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Blind Patients: Retinal Implant for Recognizing Letters

Blind Patients: Retinal Implant for Recognizing Letters

photo: blind patient reading a word 

Researchers have shown that a light-sensitive chip, implanted beneath the retina, is able to restore meaningful images in blind patients, up to the point of recognizing letters and words.

The subretinal electronic implant is based on 1500 light-sensitive diodes, amplifiers and electrodes on a subretinal chip that transforms images into a grid of electrical impulses that are transmitted to the brain via retinal neurons.

Previously blind patients were able to recognize and localize sources of light or whitish objects. One of the patients was able to correctly identify unknown objects and to read the hands of a large clock. Furthermore, he was able to recognize individual letters, to form words out of these letters and to distinguish seven different shades of grey. However, in cases where the retina is scarred, insufficiently perfused or where the optic nerve is damaged, chip-mediated vision cannot be achieved.

The research aims at using a retinal implant to replace the lost function of degenerated rods and cones in the retina in patients blind from Retinitis pigmentosa, for example. Retinitis pigmentosa, a hereditary retinal degeneration, is one of the most frequent causes of blindness at a young age.

Fifteen years of research headed by Prof. Dr. Eberhart Zrenner at the Research Institute of Ophthalmology at the University of Tuebingen were necessary to find the materials that would at the same time be biocompatible while sufficiently protecting the sensitive electronic system. It was important to determine the minimum and maximum electrical current for stimulating the optic nerve via the retina and its remaining inner nerve cell network responsible for processing and transmitting visual information to the brain.

Ophthalmic surgeons had to develop a new surgical technique, enabling them to slide the chip beneath the retina while at the same time creating a connection via electric cable from inside the eye to a place behind the ear to power the chip and to provide external control and monitoring of the chip function.; Source: University Hospital Tübingen

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