History
In 1935 an article appeared in the New York State Journal of Medicine suggesting that the pattern of blood vessels on the retina could be used to identify an individual. Since then, there has been extensive research dealing with the patterns and the uniqueness of the human eye, particularly the iris and retina. In 1987, Drs. Leonard Flom and Aram Safir were awarded the patent for researching and documenting the potential of using the iris as a unique identifier. However, the man generally credited with the responsibility for the development of the actual iris scanning technology is Dr. John Daugman, who developed the mathematical formulas used to measure the varying characteristics of one's iris at Cambridge University of England in 1994. 

How Iris/Retinal Scanning Works
Though iris and retinal scans both deal with the human eye, the processes in which they are done are extremely different. The iris (the colored portion of the eye) consists of over 400 distinguishing characteristics that can be quantified and used to identify an individual. However, only about 260 of those are captured in a "live" iris identification process by using such characteristics as contraction furrows, striations, filaments, crypts (darkened areas on the iris) and freckles (just to name a few). In identifying one's iris, there are two types of methods that are used by iris identification systems that are defined as passive and active. The active iris system method requires that a user be anywhere from six to 14 inches away from the camera. It also requires the user to move back and forth so that the camera can adjust and focus in on the user's iris. The passive system differs in that it allows the user to be anywhere from one to there feet away from the incorporated series of cameras that locate and focus in on the iris. There are four simple steps that follow:

1. A person stands in from of the iris identification system, between one and three feet away, while a wide-angle camera calculates the position of they eye. 
2. A second camera zooms in on the eye and takes a black and white image. 
3. Once the iris is in focus, it overlays a circular grid on the image of the iris and identifies the light and dark areas, like and "eyeprint". 
4. The captured image, or "eyeprint" is checked against a previously stored reference template in the database. 

Retinal Scan technology maps the capillary pattern of the retina, a thin nerve on the back of the eye. The subject is required to keep his or her head and eye motionless within a half-inch of the device, focusing on a small rotation point of green light, because it takes a minimum of five scans to enroll (which takes about 45 seconds). Infrared light is used because blood vessels on the retina absorb the light faster than the surrounding eye tissue. A video camera captures the retinal pattern and translates it into data that is 35 bytes in size. 

Where Iris/Retinal Scanning Is Being Used
Though iris/retinal scanning was used only for restricting access to highly sensitive government and military sites in the past, current movements are spreading across the US. One project that uses iris scan is that of Bank United, which has placed iris recognition devices in ATMs with in Kroger supermarkets in Texas and also a project demonstrated at Charlotte/Douglas International Airport in North Carolina. The Equine Research Institute in Utsunomiya, Japan, is using iris identification to identify racehorses. Retinal scanning devices have been placed in high security access control areas like the CIA, FBI and NASA. Some other more recent places where retinal scanning is being used are the Cook County Prison in Illinois and defense contractor, General Dynamics. 

Efficiency
The iris can have more than 250 distinct features, compared with 40 or 50 points of comparison in fingerprints, so iris scanning is an order of magnitude more accurate than fingerprints or even DNA analysis. One reason iris scanning is so efficient is that no two irises are alike, not even identical twins. According to mathematical code, the probability that two alike irises are one in ten to the 78th power (the population of the earth is approximately ten to the tenth power). Also, up to 100,000 records a second can be scanned using a standard personal computer; therefore the mismatch rate is less that one in 100,000. Iris scanning offers greater accuracy than finger scanning, voice or facial recognition, and hand geometry or keystroke analysis. In addition, it is safer and less invasive than retinal scanning. However, contact lens wearers or people with optical diseases like glaucoma may not easily pass an eyeball scan.

Though retinal scanning has several disadvantages like disease susceptibility, user unfriendly, and not enough funding, it continues to be one of the best biometric performers. Retinal scanning has a nearly zero percent false accept rate, small data template, and quick identify confirmations.