A retinal scan is a biometric technique that uses the unique patterns on a person's retina blood vessels. It is not to be confused with another ocular-based technology, iris recognition, commonly called an "iris scanner."
The human retina is a thin tissue composed of neural cells that is located in the posterior portion of the eye. Because of the complex structure of the capillaries that supply the retina with blood, each person's retina is unique. The network of blood vessels in the retina is not entirely genetically determined and thus even identical twins do not share a similar pattern.
A retinal scan is performed by casting an unperceived beam of low-energy infrared light into a person’s eye as they look through the scanner's eyepiece. This beam of light traces a standardized path on the retina. Because retinal blood vessels absorb light more readily than the surrounding tissue, the amount of reflection varies during the scan. The pattern of variations is digitized and stored in a database.