**3. Recognition by retina**

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.

eye, has a size of about 3 mm2

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

individual.

, and lacks all receptors. So, if the image falls into the blind spot,

Recognition of Eye Characteristics

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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

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

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.

inside of the retina. This artery usually has four major branches.
