How many types of non-optical aids for visually challenged persons are used?

Non-optical aids include visual aids, tactual aids (using the sense of touch), auditory aids (using the sense of hearing) and electronic aids. With the help of visual aids, required size of words, suitable intensity of light and material at proper distances can be provided. Tactual aids including Braille writer, slate and stylus help the visually challenged persons in taking notes, reading and writing and in learning mathematics. Auditory aids include cassette, tape recorders, talking books and other such programs. Electronic aids such as talking calculators are also available for performing many computations. Closed circuit television, also an electronic aid, enlarges printed material with suitable contrast and illumination. Nowadays, use of audio CDs and voice boxes with the computers are also very helpful for listening and writing the desired text.