These devices are fitted in patients who have lost their vision through diseases such as retinitis pigmentosa that destroy the light-detecting cells in the eye but leave the vision-processing neurons intact. A chip is implanted in brain from which wires run to the retina. Also, there is a dial behind the ear that can be used to adjust brightness. Power to the device is provided via a battery kept in the pocket.
|Image Source: kurzweilai.net|
Earlier, Clinical Trials were run on Argus II, another visual prosthesis. The Argus II was approved by the US Food and Drug Administration (FDA) only a few weeks back. This device has been adapted to let blind people read Braille by sight rather than touch. However, the Argus II works very differently, it converts video from a camera on a pair of glasses into electronic signals “displayed” on a grid of 60 electrodes implanted over a person’s retina.
On the other hand, the Alpha IMS detects light entering the eye instead of using an external camera, which means that a patient can look around by moving their eyes rather than always having to move their head. A grid of 1500 electrodes are implanted underneath. It also makes use of the natural processing power of the neurons in the middle layer of the retina that process motion and contrast.