Evaluation of Phosphene Evoked by Transcorneal Electrical Stimulation Using Indirect Pupillary Reflex

Abstract

Abstract: : Purpose: The success of the visual recovery by artificial retina (AR) or stem cell transplantation (ST) in eyes suffering from retinal degeneration depends upon the preserved activity of inner retinal cells. In eyes with extensive loss of photoreceptors, we cannot evaluate their preserved retinal activity (PRA) with the conventional light evoked potential. Electrical evoked response (EER), an objective measure of phosphene, is recorded by transcorneal electrical stimulation (TES) and is originated by the activation of inner retinal layers (Miyake, 1980). To prevent the potential side effect of the repetitive electrical stimulation, we investigated the possibility to evaluate the phosphene quantitatively by a single stimulation using indirect pupillary reflex. Methods: We examined the phosphene evoked by TES on three healthy volunteers. To evaluate the phosphene quantitatively, we measured the pupillary reflex of the fellow eye using video-pupillography. We used contact lens electrode (Burian-Allen type) for stimulating the eye. Biphasic rectangular pulse was applied to the electrode via an isolator. The relationship between the pupillary response and the current intensity was investigated. The pupillary response was evaluated with contraction rate (CR) that was calculated as the change of pupil diameter divided by the original pupil diameter. Results: All subjects perceived phosphene at the center of visual field with a current intensity of 100±20 µA. The CR increased linearly with the current intensity from 3% at 100µA to 6.5% at 200µA. Conclusions: Indirect pupillary reflex was recorded by TES with low stimulus intensity and was linearly increased with the increase of stimulus intensity. This method may be useful to evaluate the residual retinal function in eyes with photoreceptor damage.

Keywords: degenerations/dystrophies • electrophysiology: clinical • pupillary reflex