By Helen Albert, Senior medwireNews Reporter
An implanted retinal prosthesis, consisting of an array of electrodes linked up to a video camera and wearable computer, allows blind patients to successfully "read" two-to-four letter braille words.
"In this clinical test with a single blind patient, we bypassed the camera that is the usual input for the implant and directly stimulated the retina," explained lead researcher Thomas Lauritzen (Second Sight Medical Products, Sylmar, California, USA) in a press statement.
"Instead of feeling the braille on the tips of his fingers, the patient could see the patterns we projected and then read individual letters in less than a second with up to 89% accuracy," he added.
The prosthesis, known as the Argus II (Second Sight Medical Products, Sylmar, California, USA), works by translating a signal from a small camera mounted on a pair of glasses and translating the information into electrical stimulation on the electrodes implanted in the patient's retina (10x6 array).
It has recently been approved for use in Europe and has been implanted in over 50 patients to date. It is currently in clinical trials in the USA. The 60 electrode Argus II prosthesis is an update on the original Argus I prosthesis, first implanted in 2002, which had 16 electrodes.
For this study, published in to Frontiers in Neuroprosthetics, Lauritzen and team tested the accuracy of the Argus II for reading braille words in a single male volunteer with the implant by bypassing the camera and stimulating the electrodes directly.
As braille letters are formed using a 3x2 array of six dots, six electrodes out of the 60 in the Argus II implant were selected for stimulation. The participant was tested on his recognition of single letters and of two-to-four letter words spelled out letter by letter in braille.
Overall, he correctly identified 89% of the single letters, and 80%, 60%, and 70% of two-, three-, and four-letter words, respectively.
"There was no input except the electrode stimulation and the patient recognized the braille letters easily. This proves that the patient has good spatial resolution because he could easily distinguish between signals on different, individual electrodes," said Lauritzen.
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