*3.2.1. Macular degeneration*

The retina acquires an image similar to a camera. The beam passing through the pupil appears in the focus of the lens on the retina, much like film. In medical practice, specialized optical

In the field of ophthalmology, the iris is not very interesting because when we neglect the extreme and very rare cases of a disease (e.g., irrigation or perforation of the iris, irritation of the iris), pigment changes occur often, which is not the result of a disease and has no effect on human health. The main focus is on ophthalmology in regard to examining the retina of the eye, of course taking into account the overall health of the eye (e.g., cataracts or increased intraocular pressure). In the retina, there is a relatively large line of diseases and damage that interest medical doctors, but they are detailed in an encyclopedia of ophthalmology with hundreds of pages (e.g., [12] (1638 pages) or [13] (2731 pages)). The large group is diabetes and age-related macular degeneration (ARMD). Occasionally, exudates/druses or hemorrhages

devices are used for the visual examination of the retina.

**Figure 12.** A snapshot of the retina taken by the fundus camera.

**3.2. Eye diseases**

**Figure 11.** Blind spot testing.

18 Machine Learning and Biometrics

*Macular degeneration* is a disease that occurs in 90% of cases with age, also known as agedrelated macular degeneration (ARMD). In the remaining percentage, macular degeneration occurs in children or young people in the form of *Best's macular degeneration* or *Stargardt's disease*. These diseases arise on the basis of inheritance.

In macular degeneration, the area of the retina, which forms at the center of the field of vision, is violated (**Figure 14**). As a result, a major disturbance of the central field of vision arises. In the center, the patient sees a gray shadow down to a black spot. The peripheral vision of the

**Figure 13.** Hemorrhage (left), detection of suspected areas (center), and highlighted hemorrhage (right).

**Figure 14.** Macular degeneration.

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

of infection). There are many forms of illness—nodal, ocular (see **Figure 16**), cerebral, gyneco-

Recognition of Eye Characteristics

21

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

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

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

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

logical. The other forms of toxoplasmosis are uncommon [16].

**Figure 15.** Non-proliferative (left) and proliferative diabetic retinopathy.

**3.3. Retinal examination tools**

cooperation.

scanned image.

**3.4. Histology of retinal recognition**
