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The shell of the eye. Outer shell of the eye

In the eyeball there are 2 poles: the back and the front. The distance between them is on average 24 mm. It is the largest size of the eyeball. The main mass of the latter is the inner core. This is transparent content, which is surrounded by three shells. It consists of watery liquid, crystalline lens and vitreous body. On all sides, the core of the eyeball is surrounded by the following three layers of the eye: fibrous (external), vascular (medium) and mesh (internal). Let's talk about each of them.

Outer sheath

The most durable is the outer shell of the eye, fibrous. It is thanks to her that the eyeball is able to maintain its shape.

Cornea

Cornea, or cornea - its smaller, anterior section. Its size is about 1/6 the size of the entire shell. The cornea in the eyeball is the most convex part of it. In its appearance it is a concave-convex, somewhat elongated lens, which is turned back by a concave surface. About 0.5 mm is the approximate thickness of the cornea. Its horizontal diameter is 11-12 mm. As for the vertical, its size is 10.5-11 mm.

Cornea - a transparent shell of the eye. It has in its composition a connective tissue stroma, as well as corneal bodies, which form its own substance. From the posterior and anterior surfaces, the posterior and anterior marginal plates adjoin the stroma. The latter is the basic substance of the cornea (mutated), the other is the derivative of the endothelium, which covers its posterior surface, and also lining the entire anterior chamber of the human eye. The multilayered epithelium covers the anterior surface of the cornea. It passes without sharp boundaries into the epithelium of the connective membrane. Due to the homogeneity of the tissue, as well as the lack of lymphatic and blood vessels, the cornea, unlike the next layer, which is the white shell of the eye, is transparent. Let us now turn to the description of the sclera.

Sclera

The white membrane of the eye is called the sclera. This is a larger, posterior part of the outer shell, which makes up about 1/6 of it. Sclera - the immediate continuation of the cornea. However, it is formed, unlike the latter, by fibers of connective tissue (dense) with an admixture of other fibers - elastic. The white envelope of the eye, moreover, is opaque. The sclera passes into the cornea gradually. A translucent bezel is on the border between them. It is called the edge of the cornea. Now you know what is the white shell of the eye. It is transparent only at the very beginning, near the cornea.

Departments of sclera

In the anterior part, the outer surface of the sclera is covered with conjunctiva. It's the mucous membrane of the eye. Otherwise it is called connective tissue. As for the rear department, here it covers only the endothelium. The inner surface of the sclera, which faces the choroid, also covers the endothelium. Not all along its sclera is the same in thickness. The thinnest area is the place where it is pierced by the fibers of the optic nerve that emerges from the eyeball. Here a lattice plate is formed. The sclera has the greatest thickness precisely in the circumference of the optic nerve. It is here from 1 to 1.5 mm. Then the thickness decreases, at the equator reaching 0.4-0.5 mm. Going to the area of muscle attachment, the sclera thickens again, its length here is about 0.6 mm. Not only the fibers of the optic nerve pass through it, but also the venous and arterial vessels, as well as the nerves. They form a row of holes in the sclera, which they call graduates of the sclera. Near the edge of the cornea, in the depth of the anterior part of the cornea, lies along the entire length of the sclera sinus, going circularly.

Vascular membrane

So, we briefly described the outer shell of the eye. We now turn to the characteristic of the vascular, which is also called the mean. It is divided into the following 3 unequal parts. The first of them is a large, posterior one, which lays about two thirds of the inner surface of the sclera. It is called the choroid. The second part - the middle, located on the border between the cornea and sclera. This is the ciliary body. And finally, the third part (smaller, front), translucent through the cornea, is called the iris, or iris.

Actually, the vascular membrane of the eye passes without sharp boundaries in the anterior parts into the ciliary body. The serrated edge of the wall can act as a boundary between them. Almost throughout the entire length of the vascular wall itself is only adjacent to the sclera, except for the spot area, as well as the area that corresponds to the optic nerve disk. The vascular membrane in the region of the latter has a visual aperture through which they exit to the latticed plate of the sclera of the optic nerve fiber. The outer surface of it is covered with the pigment and endothelial cells. It limits the circulatory capillary space together with the inner surface of the sclera.

The other layers of the envelope of interest are formed from the layer of large vessels that form the vascular plate. These are mainly veins, as well as arteries. Connective tissue elastic fibers, as well as pigment cells are located between them. A layer of medium vessels lies deeper than this layer. It is less pigmented. To it adjoins a network of small capillaries and vessels, forming a vascular capillary plate. It is especially developed in the area of the yellow spot. The structureless fibrous layer is the deepest zone of the vascular membrane proper. It is called the main plate. In the anterior part the vascular membrane thickens slightly and passes without sharp boundaries into the ciliary body.

