Choroid (choroid) - structure and function. The middle layer of the eye What does the choroid of the eyeball do
Eye shell
The eyeball has three membranes - outer fibrous, middle vascular, and inner, which is called the retina. All three membranes surround the nucleus of the eye. (see appendix 1)
The fibrous membrane consists of two parts - the sclera and the cornea.
The sclera is also called the white of the eye or the tunica albuginea, it is dense white, consists of connective tissue. This shell makes up the majority of the eyeball. The sclera serves as the frame of the eye and performs a protective function. In the posterior parts of the sclera, it has a thinning lattice plate through which the optic nerve leaves the eyeball. In the anterior parts of the optic globe, the sclera passes into the cornea. The place of this transition is called the limb. In newborns, the sclera is thinner than in adults, so the eyes of young animals have a bluish tint.
The cornea is a transparent tissue located in the front of the eye. The cornea rises slightly above the level of the sphere of the eyeball, since the radius of its curvature is less than the radius of the sclera. Normally, the cornea is scleral-shaped. There are a lot of sensitive nerve endings in the cornea, so when acute diseases the cornea has severe lacrimation, photophobia. The cornea has no blood vessels, and the metabolism in it occurs due to the moisture of the anterior chamber and lacrimal fluid. Violation of the transparency of the cornea leads to a decrease in visual acuity.
The choroid is the second membrane of the eye, it is also called the vascular tract. This membrane is made up of a network of blood vessels. Conventionally, for a better understanding of internal processes, it is divided into three parts.
The first part is the choroid itself. It has the largest area and lines the two posterior thirds of the sclera from the inside. It serves for the metabolism of the third shell - the retina.
Further, in front is the second, thicker part of the choroid - the ciliary (ciliary) body. The ciliary body has the form of a ring, located around the limbus. The ciliary body is composed of muscle fibers and many ciliary processes. The fibers of the zinc ligament begin from the ciliary processes. With the other end, the Zinn ligaments are woven into the lens capsule. In the ciliary processes, the formation of intraocular fluid occurs. Intraocular fluid is involved in the metabolism of those structures of the eye that do not have their own vessels.
The muscles of the ciliary body go in different directions and attach to the sclera. When these muscles contract ciliary body pulls forward a little, which weakens the tension of the zinn ligaments. This releases the tension on the lens capsule and allows the lens to bulge. Changing the curvature of the lens is necessary to clearly distinguish the details of objects at different distances from the eye, that is, for the process of accommodation.
The third part of the choroid is the iris, or iris. The color of the eyes depends on the amount of pigments in the iris. The blue-eyed have little pigment, the brown-eyed have a lot. Therefore, the more pigment, the darker the eye. Animals with a reduced pigment content, both in the eyes and in the coat, are called albinos. The iris is a circular membrane with a hole in the center, consisting of a network of blood vessels and muscles. The muscles of the iris are located radially and concentrically. When concentric muscles contract, the pupil contracts. If the radial muscles contract, the pupil expands. The size of the pupil depends on the amount of light falling on the eye, age and other reasons.
The third, inner shell of the eyeball is the retina. She, in the form of a thick film, lines the entire back of the eyeball. Retinal nutrition occurs through the vessels that enter the area optic nerve, and then branch out and cover the entire surface of the reticular membrane. It is on this shell that the light reflected by the objects of our world falls. In the retina, the rays are converted into a nerve signal. The retina consists of 3 types of neurons, each of which forms an independent layer. The first is represented by the receptor neuroepithelium (rods and cones and their nuclei), the second - by bipolar neurons, the third - by ganglion cells. There are synapses between the first and second, second and third layers of neurons.
In accordance with the location, structure and function in the retina, two parts are distinguished: the visual, lining the back from the inside, most of the wall of the eyeball, and the anterior pigment, covering the ciliary body and the iris from the inside.
The visual part contains photoreceptor, primary sensory nerve cells. Photoreceptors are of two types - rods and cones. Where the optic nerve forms on the retina, there are no sensitive cells. This area is called a blind spot. Each photoreceptor cell consists of an outer and an inner segment; the outer segment of the rod is thin, long, cylindrical; the cone has a short, conical segment.
The light-sensitive leaf of the retina contains several types of nerve cells and one type of glial cells. The nucleated regions of all cells form three layers, and the zones of synoptic contacts of cells form two reticular layers. Thus, in the visual part of the retina, the following layers are distinguished, counting from the surface in contact with the choroid: a layer of pigment epithelial cells, a layer of rods and cones, an outer boundary membrane, an outer nuclear layer, an outer reticular layer, an inner nuclear layer, an inner reticular layer, ganglion layer, a layer of nerve fibers and an internal boundary membrane. (Kvinikhidze G.S. 1985). (see appendix 2)
The pigment epithelium is anatomically closely associated with the choroid. The pigment layer of the retina contains a black pigment called melanin, which is actively involved in providing clear vision. The pigment, absorbing light, prevents it from being reflected from the walls and reaching other receptor cells. In addition, the pigment layer contains a large amount of vitamin A, which is involved in the synthesis of visual pigments in the outer segments of rods and cones, where it can be easily transferred. The pigment epithelium is involved in the act of vision, since it forms and contains visual substances.
