In the United States more than a million people are legally blind. The
development of an effective visual prosthetic device is therefore of major
importance. Attempts to come up with visual prostheses has a long history.
There have been numerous approaches with varied underlying philosophies.
Non-invasive approaches have had considerable success. Some of these provide
the visual information normally used by sighted individuals through other
modalities. An example of this approach is Brill where the printed text
is converted into somatosensory signals.