Optical imaging to evaluate retinal activation by electrical currents using suprachoroidal-transretinal stimulation.

PURPOSE To determine whether reflectance changes of the retina after electrical suprachoroidal-transretinal stimulation (STS) can be detected with a newly developed optical imaging fundus camera. METHODS Ten eyes of 10 cats were studied. A small retinal area was focally stimulated with electric currents passing between an active electrode placed in the fenestrated sclera and a reference electrode in the vitreous. Biphasic pulses were applied for 4 seconds with a current up to 500 muA. Images of the fundus illuminated with near-infrared (800-880 nm) light were obtained every 20 msec for 26 seconds between 2 seconds before and 20 seconds after the STS. Twenty images of 20 consecutive experiments were averaged. A two-dimensional map of the reflectance changes was constructed by subtracting the images before the stimulation from those after the stimulation. STS-evoked potentials (EPs) were recorded from the optic chiasma. RESULTS Approximately 0.5 second after the onset of STS, reflectance changes were observed around the retinal locus, where the stimulating electrodes were positioned. The intensity of the reflectance changes was correlated with the intensity of the stimulus current. The area of the reflectance change increased as the current intensity increased and was correlated with the amplitude of the EPs (R(2) = 0.82). CONCLUSIONS Reflectance changes after STS were localized to the area around the electrode. The strong correlation between the area of the reflectance changes and the amplitude of the EPs suggested that the reflectance changes reflected the activity of retinal neurons elicited by electrical stimulation.