New Type of Retinal Prosthesis Could Better Restore Sight to Blind
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Using tiny solar-panel-like cells surgically placed underneath the retina, scientists at the Stanford University School of Medicine have devised a system that may someday restore sight to people who have lost vision because of certain types of degenerative eye diseases.
Data stream from a video camera is processed by a pocket PC, and the resulting images are displayed on a liquid crystal microdisplay (LCD), similar to video goggles. The LCD corresponding to approximately 30 degrees of visual field is illuminated with a pulsed (0.5 ms) near-infrared (~900 nm) light, projecting the images through the eye optics onto the retina. The IR image is then received by the photovoltaic pixels in a subretinally implanted chip. Each pixel converts the pulsed light into a proportional pulsed bi-phasic electric current that introduces visual information into diseased retinal tissue. Retinal chip is approximately 3 mm in diameter, corresponding to 10 degrees of visual field. The 30 degree visual field is accessible by eye scanning.
Credit: Stanford University School of Medicine
Optical approach to information delivery allows for simultaneous activation of thousands of pixels in the implant, and retains a natural link between the eye movements and the visual perception. Since each photovoltaic pixel operates independently, they do not need to be physically connected to each other. Thus, segments of the array may be separately placed into the subretinal space, greatly simplifying surgery.
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 microdisplay 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.