**2.2 Anatomy of the retina**

The retina is located at the back of the eye and is the only part of the central nervous system that is non-invasively observable. It is responsible for light rays sensing and vision at all. It is a very thin light-sensitive layer that is transparent. Retinal cameras capture deeper layers of the eye behind the retinal layer. Its thickness is 0.2-0.4 mm and contains two types of light-sensitive cells, rods and cones. The rods, which are approximately 75 to 150 million [3, 4], are used for more sensitive vision in low light. However, the rods only send information to the brain in the grayscale. On the contrary, the cones perceive incident light rays in color, but they need more light to function than rods. There are approximately 7 million of them in one eye and are divided according to the perception of colors red, green, and blue. The peripheral part of the retina is rod-dominated, whereas the yellow spot is conedominated. Low density of rods in the yellow spot makes it less sensitive to the light. Retina would be compared with 157-megapixel camera [3, 4].

**79**

**Figure 2.** *Retinal image [5].*

*Retina Recognition Using Crossings and Bifurcations DOI: http://dx.doi.org/10.5772/intechopen.96142*

about 3 mm2

**2.3 Retinal vasculature**

acquisition is not possible.

inside of it.

Two main parts of the retina are shown in **Figure 2**. It is a blind spot (optic disk) and a macula (yellow spot). Optic disk is a circular area with an average surface of

from the retinal neurons, form the optic nerve, the central retinal artery comes into the retina and the retinal vein leaves the retina. The color of a normal optic disk varies from orange to pink. The optic disk is known as a "blind spot" since it does not contain photoreceptors, i.e., rods and cones. Corresponding parts of the visual field are not visible to a person. However, thanks to the ability of the brain to ignore or interpolate missing information from the other eye, we usually do not notice the blind spot. Opposite to the optic disk macula (yellow spot) is the sharpest vision area with a diameter of around 5 mm. The highest concentration of cones on the macula makes it responsible for the perception of colors. Fovea is located in the center of the macula with the densest concentration of photoreceptors in the eye. The image of the object falling on the macula (yellow spot) is reflected in the fovea.

The structure of retinal vessels is much like the brain and remains unchanged throughout life. Two main sources of blood supplying the retina are the retinal artery and the vessels. The blood vessels nourish the retina's outer layer with photoreceptors. Meanwhile, four major branches of the retinal artery called terminal arterioles, provide blood supply to the retina, nourishing in the first place the

One type of retinal scanners is the fundus camera, which is a specialized low power microscope with an attached camera. **Figure 3** shows the fundus camera used in the biometric laboratory of Faculty of Information Technology (FIT) at Brno University of Technology (BUT) in Czech Republic (CZ). No matter which kind of retinal scanners is used, without user's conscious cooperation the retinal image

Blood vessels coming out from the blind spot and make a tree shape on the surface of the retina (shown in **Figure 2**). This tree shape hardly ever changes over the lifetime of an individual except due to some severe eye diseases such as hard glaucoma and cataracts. It is not affected by external environment, since the retina is not an external organ such as a fingerprint [8, 9]. Moreover, it differs from person to person due to many factors such as the thickness of vessels, the distance from

where ganglion cells, i.e., projection neurons transferring information

**Figure 1.** *Anatomy of an eye [1].*

Two main parts of the retina are shown in **Figure 2**. It is a blind spot (optic disk) and a macula (yellow spot). Optic disk is a circular area with an average surface of about 3 mm2 where ganglion cells, i.e., projection neurons transferring information from the retinal neurons, form the optic nerve, the central retinal artery comes into the retina and the retinal vein leaves the retina. The color of a normal optic disk varies from orange to pink. The optic disk is known as a "blind spot" since it does not contain photoreceptors, i.e., rods and cones. Corresponding parts of the visual field are not visible to a person. However, thanks to the ability of the brain to ignore or interpolate missing information from the other eye, we usually do not notice the blind spot. Opposite to the optic disk macula (yellow spot) is the sharpest vision area with a diameter of around 5 mm. The highest concentration of cones on the macula makes it responsible for the perception of colors. Fovea is located in the center of the macula with the densest concentration of photoreceptors in the eye. The image of the object falling on the macula (yellow spot) is reflected in the fovea.
