**3.1. Anatomy of the retina**

The retina is considered to be a part of the *central nervous system* (CNS). This is the only part of the CNS that can be observed noninvasively. It is a light-sensitive layer of cells located at the back of the eye with a thickness of 0.2–0.4 mm. It is responsible for sensing the light rays that hit it through the pupil and an eye lens that turns and inverts the image. The retina is a complex structure with several layers of neurons linked by synapses (**Figure 10**). The only neurons that react directly to light are *photoreceptors*. These are divided into two main types: *cones* and *rods*. In adults, the retina covers approximately 72% of the inner eye. The entire surface of the retina contains about 7 million cones and 75–150 million rods. This would compare the eye to a 157 MP camera. Rods are used to detect light and are capable of responding to the impact of one to two photons by providing black and white vision. Cones are used to detect colors and are divided into three types depending on which base color they are sensitive to (red, green, blue), but these are less sensitive to light intensity. In these cells, there is a phenomenon called *transduction* where the cascade of chemical and electrical phenomena changes into electrical impulses. These are then transmitted through the optic nerve to the central nervous system.

We can observe the two most distinctive points on an eye's retina. It is a *blind spot* (or an optical disc) and a *macula* (*yellow spot*). A blind spot is the point where the optic nerve enters the

**Figure 10.** Structure of the retina [11].

semi-automatic scanning to automatic, but the error rate of these systems is still relatively

• Images of the iris may be of poor quality, resulting in errors in registration, verification, or

• The iris can change over time, especially due to various illnesses. Changing the iris is possible in cataract surgery and illnesses such as *nystagmus* (shaking eyes) or *aniridia* (a completely missing iris). For some blind people, the iris may not be visible at all due to clouding

• The individual parts of the iris are related to the various internal organs of the human body, resulting in the possibility of misusing the scanned pattern to determine the health

Recognition by the retina is another option offered by the eye. Perhaps, the most complicated part of the entire retinal identification procedure is to obtain a good-quality eye image. Here, it is possible to inspire the principles of medical devices for the examination of an eye. It is also necessary to understand the function of the retina for human vision, its location, and the elements contained therein, according to which biometric identification can be carried out.

The retina is considered to be a part of the *central nervous system* (CNS). This is the only part of the CNS that can be observed noninvasively. It is a light-sensitive layer of cells located at the back of the eye with a thickness of 0.2–0.4 mm. It is responsible for sensing the light rays that hit it through the pupil and an eye lens that turns and inverts the image. The retina is a complex structure with several layers of neurons linked by synapses (**Figure 10**). The only neurons that react directly to light are *photoreceptors*. These are divided into two main types: *cones* and *rods*. In adults, the retina covers approximately 72% of the inner eye. The entire surface of the retina contains about 7 million cones and 75–150 million rods. This would compare the eye to a 157 MP camera. Rods are used to detect light and are capable of responding to the impact of one to two photons by providing black and white vision. Cones are used to detect colors and are divided into three types depending on which base color they are sensitive to (red, green, blue), but these are less sensitive to light intensity. In these cells, there is a phenomenon called *transduction* where the cascade of chemical and electrical phenomena changes into electrical impulses. These are then transmitted through the optic nerve to the

We can observe the two most distinctive points on an eye's retina. It is a *blind spot* (or an optical disc) and a *macula* (*yellow spot*). A blind spot is the point where the optic nerve enters the

of the person. This alternative medicine area is called *iridology* [10].

high.

identification.

16 Machine Learning and Biometrics

of the eyes.

**3. Recognition by retina**

**3.1. Anatomy of the retina**

central nervous system.

• Relatively high cost for high-performance systems.

eye, has a size of about 3 mm2 , and lacks all receptors. So, if the image falls into the blind spot, it will not be visible to a person. The brain often "guesses" how the image should look in order to fill this place. The existence of a blind spot can be tested as shown in **Figure 11**. If we close the left eye and observe the cross, then the black circle disappears at a certain distance from the image. This is precisely the moment when this image lands on a blind spot [5].

