The human retina is a thin tissue made up 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 not entirely genetically determined and thus 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, aside from DNA .The National Center for State Courts estimate that retinal scanning has an error rate of one in ten million
A retinal scan is performed by casting an unp erceived 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 absorb light more readily than the surrounding tissue, the amount of reflection varies during the scan. The pattern of variations is digitized and stored in a database
The Process of Retinal Recognition:
Unlike the other Biometric modalities, Retinal Recognition requires a great amount of cooperation from the end user to collect high quality, raw images. This requires that the end user must be in very close proximity to the Retinal scanning device. This is in sharp contrast to Iris Recognition, where images can be collected from a very far distance.
The process can be broken down as follows:
1.Image/Signal Acquisition and Processing:
In this first phase, the individual must place their eye into a tiny receptacle. From here, an infrared light beam light is then “shot” into the eye, in order to fully illuminate the Retina. To get the best quality, raw images of the Retina, this light is shone into the eye in a 360-degree manner. This process can take as long as a few minutes. In order to make sure that resilient images are captured, the individual must remain perfectly still while the infrared light completes its rotation. Any eyeglasses must be removed, in order to avoid any signal interference (in other words, this would cause the infrared light beam to reflect back into the scanning device without having captured any actual images). At this stage, up to five raw images can be collected and analyzed, in order to create the composite image from which the unique features will be extracted.
2.Enrollment and Verification Template Creation:
In this second phase, the unique features are then extracted. Genetic factors actually do not dictate the composition of the blood vessel pattern which make up the Retina. In other words, this is not written into the DNA structure of the individual and is not handed down to the offspring. Because of this, up to 400 unique data points can be captured from the Retina, unlike the fingerprint, where only 30-40 unique data points can be captured. After this has been done, the Enrollment Template is then created. The size of the Retinal Enrollment Template is only at 96 bytes. Thus, it is also deemed to be the smallest Biometric Template of all. This is, of course, has numerous advantages to it. First, there is much lower processing overhead required when examining the statistical closeness between the Verification and Enrollment Templates. Second, this small size means that a greater number of templates can be stored in a single database, and optimizing it will be much more efficient when compared to a database of Facial Recognition Templates, where the sizes are much larger. This same process is also used to create the Verification Template.
Because Retinal Recognition requires such a close proximity to the end user, there are a number of variables or factors which can greatly influence the quality of the raw images which are collected. This, in turn, can also have a huge impact on the quality of the Enrollment and Verification Templates as well.
These factors are as follows:
- Lack of cooperation on part of the individual:
As it has been described, the individual must remain perfectly still throughout the above-described process, especially when the raw images are being captured. Any sudden or unintentional movement can negatively affect the lens alignment of the aperture which is used to transmit the infrared light beam into the Retina.
- The distance between the individual’s eye and the lens is too far:
For a high-quality scan to take place, there must be a distance of not greater than 3 inches between the receptacle and the Retina. If the distance is greater than this, then the scanning process must be repeated over again until it is correct. In this regard, when compared to the other Biometric modalities, precision is of utmost importance in Retinal Recognition.
- The size of the individual’s pupil:
A smaller than average size pupil can greatly reduce the amount of external light which is transmitted to the Retina. This problem can become further exacerbated if the pupil constricts even further because of inconsistent lighting conditions.
- The Retina is deemed to be very stable, and hardly ever changes over the lifetime an individual. Thus, in this regard, it is considered to be the most reliable Biometric Technology which is available in the marketplace today.
- Given the small file size of the Retinal Recognition Templates, the time it takes for the system to confirm the identity of an individual is very quick; it can take place in just less than two seconds.
- Because of the high number of unique data points the Retina possesses, there is almost no error that when an identity of an individual is confirmed, it is truly that person. In other words, the statistical probability of an impostor being falsely accepted by a Retinal Recognition System is almost nonexistent.
- Since the Retina is located from within the structure of the eye itself, it is not prone to the harshness of the external environment like Hand Geometry Recognition and Fingerprint Recognition.
- Overall, there is a very negative attitude about using Retinal Recognition amongst the public, at least here in the United States. For example, because of the sheer intrusiveness which is involved with it, many people perceive that it poses a serious health risk to the eye. There have been no documented cases in this regard.
- There is a very strong unease about having to place the eye into a receptacle and having an infrared light beam being shone directly onto it.
- When compared to all of the other Biometric modalities, Retinal Recognition demands the highest levels of cooperation and motivation from the end user to capture high quality, raw images. As a result, the Ability to Verify metric can be as low as 85% (other modalities are as high as 99% or even 100%),
- Because of the attention that is required by the end user, it can take numerous attempts and a long time to get the results which are required. Thus, as a result, if the process is not done correctly, it can lead to a very large False Rejection Rate (this occurs when a legitimate individual is improperly denied access to either physical or logical based resources by the Retinal Recognition System).