Retina and cornea scanners are real technologies, with retinal scanners specifically analyzing the unique pattern of blood vessels in the eye, similar to fingerprints. While there is some confusion about corneal scanners, they likely refer to iris scanners that assess the color patterns of the iris. Concerns were raised about the stability of blood vessel patterns over time, but it is believed that their relative positions remain consistent despite potential damage. Multi-point matching techniques, akin to those used in fingerprint recognition, may be employed to ensure accurate identification. For further information, resources like "How Stuff Works" can provide valuable insights into biometrics.