**1. Introduction**

Just like the parts of our body mentioned earlier, our eyes are completely unique and can be used for biometric purposes. There are two core parts in our eyes that even show relatively high biometric entropy. The first is the eye iris and the second is the eye retina that lies inside the eye that is not observable by the naked eye of the observer. Recognition based on these two biometric characteristics is a relatively new industry. The first patent for automated iris recognition is from 1994 [1].

The iris and the retina as elements inside the eye are very well protected against damage. The iris and retina patterns are unique to every person (this also applies to monozygotic twins), although the structure and iris color are genetically dependent:

• The *cornea* is located at the front of the eye. It is a transparent connective tissue that, along with the lens, allows the light to break into the eye. Its bad curvature causes astigmatism.


There are two scientific lines that deal with eye characteristics—those are *ophthalmology* and *biometrics*. *Ophthalmology* is a medical discipline aimed at analyzing and treating the health of the eye and its associated areas. The concept of *iridology* (the branch of alternative medicine that deals with the diagnosis of a person's health according to the image of the eye iris) is given only for completeness. In the field of *biometrics* (recognizing a person based on the unique biometric characteristics of the human body), the unique properties of the eye are not subject to change in time, and they are also so unique that it is possible to unequivocally identify two distinct individuals apart from each other in order to verify the identity of that person.

of pregnancy and forms during the first 2 years of life [4]. The basic structure remains unchanged during life, and even in twins, the iris is unique. The structure of the iris is shown in **Figure 2**.

Recognition of Eye Characteristics

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

The surface of the iris is quite complex. John Daugman described the 250 features that the iris

• *Crypts*: atrophy in front and stroma forming its typical drawing; these are the thinnest

• *Radial furrows*: a series of very fine razor-shaped nibs extending from the pupil to the

The light we perceive around us is an electromagnetic waving in the visible spectrum. Each of these waves has its own wavelength. We see the colors as different wavelengths of the visible

• 100–315 nm: absorbed predominantly in the cornea, the rest is dispersed in ventricular water.

contains. The most important of which for identification are the following:

• *Pigment spots*: random clusters of pigment on the surface of the iris.

spectrum, but the eye responds to other wavelengths as well [5]:

places of the iris.

**Figure 1.** Anatomy of the human eye [2].

**2.1. Influence of light on iris acquisition**

• 315–400 nm: absorbed in the lens.

collar.
