Biometric Eye Scans

The identification of a victim or suspect of a crime can result from comparison of information collected during a forensic examination with information residing in various data bases. One example includes fingerprints. The Integrated Automated Fingerprint Identification System that is maintained by the Federal Bureau of Investigation is a repository for millions of fingerprint patterns and other information. Another example is the pattern obtained from a scan of the retina and iris, both parts of the eye.

The retina is the neural part of the eye responsible for vision. The pattern of blood vessels serving the retina is unique to an individual, and is as unique as fingerprints. The chance that two people will have the same iris pattern is estimated to be one in 10⁷⁸.

The technology that scans the retina is known as retinal scanning. The true target for the scan is the capillary pattern in the retina. The process relies on generating images of the retina using a low intensity light source. In 1930s retinal capillary patterns were suggested to be unique, but the technology to use this information was developed much later. Although military and high-security use of photographic retinal scans began decades earlier, by 1985, retinal scan technology became available for computerized biometric identification and commercial security use.

Retinal scans are just one of the biometric methods using the eye for personal identification. Two years after the first retinal scanner was developed, in 1987, Leonard Flom and Aram Safir patented the use of iris patterns as a personal identifier. However, it was not until 1994 when John Daugman developed the technology for iris scanning. Since then iris scanning technology began to challenge the retinal scans. Currently a number of companies claiming that they perform retinal scanning, in reality are performing iris scans.

Retinal scans are based on the presence of the fine network of capillaries supplying retina with oxygen and nutrients. These vessels absorb light and can be easily visualized with proper illumination. Retinal scans require close contact of user and scanner, a perfect alignment of the eye with a scanner, and no movement of the eye. The examiner is required keep the subject's eye within half an inch (1cm) of the instrument. The subject must focus on a little green light (to properly align the eye) and avoid blinking. A low intensity coherent light is then transmitted through the eye and the reflected image of the retinal capillary pattern is recorded by the computer.

Although retinal patterns are generally thought to be constant during a person's life, they can change in case of diabetes, glaucoma, retinal degenerative disorders or cataracts. Therefore, although retinal scans are nearly 100% accurate, they cannot be used as a universal security measure without making allowances for normal age-related physiological changes.

An initial scan (enrollment) takes a minimum of five scans and lasts approximately 45 seconds; subsequent authentication scans are faster and take only 10–15 seconds. An acquired image containing 320–400 reference points is converted to a map of the retina and used to identify a match from the templates encoded in the scanner's software. Retinal images captured are extremely small, only 35 bytes in size.

The technology for retinal scans has changed in recent years. The initial large devices are being followed now by smaller and more accurate instruments. The first commercial retinal scanner was developed in 1984. One of the most recent developments in the area is a small mobile and easy to use retinal scanner. Although it was initially developed for diagnostic purposes, it will be available as a security tool as well.

Fooling the retinal scanner is very difficult, as it requires intact retina to complete a scan. Following death, the retina degrades very quickly and thus cannot be used in most cases for accurate post-mortem identification. Although often a popular movie special effect, using a retina detached from a cadaver would fail with modern scanning equipment. Likewise, surgical alteration of the retinal pattern would be not only a dangerous and extremely expensive process, but futile, as the changes introduced would be readily detected by modern scanning equipment.

Iris scans use characteristics more similar to fingerprints than to retinal vein pattern. The colored part of the eye appears to be as unique as fingerprints and retinas. Scanning technology takes advantage of crypts, furrows, ridges, striations, ligaments, and collarette. While 240 points are recorded, the image size is 512 bytes, over ten times larger than a retinal scan. The main advantage of the iris scans is the ability to perform them from a distance of up to three feet and short time of scan of only 20 seconds initially, with subsequent identification requiring only two seconds. Glasses and contact lenses do not interfere with the scanning process and identification.

In contrast to the retinal scanners, iris scanners are of two main types: active and passive. The active system works from 3–14 inches (7.5–35 cm) and also requires the user to move forward and backward so the camera is adjusted properly. In contrast the passive system can work over longer distance from one to three feet (0.3–1 m).

Biometric techniques are used in identification and authentication. The features used for the two processes can overlap, or can be different. Authentication requires high accuracy to ensure restricted access. Retinal and iris scans offer high accuracy, and the primary users of retinal scans are military and government facilities, such as CIA, FBI , and NASA. Scans are used to control access to high security areas.

An acceptance is growing for the iris recognition systems and they are now used by government agencies, commercial companies, and also in the public sector. Among the government users are the U.S. Congress, and Departments of Defense, State, and Treasury. Some of the commercial companies that protect themselves by using iris recognition are Bank United, GTE, Hewlett Packard, Lockheed Martin, and British Telecom.

Scanning is also being implemented at airports as an added security feature. For example, as of 2005, eight of the largest Canadian airports (Toronto, Vancouver, Ottawa, Montreal, Halifax, Winnipeg, Calgary, and Edmonton) have, or are planning to install, systems that will be part of the U.S. Customs inspection process.

see also Fingerprint; Identification.