Retinal Prostheses

Excerpt

Retina prostheses try to reactivate the residual circuitry in a blind patient’s retina to produce a synthetic form of usable vision. Using an array of stimulus electrodes or light-sensitive proteins, the neurons in the degenerate retinal network are activated to elicit a series of light percepts termed “phosphenes”. If the patient’s phosphenes act as independent spatial percepts in their visual field, a crude type of form vision may be achieved. This form vision could improve a visually impaired patient’s ability to orient to landmarks in foreign visual environments, avoid obstacles, and improve social interactions. While most retinal prostheses in the current clinical trials rely on stimulation by electrical pulses from electrode arrays to locally excite the patient’s retinal neurons, several research groups are also trying more biologically compatible stimulation methods termed “optogenetics” which deploy viruses to transduce light-activated stimulator protein genes into select groups of retinal neurons which when expressed modulate their neural activity. Each technology presents different challenges and benefits for biological integration into the blind patient’s degenerate retina. Coupling and replacing the lost retinal neurons in the central fovea remains a challenge for both electronic and optogenetic combination therapies. There are many common issues involved in the real-world assessment of patient visual benefit from these novel medical technologies. Given the heterogeneity of RP as a disease, the availability of multiple therapies may be useful for patients, each offering different advantages for their type of retinal degeneration and its degree of progression.