Ciliary (ciliary) body

The ciliated, or ciliary, body (corpus ciliare) is the middle thickened part of the vascular tract of the eye that produces the production of intraocular fluid. The ciliary body gives a support to the lens and provides an accommodation mechanism, in addition, it is the thermal eye collector

Under normal conditions, the ciliary body, located under the sclera in the middle between the iris and the choroid, is not available for inspection: it is hidden behind the iris. The area of the ciliary body is projected on the sclera in the form of a ring 6-7 mm wide around the cornea. On the outside, this ring is slightly wider than with the nose.

The ciliary body has a rather complex structure. If you cut your eye along the equator and look from the inside to the front, you will clearly see the inner surface of the ciliary body in the form of two round belts of dark color. In the center, surrounding the crystalline lens, a folded ciliary crown with a width of 2 mm rises (corona ciliaris). Around it is a ciliary ring, or a flat part of the ciliary body, 4 mm wide. It goes to the equator and ends with a dentate line. The projection of this line on the sclera is in the area of attachment of the rectus muscles of the eye.

The ring of the ciliary crown consists of 70-80 large processes oriented radially in the direction of the lens. Macroscopically, they look like cilia (cilia), hence the name of this part of the vascular tract - "ciliary, or ciliary, body." The apexes of the processes are lighter than the general background, the height is less than 1 mm. Between them there are tubercles of small processes. The space between the equator of the lens and the process part of the ciliary body is only 0.5-0.8 mm. It is occupied by a ligament supporting the lens, which is called a ciliary band, or a zinnic ligament. It is the support for the lens and consists of the finest filaments coming from the anterior and posterior capsules of the lens in the region of the equator and attached to the processes of the ciliary body. However, the main ciliated processes are only part of the ciliary band, while the main fiber network passes between the processes and is fixed all over the ciliary body, including its flat part.

The delicate structure of the ciliated body is usually studied on the meridional section, which shows the transition of the iris to the ciliary body, which has the form of a triangle. The wide base of this triangle is located at the front and represents the process part of the ciliary body, and the narrow apex is its flat part that passes into the posterior section of the vascular tract. As in the iris, the ciliary body exudes an external vascular-muscular layer, which is of mesodermal origin, and an internal retinal or neuroectodermal layer.

The outer mesodermal layer consists of four parts:

• suprachorioidea. This is the capillary space between the sclera and the choroid. It can expand due to the accumulation of blood or edematous fluid in the eye pathology;
• accommodative, or ciliary, muscle. It occupies a considerable volume and gives the ciliary body a characteristic triangular shape;
• vascular layer with ciliary processes;
• the elastic membrane of Bruch.

The inner retinal layer is a continuation of the optically inactive retina, reduced to two layers of epithelium - the outer pigment and internal pigmentless membrane covered with a border membrane.

To understand the functions of the ciliary body, the structure of the muscular and vascular parts of the external mesodermal layer is of particular importance.

The accommodating muscle is located in the anterior part of the ciliary body. It includes three main portions of smooth muscle fibers: meridional, radial and circular. Meridional fibers (Brueck muscle) abut the sclera and attach to it at the inner part of the limb. When the muscle contraction occurs, the ciliary body moves forward. Radial fibers (Ivanov's muscle) fan out from the scleral spur to the ciliary tract, reaching the flat part of the ciliary body. Thin bundles of circular muscle fibers (Müller's muscle) are located in the upper part of the muscular triangle, form a closed ring and act as a sphincter when contracted.

The mechanism of contraction and relaxation of the muscular apparatus lies at the basis of the accommodative function of the ciliary body. With the reduction of all portions of multidirectional muscles, there is an effect of a general decrease in the length of the accommodative muscle along the meridian (pulled up anteriorly) and increasing its width in the direction of the lens. The ciliary band narrows around the lens and approaches it. Zinnova ligament relaxes. The lens, due to its elasticity, tends to change the disk form to a spherical shape, which leads to an increase in its refraction.

The vascular part of the ciliary body is located inward from the muscular layer and is formed from the large arterial circle of the iris located at its root. It is represented by a dense weave of blood vessels. Blood carries not only nutrients, but also heat. In the open front section of the eyeball, the ciliary body and the iris are the heat collector.

The cilia are filled with vessels. These are unusually wide capillaries: if the erythrocytes pass through the retinal capillaries, only changing their shape, then up to 4-5 erythrocytes can be placed in the lumen of the capillaries of the ciliated processes. The vessels are located directly under the epithelial layer. This structure of the middle part of the vascular tract of the eye provides the function of secretion of the intraocular fluid, which is an ultrafiltrate of blood plasma. The intraocular fluid creates the necessary conditions for the functioning of all intraocular tissues, provides the avascular formations (cornea, lens, vitreous body), maintains their thermal regime, maintains the tone of the eye. With a significant decrease in the secretory function of the ciliary body, intraocular pressure decreases and atrophy of the eyeball occurs.

The unique structure of the vasculature of the ciliary body described above is fraught with negative properties. In the wide convoluted blood vessels the blood flow is slowed down, as a result of it conditions for the settling of pathogens of infection are created. As a consequence, with any infectious diseases in the body, inflammation in the iris and ciliary body can develop.

The ciliary body is innervated by the branches of the oculomotor nerve (parasympathetic nerve fibers), the branches of the trigeminal nerve and sympathetic fibers from the interweaving of the internal carotid artery. Inflammatory phenomena in the ciliary body are accompanied by severe pain due to rich innervation of the branches of the trigeminal nerve. On the outer surface of the ciliary body there is a plexus of nerve fibers - a ciliary node, from which branches branch to the iris, cornea and ciliary muscle. The anatomical feature of the innervation of the ciliary muscle is the individual supply of each smooth muscle cell with a separate nerve end. This is not in any other muscle of the human body. The expediency of such a rich innervation is mainly due to the need to ensure the implementation of complex centrally controlled functions.

Functions of the ciliary body:

• support for the lens;
• participation in the act of accommodation;
• production of intraocular fluid;
• thermal collector of anterior segment of eye.

[1], [2], [3], [4], [5], [6]