The iris is the anterior part of the choroid of the eye. This is a very subtle peripheral component of it. She, the ciliary (ciliary) body and the choroid are the three main parts of the vascular tract, formed during the period from four to eight months of fetal development.
The iris is formed around the seventeenth week in the place where the edge of the so-called eye cup is the "imposition" of the mesoderm. 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 an internal muscle that will subsequently provide expansion. As a result of the harmonious and well-coordinated 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 main processes of formation of this system.
The human iris has no direct contact with the cornea. A small space remains between it and the outer wall - the anterior chamber, which is filled with aqueous (chamber) moisture.
The iris itself has the appearance of a round 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 light is around, the larger its diameter will be. Its average value is about three millimeters. At the same time, 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 dilator atrophy and fibrous changes in the sphincter occur over time.
The main properties of such an eye element 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 kind of lacy relief. The recesses of the slit-like type located in its connective tissue are called lacunae. Retreating one and a half millimeters parallel to the pupillary edge, mesentery (toothed roller) are located. They share the irisinto two sections: external (ciliary) and internal - pupillary. In the first zone, concentric furrows are defined. They are a direct consequence of the contraction and expansion of the iris as it moves.
The posterior part of the anterior part of the choroid is represented by a dilator with its pigment and boundary layers. The first at the pupillary edge forms a border, or fringe. The anterior iris includes the stroma of the iris and the outer boundary layer.
