Retinal Prosthesis Could Better Restore Sight

Photo: Eye

Retina is a light-sensitive tissue
lining the inner surface of the
eye; ©
Paul Heubeck

This device — a new type of retinal prosthesis — involves a specially designed pair of goggles, which are equipped with a miniature camera and a pocket PC that is designed to process the visual data stream. The resulting images would be displayed on a liquid crystal micro display embedded in the goggles, similar to what's used in video goggles for gaming. Unlike the regular video goggles, though, the images would be beamed from the LCD using laser pulses of near-infrared light to a photovoltaic silicon chip — one-third as thin as a strand of hair — implanted beneath the retina.

Electric currents from the photodiodes on the chip would then trigger signals in the retina, which then flow to the brain, enabling a patient to regain vision.

A study discusses how scientists tested the photovoltaic stimulation using the prosthetic device's diode arrays in rat retinas in vitro and how they elicited electric responses, which are widely accepted indicators of visual activity, from retinal cells. The scientists are now testing the system in live rats, taking both physiological and behavioural measurements, and are hoping to find a sponsor to support tests in humans.

"It works like the solar panels on your roof, converting light into electric current," said Doctor Daniel Palanker. "But instead of the current flowing to your refrigerator, it flows into your retina."
There are several other retinal prostheses being developed, and at least two of them are in clinical trials. A device made by a Los Angeles-based company was approved in April for use in Europe, and another prosthesis-maker announced earlier this month results from its clinical testing in Europe.

Unlike these other devices — which require coils, cables or antennas inside the eye to deliver power and information to the retinal implant — the Stanford device uses near-infrared light to transmit images, thereby avoiding any need for wires and cables, and making the device thin and easily implantable.

"The current implants are very bulky, and the surgery to place the intraocular wiring for receiving, processing and power is difficult," Palanker said. The device developed by his team, he noted, has virtually all of the hardware incorporated externally into the goggles. "The surgeon needs only to create a small pocket beneath the retina and then slip the photovoltaic cells inside it." What is more, one can tile these photovoltaic cells in larger numbers inside the eye to provide a wider field of view than the other systems can offer, he added.; Source: Stanford University School of Medicine