Retinography

Retinography is a sophisticated means for identifying people by the pattern of blood vessels on the retina (the innermost coat of the back part of the eye). It requires the use of a special scanner about the size of a shoe-box that can map the unique pattern of blood vessels on the retina. The pattern is so complex that even identical twins do not have the same blood vessel configuration. Those who favor its use claim retinography has an error rate of only one in a million.

There are currently a number of biometric devices in use, machines that can identify people by their physical characteristics. Some examples include fingerprint scanners and devices that can recognize a particular voice, hand, or signature. The retinal scanner is another addition to the identification tool kit.

How Retinal Scanning Works

A retinal scanner uses infrared light for mapping. As a person looks into the eyepiece, an invisible beam of low-energy infrared light traces a circular path on the retina at the back of the eye. The blood-filled capillaries absorb more of the infrared light than the surrounding tissue. Because of this, there is a variation in the intensity of the reflection. The scanner measures this reflection at 320 points along the beam path. It then assigns an intensity grade between zero and 4,095. The resulting numbers are compressed into an 80-byte computer code. This code can then be compared with patterns that have already been entered into the computer's data base.

Applications

Retina scans are already in use in the Pentagon and government and corporate organizations where people need to be identified before they can enter an area. New concerns about security from terrorism and bank and credit card fraud have caused many organizations to think seriously of using retina scans or other biometric means to identify people at airports and ATM machines.

Some states require that truck and bus drivers be mapped by retinography. This information is used by state agencies to prevent bad drivers from holding licenses in several states to hide their driving records. A proposed—and more controversial—use of retina scans is to develop a worker registry, where everyone is scanned to make sure that they are legal citizens of the United States, and thus eligible for employment. Critics of this proposal are concerned about possible invasions of privacy and violations of other personal rights.

Advantages and Disadvantages

Retinal scanners have several advantages over fingerprinting and voice recognition systems. They do not require as much computer memory as a fingerprint scan, and they are not subject to contamination from dirt or finger misplacement. Unlike voice recognition systems, retinal scanner are not distracted by background noise or changes in voice caused by illness.

The main disadvantage of the retinal scanner is that the person has to focus on the scanner from about three inches away. This restriction makes the device difficult for ATM use because a person using a cash machine rarely focuses on one area very long and is never close enough. A new device called an iris scanner may prove more useful for these casual transactions, since the scanning camera can be farther away and only has to scan the pattern of the iris (colored portion) of the eye, a procedure which does not require focusing on the camera.