Ciliary body

It is covered from the inner surface by the main plate, which is the continuation of the leaf. Leaf refers to the actual choroid. The ciliary body in its bulk consists of the ciliary muscle, as well as the stroma of the ciliary body. The latter is represented by a connective tissue, rich in pigment cells and loose, as well as a multitude of vessels.

The following parts are distinguished in the ciliary body: a ciliary circle, a ciliary ring and a ciliary muscle. The latter occupies its outer section and adjoins directly to the sclera. Ciliary muscle fibers formed a ciliary muscle. Among them are circular and meridional fibers. The latter are highly developed. They form a muscle, which serves to tighten the vascular membrane proper. From the sclera and the angle of the anterior chamber, its fibers begin. Going backwards, gradually they are lost in the choroid. This muscle, contracting, pulls forward the ciliary body (the posterior part of it) and the vascular wall proper (the front part). Thus, the tension of the ciliary band decreases.

Ciliary muscle

Circular fibers are involved in the formation of the circular muscle. Its reduction reduces the lumen of the ring, which is formed by the ciliary body. Thanks to this, the fixation to the equator of the lens of the ciliary band approaches. This causes relaxation of the girdle. In addition, the curvature of the lens increases. It is because of this that the circular part of the ciliary muscle is also called the muscle that compresses the lens.

Cilia

This is the posterior part of the ciliary body. In form it is arched, has an uneven surface. The ciliary circle continues without sharp boundaries in the actual choroid.

Ciliary Coronet

It takes the front part. It produces small folds that go radially. These ciliated folds pass anteriorly into the ciliated processes, which are about 70, and which hang freely in the area of the posterior chamber of the apple. The rounded edge is formed at the place where the transition to the ciliary rivet of the ciliary cup is observed. This is the place of attachment of the fixing lens of the ciliary band.

Iris

The anterior part is the iris, or iris. Unlike other departments, it does not directly attach to the fibrous membrane. Iris is an extension of the ciliary body (its anterior section). It is in the frontal plane and somewhat away from the cornea. A circular hole called the pupil is in its center. A ciliary edge is the opposite edge, which runs along the entire circumference of the iris. The latter consists of smooth muscles, vessels, connective tissue, as well as many nerve fibers. The pigment, which determines the "color" of the eye, has cells of the iris posterior surface.

Its smooth muscles are in two directions: radial and circular. The pupil is surrounded by a circular layer. It forms a muscle that narrows the pupil. The fibers, located radially, form the muscle, which expands it.

The anterior surface of the iris is slightly convex anteriorly. Accordingly, the posterior concave. On the anterior, in the circle of the pupil, there is an internal small iris ring (pupillary girdle). About 1 mm is its width. A small ring is bounded from the outside by an irregular denticle running circularly. It is called a small circle of the iris. The rest of its front surface is about 3-4 mm wide. It belongs to the outer large iris ring, or the ciliary part.

Retina

We have not considered all the shells of the eye. We presented fibrous and vascular. Which shell of the eye has not yet been examined? The answer is internal, mesh (it is also called retina). This shell is represented by nerve cells located in several layers. It lays the eye from the inside. The value of this shell of the eye is great. It is she who provides the person with sight, because objects are displayed on it. Then information about them is transmitted to the brain through the optic nerve. However, the retina does not all see the same. The structure of the shell of the eye is such that the macular is the largest visual ability.

Macula

It is the central part of the retina. We all heard from school that there are sticks and cones in the mesh shell . But in the macula there are only cones that are responsible for color vision. Without her, we could not distinguish between small details and read. In the macula, there are all conditions for registering light rays in the most detailed manner. The retina in this zone is thinner. Due to this light rays can get directly to the photosensitive cones. Vessels of the retina, capable of interfering with clear vision, are absent in the macula. Her cells are fed from the vasculature, which is deeper. Macula is the central part of the mesh shell of the eye, where the main number of cones (visual cells) is located.

What is inside the shells

Inside the membranes are located the front and back chambers (between the lens and the iris). Inside they are filled with liquid. Between them are the vitreous body and the lens. The latter is a biconvex lens in shape. The lens, like the cornea, refracts and transmits rays of light. Due to this, the image is focused on the retina. Vitreous body by the consistency of jelly. The ocular fundus is separated from the lens by means of it.

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