APR 22, 2011
The authors conducted this laboratory study to assess which retinal cells are principally activated by transcorneal electrical stimulation (TES), which has the potential to evaluate residual retinal function in patients with advanced retinitis pigmentosa. They used optical functional imaging to compare retinal reflectance changes (RCs) elicited by TES to those elicited by electrical stimulation of the optic chiasma in cats. The results indicate that TES principally activates retinal ganglion cells (RGCs), with a change in blood flow initiated afterward. These findings suggest that TES could be used to ascertain whether residual RGCs are functional and provide information about whether a patient is a suitable candidate for a retinal prosthesis.
The authors compared RCs elicited by TES at 20 Hz for 5 ms to those elicited by electrical stimulation (ES) at 100 Hz for 50 μs of the optic chiasma in two eyes of two cats under general anesthesia. Near-infrared fundus images were observed with a modified fundus camera for 26 seconds, beginning 2 seconds before and ending 20 seconds after the 4-second long electrical stimulation. RCs were observed at the optic disc, retinal arteries and retinal veins. The authors also determined the effect of an intravitreal injection of tetrodotoxin on the RCs elicited by electrical stimulation.
They found that the two-dimensional maps of the RCs elicited by both TES and optic chiasma stimulation were similar. The latency of the RCs ranged from 2.0 to 4.0 seconds, with the peak occurring 6 to 9 seconds after the onset of electrical stimulation. The intensity of the RCs was correlated with the amplitude of electrically evoked potentials elicited by TES stimulation. The RCs disappeared after tetrodotoxin injection in both the TES and optic chiasma stimulation.