*3.5.1. Sensing optical system*

vessel patterns show the least resemblance to all the other patterns examined. At that time,

With the concept of a simple fully automated device capable of retrieving a snapshot of the retina and verifying the identity of the user, *Robert Hill*, who established *EyeDentify* in 1975, devoted almost all of his time and effort to the development. However, functional devices did

Several other companies attempted to use the available fundus cameras and modify them to retrieve the image of the retina for identification purposes. However, these fundus cameras had several significant disadvantages, such as the relatively complicated alignment of the optical axis, visible light spectra, making the identification quite uncomfortable for the users,

Further experiments led to the use of infrared (IR) illumination, as these beams are almost transparent to the choroid that reflects this radiation to create an image of eye blood vessels. IR illumination is invisible to humans, so there is also no reduction in the pupil diameter

The first working prototype of the device was built in 1981. The device with an eye-optic camera used to illuminate the IR radiation was connected to an ordinary personal computer for image capture analysis. After extensive tests, a simple correlation comparison algorithm was

After another 4 years of hard work, EyeDentify Inc. launched the *EyeDentificationSystem 7.5*, where verification is performed based on the retina image and the PIN entered by the user

The device performed a circular snapshot of the retina. The image consisted of 256 twelve-bit logarithmic samples reduced to a reference record of 40 bytes for each eye. Contrast information is stored in the time domain. In addition, 32 bytes were added per each eye in the time

identification of the vessel's retina was a timeless thought.

and last but not least, the cost of these cameras were very high.

not appear on the market for several years.

**Figure 16.** Eye affected by toxoplasmosis.

22 Machine Learning and Biometrics

when the eye is irradiated.

chosen as the most appropriate.

with the data stored in the database.

domain to accelerate recognition.

Now, we introduce sensing devices that are used to capture images of the front or the back of the eye. The main ophthalmoscopic examination methods of the anterior and posterior parts of the eye include direct and indirect ophthalmoscopy as well as the most widely used examination, a *slit lamp* (see **Figure 17** on the left), which makes it possible to examine the anterior segment of the eye using the so-called *biomicroscopy*. *Fundus camera*, sometimes referred to as a *retinal camera*, is a special device for displaying the posterior segment of the optic nerve eye, the yellow spots, and the peripheral part of the retina (see **Figure 17** on the right). It works on the principle of indirect ophthalmoscopy where a source of primary white light is built inside the instrument. The light can be modified by different types of filters, and the optical system is focused on the patient's eye, where it reflects from the retina and points back to the fundus camera lens. There are mydriatic and non-mydriatic types that differ in whether or not the patient's eye must be taken into

**Figure 17.** (left) Slit lamp example [21] and (right) example of a non-mydriatic fundus camera [22].

mydriasis. The purpose of mydriasis is to extend the human eye's pupil so that the "inlet opening" is larger allowing one to be able to read a larger part of the retina. Certainly, non-mydriatic fundus cameras are preferred because the patient can immediately leave after the examination and can drive a motor vehicle, which is not possible in the case of mydriasis. However, in some patients, mydriasis is necessary. The price of these medical devices is in the order of tens of thousands of Euros, which is determined only by medical specialized workplaces.

The mechanical construction of the optical device is a rather complex matter. It is clear that the scanning device operates on the principle of medical eye-optic devices. These so-called retinoscopes, or fundus cameras, are relatively complicated devices, and the price for them is high as well.

The principle is still the same as for a retinoscope, where a beam of light is focused on the retina, and the CCD camera scans the reflected light. The beam of light from the retinoscope is adjusted so that the eye lens focuses on the surface of the retina. This reflects a portion of the transmitted light beam back to the ophthalmic lens that then readjusts it, the beam leaving the eye at the same angle below which the eye enters (return reflection). In this way, an image of the surface of the eye can be obtained at about 10° around the visual axis, as shown in **Figure 18**. The device performed a circular snapshot of the retina, mainly due to the reflection of light from the cornea, which would be unusable during raster scanning.