On the other hand, the *macula* (*yellow spot*) is referred to as the sharpest vision area, has a diameter of about 5 mm, and the cones predominate it (it is less sensitive to light). This area has the highest concentration of light-sensitive cells whose density is decreasing toward the edges. The center of the macula is *fovea*, which is the term describing receptor concentration and visual acuity. Our direct view is reflected in this area. Interestingly enough, the macula (yellow spot) is not really yellow, but slightly redder than the surrounding area. This attribute, however, was given by the fact that yellow appears after the death of an individual.

The retina is nourished by the *choroid*, which is a layer located between the retina and the sclera. It contains blood vessels and a pigment absorbing excess light. **Figure 12** shows how the retina is richly interwoven with nourishing vessels and nerves. It shows a similar apparatus to the brain, where the structure and venous tangle remain unchanged throughout life. The retina has two main sources of blood supply—the retinal artery and vessels. Larger blood flow to the retina is through the blood vessel that nourishes its outer layer with photoreceptors. Another blood supply is provided by the retinal artery, which primarily nourishes the inside of the retina. This artery usually has four major branches.

The retina located inside the eye is well protected from external influences. During life, the vessel pattern does not change and is therefore suitable for biometric purposes.

(bleeding or blood clots) appear in the retina; however, as mentioned earlier, potential damage (e.g., perforation or retinal detachment) or retinal disease is such a matter to go to ophthalmologists. Since our research group works with medical doctors, we process images or video sequences in which we look for pathological manifestations. At the present time, we focus on detecting and delimiting the exudates/druses and hemorrhages in the image, automatically detecting the position of the macula and blind spot. These are the reference points by which we determine the location of pathological findings. The worst area is the part called the fovea centralis, where the sharpest vision is located. Once this area is damaged, it has a very significant impact on our sight. An example of the detection of pathological findings is shown in **Figure 13**. We also deal with colleagues by detecting the quality of blood flow in the retina. There is still much to do in all areas of imaging and video processing for medical purposes, as input data are very different. For the time being (and probably still remaining so

Recognition of Eye Characteristics

19

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

Every part of the human body can be affected by a disease, whether it's curable or not. An incurable disease will be understood as a disability that cannot be surgically or otherwise removed without the biometric information (e.g., amputation) disappearing. The curable disease is removable with minimal consequences (e.g., inflammation, cuts). The retina can be affected by both types of these diseases. These diseases can significantly affect the course of recognition. If a disease disrupts the structure of the retina, it may cause erroneous evaluation

*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* 

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).

for a long time), the best diagnostic tool is a medical doctor.

*disease*. These diseases arise on the basis of inheritance.

or a complete rejection of the pattern.

*3.2.1. Macular degeneration*

**Figure 11.** Blind spot testing.

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

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 devices are used for the visual examination of the retina.

#### **3.2. Eye diseases**

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 (bleeding or blood clots) appear in the retina; however, as mentioned earlier, potential damage (e.g., perforation or retinal detachment) or retinal disease is such a matter to go to ophthalmologists. Since our research group works with medical doctors, we process images or video sequences in which we look for pathological manifestations. At the present time, we focus on detecting and delimiting the exudates/druses and hemorrhages in the image, automatically detecting the position of the macula and blind spot. These are the reference points by which we determine the location of pathological findings. The worst area is the part called the fovea centralis, where the sharpest vision is located. Once this area is damaged, it has a very significant impact on our sight. An example of the detection of pathological findings is shown in **Figure 13**. We also deal with colleagues by detecting the quality of blood flow in the retina. There is still much to do in all areas of imaging and video processing for medical purposes, as input data are very different. For the time being (and probably still remaining so for a long time), the best diagnostic tool is a medical doctor.

Every part of the human body can be affected by a disease, whether it's curable or not. An incurable disease will be understood as a disability that cannot be surgically or otherwise removed without the biometric information (e.g., amputation) disappearing. The curable disease is removable with minimal consequences (e.g., inflammation, cuts). The retina can be affected by both types of these diseases. These diseases can significantly affect the course of recognition. If a disease disrupts the structure of the retina, it may cause erroneous evaluation or a complete rejection of the pattern.
