**3.3. Retinal examination tools**

macula remains intact. Macular degeneration can occur in two forms of dry (*atrophic*) and wet (*exudative*). The most common symptoms include a blurred gray or a black spot at the center of the field of vision (the so-called *central scotoma*). The affected person sees deformed straight lines, blurred letters, or inappropriate shapes of different objects. It also affects color vision,

*Diabetic retinopathy* (DR) is an inflammatory disease of the retina. It arises as a result of the total affection of blood vessels in diabetes mellitus. Wrongly diagnosed diabetes affects small catheters that clog in the eyes, causing blood circulation to slow. The second way the retina is affected is that the vessels "leak" and the fluid escapes and causes the retina to swell. Insufficient blood circulation and swelling of the retina destroy vision. The eye tries to remedy the situation by growing new blood vessels (*neovascularization*), but they are poor and harmful, they crack, they can bleed in the eye (*hemophthalmos*), and they can cause traction detachment of the retina. Diabetic retinopathy has two forms: *non-proliferative* and *proliferative*

*Toxoplasmosis* is a disease that ranks among *zoonoses*, which is transmissible from animals to humans. It occurs all over the world. In European countries, anti-toxoplasmosis antibodies are produced by 10–60% of the population depending on dietary habits. In the Czech Republic, *seropositivity* (the presence of antibodies in the blood) is around 20–40%. Diseases are most often manifested by elevated temperatures, flu-like conditions, headaches, fatigue, or swollen lymph nodes. An acute infection may sometimes go into a chronic stage, but the infection is often unnoticed and is only recognized by the finding of specific anti-toxoplasmic antibodies in the blood, which may persist in low levels throughout their lives (the latent form

which seems to have faded. Side vision remains sharp on one or both eyes [14].

*3.2.2. Diabetic retinopathy*

**Figure 14.** Macular degeneration.

20 Machine Learning and Biometrics

[15] (**Figure 15**).

*3.2.3. Toxoplasmosis*

The most commonly used device for examining the retina is a *direct ophthalmoscope*. When using an ophthalmoscope, the patient's eye is examined from a distance of several centimeters through the pupil. Several types of ophthalmoscopes are currently known but the principle is essentially the same: the eye of the investigated and the investigator is in one axis, and the retina is illuminated by a light source from a semipermeable mirror or a mirror with a hole located in the observation axis at an angle of 45° [17]. The disadvantage of a direct ophthalmoscope is a relatively small area of investigation, the need for skill when handling, and patient cooperation.

For a more thorough examination of the eye background, the so-called *fundus camera*, which is currently most likely to have the greatest importance in examining the retina, is used. It allows color photography to make up virtually the entire surface of the retina, as can be seen in **Figure 12**. The optical principle of this device is based on the so-called indirect ophthalmoscopy [17]. Fundus cameras are equipped with a white light source to illuminate the retina and then scan it with a charge-coupled device (CCD) sensor. Some types can also find the center of the retina and automatically focus it using a frequency analysis of the scanned image.

#### **3.4. Histology of retinal recognition**

In 1935, ophthalmologists *Carleton Simon* and *Isidore Goldstein* discovered eye diseases where the image of the bloodstream in two individuals in the retina was unique for each individual. Subsequently, they published a journal article on the use of vein image in the retina as a unique pattern for identification [18]. Their research was supported by Dr. Paul Tower, who in 1955 published an article on studying monozygotic twins [19]. He discovered that retinal

**3.5. Technology and principles**

The functional principle of the device can be divided into three non-trivial subsystems [20]:

Recognition of Eye Characteristics

23

http://dx.doi.org/10.5772/intechopen.76026

• *Image, signal acquisition, and processing*: the optical system and the camera must be capable

• *Comparison*: a program on a device or a computer that extracts key features from a scanned

• *Representation*: each retinal image must be represented in such a way that it can be quickly

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].

of capturing a digital image of the retina suitable for processing.

image and compares it to a database of patterns.

compared or stored in the database.

*3.5.1. Sensing optical system*

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

vessel patterns show the least resemblance to all the other patterns examined. At that time, identification of the vessel's retina was a timeless thought.

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 not appear on the market for several years.

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

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 when the eye is irradiated.

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 chosen as the most appropriate.

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 with the data stored in the database.

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 domain to accelerate recognition.
