A retinal scan, commonly confused with the more appropriately named "iris scanner", is a biometric technique that uses the unique patterns on a person's retina to identify them. It is not to be confused with another ocular-based technology, iris recognition. The biometric use of this scan is used to examine the pattern of blood vessels at the back of the eye.
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 so complex that even identical twins do not share a similar pattern.
Although retinal patterns may be altered in cases of diabetes, glaucoma or retinal degenerative disorders, the retina typically remains unchanged from birth until death. Due to its unique and unchanging nature, the retina appears to be the most precise and reliable biometric. Advocates of retinal scanning have concluded that it is so accurate that its error rate is estimated to be only one in a million.
A biometric identifier known as a retinal scan is used to map the unique patterns of a person's retina. The blood vessels within the retina absorb light more readily than the surrounding tissue and are easily identified with appropriate lighting. 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 are more absorbent of this light than the rest of the eye, the amount of reflection varies during the scan. The pattern of variations is converted to computer code and stored in a database.
The idea for retinal identification was first conceived by Dr. Carleton Simon and Dr. Isadore Goldstein and was published in the New York State Journal of Medicine in 1935. The idea was a little before its time, but once technology caught up, the concept for a retinal scanning device emerged in 1975. In 1976, Robert "Buzz" Hill formed a corporation named EyeDentify, Inc., and made a full-time effort to research and develop such a device. In 1978, specific means for a retinal scanner was patented, followed by a commercial model in 1981.
In popular culture 
The relative obscurity and "high tech" nature of retinal scans means that they are a frequent device in fiction to suggest that an area has been particularly strongly secured against intrusion. Some notable examples include:
In the 1982 movie "Star Trek: The Wrath of Khan", Admiral Kirk gains access to top secret computer files by use of a retinal scan.
In the 1966 movie Batman, Batman describes to Robin how the tiny vessels in the retina are unique to the individual and utilizing the portable retina scan device in the Batmobile they could confirm the identity of the Penguin.
Characters in the 1996 film Mission: Impossible, the film Paycheck, the 1995 film GoldenEye, the 1996 film Barb Wire, the 1999 film Entrapment, and the 2002 film Minority Report utilize or try to deceive retinal scanners.
In the 'Splinter Cell' series, retinal scanners are used to identify agents within Third Echleon and guards within military/business complexes.
Retinal scanners are typically used for authentication and identification purposes. Retinal scanning has been utilized by several government agencies including the FBI, CIA, and NASA. However, in recent years, retinal scanning has become more commercially popular. Retinal scanning has been used in prisons, for ATM identity verification and the prevention of welfare fraud.Retinal scanning also has medical application. Communicable illnesses such as AIDS, syphilis, malaria, chicken pox and Lyme disease as well as hereditary diseases like leukemia, lymphoma, and sickle cell anemia impact the eyes. Pregnancy also affects the eyes. Likewise, indications of chronic health conditions such as congestive heart failure, atherosclerosis, and cholesterol issues first appear in the eyes.
Pros and cons 
- Low occurrence of false positives
- Extremely low (almost 0%) false negative rates
- Highly reliable because no two people have the same retinal pattern
- Speedy results: Identity of the subject is verified very quickly
- Measurement accuracy can be affected by a disease such as cataracts
- Measurement accuracy can also be affected by severe astigmatism
- Scanning procedure is perceived by some as invasive
- Not very user friendly
- Subject being scanned must be close to the camera optics
- High equipment cost
See also 
- Retina and Iris Scans. Encyclopedia of Espionage, Intelligence, and Security. Copyright © 2004 by The Gale Group, Inc.
- Retinography: How Retinal Scanning Works. Retrieved on 2007-04-02.
- “Eye Prints,” TIME Magazine, Dec. 16, 1935. Retrieved on 2008-04-10.
- Hill, Robert. “Retina Identification”. Msu.Edu. Retrieved on 2007-04-02
- "Why retina scanning works better for James Bond than it ever would for us".
- Iris/Retinal Identification. Wcu.Edu. Retrieved on 2007-04-02.
- Ostaff, Courtney. “Retinal Scans Do More Than Let You In The Door." Retrieved on 2007-04-02.
- Roberts, Chris. "Biometrics" Retrieved on 2009-06-11.