To ensure that the area is focused on the retina and that the eye of the user is in the axis of the scanning beam, the fixation point/target must be approximately in that same position throughout the scanning period. This can be a range of optical networks with focal distances of −7, −3, 0, and +3 diopters. It is expected that most users will be able to focus regardless of their optical defects. When the eye focuses on a target, the device automatically aligns itself to the axis by centering the rotating disc to the eye background. If a user aligns two or more optical patterns behind each other, the IR beam is centered on his or her pupil and the infor-

Recognition of Eye Characteristics

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Whenever a user looks into the camera's optical system, their head may be rotated slightly different from the original scanned position. The rotary algorithm (phase corrector) can rotate the data by several degrees. This process takes place several times until the best match is

• Using sampling, the eye reference is converted into a field with the same number of ele-

The comparator quality is given by the correlation value where the time shift is zero. It is in the range of +1 (absolute match) to −1 (absolute mismatch). Experience has shown that a score

The retinal representation is derived from a frame composed of annular regions (Eye-DentificationSystem 7.5 operates on a circular scanning principle). The size of the scanned area is selected for the worst possible scanning conditions (very small pupil) but is also

mation can be read.

reached, that is, the highest correlation.

of around 0.7 can be considered a match.

*3.5.3. Representation*

Comparison of the obtained samples is ensured in several steps:

**Figure 19.** The first version of EyeDentificationSystem 7.5 optical system.

ments as the field obtained, which ensures alignment (sample overlay).

• The field is correlated using a Fourier transform equivalent time domain.

• Both fields are normalized so that RMS is equal to 1, normalizing the intensity.

*3.5.2. Comparison*

The first products from EyeDentify used a relatively complicated optical system with rotating mirrors to cover the area of the retina—this system is described in U.S. Pat. No. 4,620,318 [23]. To align the scan axis and the visual axis, the so-called UV-IR cut filters (*Hot Mirrors*—reflects infrared light and passes through the visible light) are used in the design. A schematic drawing of the patent is shown in **Figure 19**. The distance between the eye and the lens was about 2–3 cm from the camera. The alignment system on the optical axis of the instrument is an important issue, and it is described in more detail in U.S. Pat. No. 4,923,297 [24].

Newer optical systems from EyeDentify are much easier and have the benefits of fixing optical axes with less user effort than the previous systems. The key part is a rotating scanning disc that carries multifocal Fresnel lenses. This construction is described in U.S. Pat. No. 5,532,771 [25].

**Figure 18.** Functional principle for obtaining a retinal image of the eye background.

**Figure 19.** The first version of EyeDentificationSystem 7.5 optical system.

To ensure that the area is focused on the retina and that the eye of the user is in the axis of the scanning beam, the fixation point/target must be approximately in that same position throughout the scanning period. This can be a range of optical networks with focal distances of −7, −3, 0, and +3 diopters. It is expected that most users will be able to focus regardless of their optical defects. When the eye focuses on a target, the device automatically aligns itself to the axis by centering the rotating disc to the eye background. If a user aligns two or more optical patterns behind each other, the IR beam is centered on his or her pupil and the information can be read.

#### *3.5.2. Comparison*

Whenever a user looks into the camera's optical system, their head may be rotated slightly different from the original scanned position. The rotary algorithm (phase corrector) can rotate the data by several degrees. This process takes place several times until the best match is reached, that is, the highest correlation.

Comparison of the obtained samples is ensured in several steps:


The comparator quality is given by the correlation value where the time shift is zero. It is in the range of +1 (absolute match) to −1 (absolute mismatch). Experience has shown that a score of around 0.7 can be considered a match.

#### *3.5.3. Representation*

**Figure 18.** Functional principle for obtaining a retinal image of the eye background.

mydriasis. The purpose of mydriasis is to extend the human eye's pupil so that the "inlet opening" is larger allowing one to be able to read a larger part of the retina. Certainly, non-mydriatic fundus cameras are preferred because the patient can immediately leave after the examination and can drive a motor vehicle, which is not possible in the case of mydriasis. However, in some patients, mydriasis is necessary. The price of these medical devices is in the order of tens of thou-

The mechanical construction of the optical device is a rather complex matter. It is clear that the scanning device operates on the principle of medical eye-optic devices. These so-called retinoscopes, or fundus cameras, are relatively complicated devices, and the price for them is

The principle is still the same as for a retinoscope, where a beam of light is focused on the retina, and the CCD camera scans the reflected light. The beam of light from the retinoscope is adjusted so that the eye lens focuses on the surface of the retina. This reflects a portion of the transmitted light beam back to the ophthalmic lens that then readjusts it, the beam leaving the eye at the same angle below which the eye enters (return reflection). In this way, an image of the surface of the eye can be obtained at about 10° around the visual axis, as shown in **Figure 18**. The device performed a circular snapshot of the retina, mainly due to the reflection of light

