Eye diseases. Vascular tract of the eye (most important)

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Eye diseases. Vascular tract of the eye (most important)

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4. Vascular tract of the eye

The vascular tract, consisting of the iris, ciliary body and choroid, is located medially from the outer shell of the eye. It is separated from the latter by the suprachoroidal space, which is formed in the first months of a child's life.

The iris (anterior part of the vascular tract) forms a vertically standing diaphragm with a hole in the center of the pupil that regulates the amount of light entering the retina. The vascular network of the iris is formed by branches of the posterior long and anterior ciliary arteries and has two circles of blood circulation.

The iris can have a different color: from blue to black. Its color depends on the amount of melanin pigment contained in it: the more pigment in the stroma, the darker the iris; in the absence or small amount of pigment, this shell has a blue or gray color. In children, there is little pigment in the iris, so in newborns and children of the first year of life, it is bluish-gray. The color of the iris is formed by the age of ten and twelve. On its front surface, two parts can be distinguished: a narrow one, located near the pupil (the so-called pupillary), and a wide one, bordering on the ciliary body (ciliary). The boundary between them is the pulmonary circulation of the iris. There are two muscles in the iris that are antagonists. One is placed in the pupillary region, its fibers are located concentrically to the pupil, with their contraction the pupil narrows. Another muscle is represented by radially running muscle fibers in the ciliary part, with the contraction of which the pupil expands.

The ciliary body consists of a flat and thickened coronal parts. The thickened coronal part consists of 70 to 80 ciliary processes, each of which has vessels and nerves. The ciliary, or accommodative, muscle is located in the ciliary body. The ciliary body is dark in color and covered with retinal pigment epithelium. Zinn ligaments of the lens are woven into it in the interprocesses. The ciliary body is involved in the formation of intraocular fluid that nourishes the avascular structures of the eye. The vessels of the ciliary body depart from the large arterial circle of the iris, which is formed from the posterior long and anterior ciliary arteries. Sensitive innervation is carried out by long ciliary fibers, motor parasympathetic fibers of the oculomotor nerve and sympathetic branches.

The choroid, or the choroid itself, is composed mainly of short posterior ciliary vessels. In it, with age, the number of pigment cells of chromatophores increases, due to which the choroid forms a dark chamber that prevents the reflection of rays entering through the pupil. The basis of the choroid is a thin connective tissue stroma with elastic fibers. Due to the fact that the choriocapillary layer of the choroid is attached to the retinal pigment epithelium, a photochemical process is carried out in the latter.

Author: Shilnikov L.V.

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