diseases, such as ischemic optic neuropathy (Fujikado, et al., JJO, 2006), and for the elucidation of disease processes (Geckler, et al., IOVS, 2006). Phosphene sensation can be perceived in the visual field by the electrical stimulation of retina, however, it is very difficult to quantitatively describe its strength and spatial extension over the visual field. In order to evaluate how the current affects the retinal responsiveness spatially, we have measured the spatial distribution of electrically evoked retinal responsiveness by the intrinsic signal imaging technique, which can map the stimulus-evoked retinal responsiveness by a CCD camera (Tsunoda, et al., IOVS, 2004).

Methods:: A DTL electrode was set in the lower fornix and the reference electrode was placed in a wrist of anesthetized rhesus monkey. Biphasic pulse electricity was given through the sclera in various conditions (light- or dark-adapted condition, current: 0 - 1000 µA, frequency: 10 - 100 Hz, stimulus duration: 0.5 - 7.0 sec). The intrinsic signals (light reflectance changes in the posterior retina following electrical stimulation) were measured with infrared observation light.

Results:: The intrinsic signals were observed in the posterior retina and the optic disk with the current at ~ 50 µA. The signal intensities increased significantly with higher current. The signal was homogeneously distributed over the whole posterior retina, including the fovea. The thresholds and amplitudes were almost equal in dark- and light-adapted conditions. The signal amplitude at the optic disk was the maximum with the current at 20 Hz.

Conclusions:: The spatial distribution of electrically evoked responsiveness could be quantitatively evaluated by the intrinsic signal imaging technique. We think that this imaging method is useful for investigating the basic properties of electrically evoked responses in retina.

Keywords: imaging/image analysis: non-clinical • retina: proximal (bipolar, amacrine, and ganglion cells)