The iris is the front of the choroid . This is a very subtle peripheral component. She, the ciliary (ciliary) body and the choroid are the three main parts of the vascular tract, formed in the period from four to eight months of fetal development.
The iris forms around the seventeenth week at the place where the mesoderm is “superimposed” on the edge of the so-called eye glass. By the fifth month, the iris sphincter is formed - the muscle responsible for reducing the size of the pupil. A little later a dilator appears. This is the internal muscle, which will subsequently provide expansion. As a result of harmonious and harmonious interaction of the sphincter and dilator, the iris of the eye performs the function of a diaphragm, which effectively regulates the flow of penetrating light rays. By the sixth month, the posterior pigment epithelial tissue is fully formed . This completes the basic processes of the formation of this system.
The iris of the human eye does not have direct direct contact with the cornea. Between it and the outer wall there is a small space - the anterior chamber, which is filled with aqueous (chamber) moisture.
The iris itself has the form of a rounded plate with a diameter of about twelve millimeters and a perimeter of about thirty-eight millimeters. In its center is a round hole through which light penetrates - the pupil. It is he who serves to regulate the volume of rays penetrating the eye. The size of the pupil depends on the degree of illumination. The smaller the world around, the larger its diameter. Its average value is about three millimeters. Moreover, in young people, the diameter of the pupil, as a rule, is slightly larger than in the elderly. This is due to the fact that over time, atrophy of the dilator and fibrous changes in the sphincter occur.
The main properties of such an element of the eye as the iris are color, pattern, state of the pupil opening and location relative to other structures of the eye. All of them are due to certain anatomical characteristics of its structure.
The front layer of the iris has a radial striation, which gives it a peculiar lace relief. Slit-like depressions located in its connective tissue are called lacunae. Retreating one and a half millimeters parallel to the pupillary edge, there are mesenteries (a gear roller). They divide the iris into two sections: the outer (ciliary) and the inner pupil. In the first zone, concentric furrows are defined. They are a direct consequence of the contraction and expansion of the iris during its movement.
The posterior part of the anterior part of the choroid is represented by a dilator with its pigment and border layers. The first at the pupil edge forms a border, or fringe. The anterior section of the iris includes the stroma of the iris and the outer boundary layer.