The World of Biometrics - Retina Identification

Introduction

Retinal identification (RI) is an automatic method that provides true identification of the person by acquiring an internal body image, the retina/choroid of a willing person who must cooperate in a way that would be difficult to counterfeit.

Awareness of the uniqueness of the retinal vascular pattern dates back to 1935 when two ophthalmologists, Drs. Carleton Simon and Isodore Goldstein, while studying eye disease, made a startling discovery: every eye has its own totally unique pattern of blood vessels. They subsequently published a paper on the use of retinal photographs for identifying people based on blood vessel patterns

Later in the 1950's, their conclusions were supported by Dr. Paul Tower in the course of his study of identical twins He noted that, of any two persons, identical twins would be the most likely to have similar retinal vascular patterns. However, Tower's study showed that of all the factors compared between twins, retinal vascular patterns showed the least similarity.

The eye shares the same stable environment as the brain and among physical features unique to individuals, none is more stable than the retinal vascular pattern.
Because of its internal location, the retina/choroid is protected from variations caused by exposure to the external environment (as in the case of fingerprints, palmprints etc.).

A retinal scan machine from Optavue

Functions

The functions of a basic RI system are:
1. Enrollment - where a person's reference eye signature is built and a PIN number and text (such as the person's name) is associated with it.
2. Verification - a person previously enrolled claims an identity by entering a PIN number. The RI scans the ID subject’s eye and compares it with the reference eye signature associated with the entered PIN. If a match occurs, access is allowed.
3. Recognition - RI scans the ID subject’s eye and “looks-up” the correct, if any, reference eye signature. If a match occurs, access is allowed.

Eye Signature

The representation of retina is derived from a retina scan composed of an annular region of retina, scan circle . The spot size (width of annular band) and scan circle size are chosen to return sufficient light and contrast detail in the worst case (very small eye pupil) to support the performance specification of the RI.Two major representations for the RI eye signature have emerged. The original representation consisted of 40 bytes of contrast information encoded as real and imaginary coordinates in the frequency domain and was generated with the fast fourier transform. The second representation, while slightly larger at 48 bytes, leaves the contrast data in the time domain. The primary advantage of the time domain representation of the eye signature is computing efficiency resulting in lower computer cost and/or higher processing speed.Taking the ratio of the brightness at any point to the average regional brightness removes artifacts that are due to non-uniformity of the beam at the point where it enters the eye. This also normalizes the identifying signal for varying pupil sizes that greatly influence the total light returned to the detector.The fully processed digital eye signature can be described as a normalized contrast waveform of the entire scan circle. Average RMS contrast averages approximately 1.5 to 4% of the total light detected. The contrast maximum is the brightest reflection from the scan circle and the contrast minimum is the darkest reflection from the scan
circle. The waveform is normalized so that the maximum or the minimum is at the 4 bit limit (either +7 or –8, respectively) to fully utilize digital dynamic range.The simplest form of the RI reference eye signature is an array of 96 four-bit contrast numbers for each of 96 equally spaced scan circle positions for a timedomain pattern of 48 bytes per eye. An optional 49th byte carries the AC RMS value of the waveform to be used for equalizing the RMS values of the acquired and reference waveforms in the correlation (match) routine.

Technology

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 undetectable ray of low-energy infrared light into a person’s eye as they look through the scanner's eyepiece. This beam of light outlines a circular path on the retina. Because retinal blood vessels are more sensitive to light than the rest of the eye, the amount of reflection fluctuates. The results of the scan are converted to computer code and stored in a database.

Performance

Many tests of performance of the retina/choroid scanning technology described have taken place, some with databases of several hundred individual eyes. Sandia National Laboratory has tested the products of EyeDentify and reported no false accepts and a three-attempt false reject error rate of less than 1.0%

Pros and Cons

Advantages

* 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

Disadvantages
* 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 costs

Uses

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 applications. 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.