The first products from EyeDentify used a relatively complicated optical system with rotating mirrors to cover the area of the retina—this system is described in U.S. Pat. No. 4,620,318 [23]. To align the scan axis and the visual axis, the so-called UV-IR cut filters (*Hot Mirrors*—reflects infrared light and passes through the visible light) are used in the design. A schematic drawing of the patent is shown in **Figure 19**. The distance between the eye and the lens was about 2–3 cm from the camera. The alignment system on the optical axis of the instrument is an

Newer optical systems from EyeDentify are much easier and have the benefits of fixing optical axes with less user effort than the previous systems. The key part is a rotating scanning disc that carries multifocal Fresnel lenses. This construction is described in U.S. Pat. No. 5,532,771 [25].

important issue, and it is described in more detail in U.S. Pat. No. 4,923,297 [24].

sands of Euros, which is determined only by medical specialized workplaces.

from the cornea, which would be unusable during raster scanning.

high as well.

24 Machine Learning and Biometrics

The retinal representation is derived from a frame composed of annular regions (Eye-DentificationSystem 7.5 operates on a circular scanning principle). The size of the scanned area is selected for the worst possible scanning conditions (very small pupil) but is also sufficient for biometric identification. For these purposes, it is not necessary to obtain an image with too much area and resolution.

and extraction of bifurcations and crossings. For biometric systems, it should be noted that their use also includes the disclosure of information about their own health status since, as mentioned earlier, a relatively large amount of information on human health can be read from the image of an iris, and that is especially so from a retina as well. It is therefore up to each of us on how much we will protect this private information and whether or not we will use the systems. However, if the manufacturer guarantees that the health information does not get stored, and only the unique features are stored (not the image), then we all may be more than happy to use the system.

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Of popular biometrics, retinal recognition may be the most restrictive. They are not definite, but there is currently no system that can remove these shortcomings to a greater extent [20]:

• *Fear of eye damage*: the low level of IR illumination used in this type of device is completely harmless to the eye, but there is a myth among the lay public that these devices can damage

• *Outdoor and indoor use*: small pupils can increase the false reject rate. Since the light has to pass through the pupil twice (once in the eye, second outwards), the return beam can be

• *Ergonomics*: the need to come in close to the sensor may reduce the comfort of using the

• *Severe astigmatism*: people with visual impairment (astigmatism) are unable to focus the eye onto the point (a function comparable to measuring the focusing ability of the eye for an

• *High price*: it can be assumed that the price of the device, especially the retroviral optical device itself, will always be greater than, for example, the price of fingerprint or voice rec-

In the subsequent subsection, we discuss the iris and retinal recognition characteristics. Some of the characteristics already arise from the previous subsections where the principles of sens-

The acceptance for iris identification is on a middle level because there is no need for immediate interaction with the user. The user only has to stand in front of the device and look toward the sensor at a certain distance without rotating the head. The image capture and evaluation

ophthalmologist), thus avoiding the correct generation of the template.

**4. Characteristics of iris and retina recognition technology**

ing and processing these biometric features have been described.

the retina. All users need to be familiar with the system in order to gain confidence.

significantly weakened if the user's pupil is too small.

device more than other biometric methods.

**3.6. Limitations**

ognition devices.

**4.1. Acceptance**

time is about 2 s.

*4.1.1. Iris*

In connection with a device from EyeDentify, there were two main representations of the retinal image:


The retina template contains 96 fields of 4-bit contrast numbers from 96 scans of concentric circles in the time domain, that is, 96 × 4 = 48 bytes. Intensity in the time range can take values in the interval <−8.7>, normalizing for this layout—4 bits of intensive layout.

In the retina, when we talk about new research, the situation is relatively simple because the algorithms are searching the image for *bifurcations* and *crossings*, whose positions clearly define the person. The example is shown in **Figure 20**. Recognition becomes problematic when a stronger pathological phenomenon (e.g., a hemorrhage) occurs in the retina that affects the detection

**Figure 20.** Extracted features (bifurcations and crossings, incl. connection of macula and blind spot) in the retina.

and extraction of bifurcations and crossings. For biometric systems, it should be noted that their use also includes the disclosure of information about their own health status since, as mentioned earlier, a relatively large amount of information on human health can be read from the image of an iris, and that is especially so from a retina as well. It is therefore up to each of us on how much we will protect this private information and whether or not we will use the systems. However, if the manufacturer guarantees that the health information does not get stored, and only the unique features are stored (not the image), then we all may be more than happy to use the system.
