Ocular electrical stimulation: Therapeutic application and active retinal implants for hereditary retinal degenerations

Abstract

Electrical stimulation has a long history in ophthalmology. Subthreshold electrical stimulation can have beneficial therapeutic effects on hereditary degenerative retinal diseases. Suprathreshold stimulation is able to elicit visual perceptions and, if multielectrode fields are arranged as an array, usable pictures can be perceived by blind patients. This is a review article on the current situation and studies on therapeutic transcorneal electrical stimulation. Moreover, the challenges, surgical concepts and visual results of active retinal implants are discussed. This article gives an overview on transcorneal electrical stimulation and active retinal implants based on published results, with special emphasis on the clinical application. The results of initial controlled studies on therapeutic transcorneal electrical stimulation in hereditary retinal diseases were very promising. The largest controlled study so far in patients with retinitis pigmentosa (RP) has yielded many positive trends and some significant improvements in electrophysiological data. Currently, two retinal implants have regulatory approval, the Argus II retinal prosthesis system® (SecondSight®) and the Alpha-IMS© (Retina Implant AG). Both systems can be used to improve visual perception and under test conditions can achieve visual acuities of 0.02 and 0.04, respectively. In-depth analyses and follow-up studies in larger patient groups are currently planned to definitively clarify the potential of therapeutic transcorneal electrical stimulation in RP patients. The challenges of currently available active retinal implants are the technical biostability and the limited spatial resolution.