Retina scanning is a
biometric identification process that uses the unique pattern of
blood vessels on the retina in the back of the
eyeball to determine
identity.
In practice, the user puts their eye against a viewer, usually fitted with some kind of brace (usually a bow-shaped forehead pad) to reduce random motion in the head. (The eye must be held close to the reader because it has to look through the narrow opening of the iris, which significantly reduces the angle of view.) The image is then captured by a computer, which locates the spot where the blood vessels enter the eye (for a reference point), then matches the pattern of the vessels to the one in its memory.