The rods and cones layer consists of the outer segments of photoreceptor cells surrounded by processes of pigment cells. Rods and cones are located in a matrix containing glycosaminoglycans and glycoproteins. There are two types of photoreceptor cells, differing in the shape of the outer segment, but also in the number, distribution in the retina, ultrastructural organization, and also in the form of synaptic connection with the processes of deeper retinal elements - bipolar and horizontal neurons.
The retina of diurnal animals and birds (diurnal rodents, chickens, pigeons) contains almost exclusively cones; in the retina of nocturnal birds (owl, etc.), visual cells are mainly represented by rods.
The inner segment contains the main cellular organelles: the accumulation of mitochondria, polysomes, elements of the endoplasmic reticulum, the Golgi complex.
The rods are dispersed mainly along the periphery of the retina. They are characterized by increased photosensitivity in low light conditions, they provide night and peripheral vision.
The cones are located in the central part of the retina. They can distinguish the smallest details and color, but for this they need a lot of light. Therefore, in the dark, the flowers seem the same. The cones fill a special area of \u200b\u200bthe retina - the macula. In the center of the macula is the central fossa, which is responsible for the greatest visual acuity.
However, it is not always possible to distinguish cones from rods by the shape of the outer segment. So, the cones of the central fossa - the places of the best perception of visual stimuli - have a thin outer segment elongated in length, and resemble a rod.
The inner segments of rods and cones also differ in shape and size; at the cone, it is much thicker. The inner segment contains the main cellular organelles: the accumulation of mitochondria, polysomes, elements of the endoplasmic reticulum, the Golgi complex. The cones in the inner segment have a section consisting of an accumulation of tightly adjacent mitochondria with an ellipsoid located in the center of this accumulation. Both segments are connected by a so-called leg.
There is a kind of "specialization" among photoreceptors. Some photoreceptors signal only about the presence of a black vertical line on a light background, others about a black horizontal line, and still others about the presence of a line tilted at a certain angle. There are groups of cells that report outlines, but only those that are oriented in a certain way. There are also types of cells that are responsible for the perception of movement in a specific direction, cells that perceive color, shape, etc. The retina is extremely complex, so a huge amount of information is processed in milliseconds.
The human eye is a unique optics that has several shell layers in its structure. He, like a lens, allows you to see the world in three-dimensional, and in color.
The structure of the middle membrane of the eye
The middle is the choroidThe choroid is the middle section of the eye membrane, which is adjacent, on the one hand, to the retina and on the other to the sclera. It has another name for choroid. In turn, the choroid consists of:
- iris - the front of the shell;
- ciliary or ciliary body;
- the choroid itself (choroid), most of which consists of a large number of large vessels and small capillaries.
The iris gives color to the eyes thanks to the pigments. The pupil is located in the center of the iris. Under strong magnification, a lace pattern from the vessels is visible on the iris.
They form a single pattern for each person. By the iris of the eyes, you can recognize a predisposition to disease and the presence of diseases at the moment.
The functions of the iris are as follows:
- Closing the eye from excess light is accomplished with the help of two muscles that constrict and dilate the pupil.
- A diaphragm separation between the anterior and posterior parts of the eye, holding vitreous.
- Carries out the outflow of intraocular fluid.
- Carries out thermoregulation.
The body is ciliary or ciliary, this is the middle part of the eye membrane. It holds the lens so that it is not pulled to the side, helps the adaptation of the visual organ when examining objects at different distances from the eye.
The body is activated to produce intraocular fluid. Just like the iris, it is involved in thermoregulation of the anterior region of the eye organ.
The shell has a five-layer look. Small capillaries of the membrane adjoin the retina; a thin Bruch's membrane passes between the retina and the vessels. The membrane implements the exchange of food between the membrane and the retina.
The main function of the choroid is to organize the nutrition of the layers of the outer part of the membrane and the output of metabolic products from adjacent sections into the blood.
Middle membrane of the eye, pathology, treatment
The iris determines the color of the eyes Eye diseases can occur at any time in our lives, the risk of their occurrence increases with age. To determine the degree of damage, eye pathology, it is necessary to conduct a high-quality complete diagnosis and periodic preventive examinations.
The survey is applied:
- ophthalmoscope;
- angiography determines the state of the blood vessels, reveals damage to Bruch's membrane.
- ultrasound examination.
Pathology of the middle membrane of the eye
Changes in the middle membrane are congenital and acquired. A congenital pathology is the absence of a choroid in a certain area. The acquired ones include:
- Dystrophic lesions of the choroid.
- Choriodea inflammation can coexist with damage to the retina.
- Detachment of the membrane that appears during surges in intraocular pressure, for example, during glaucoma surgery.
- Rupture and hemorrhage of the membrane with eye injury.
- Nevus (birthmark or birthmark) of the choroid.
- Neoplasms of a benign and malignant nature.
- Iridocyclitis is inflammatory process in the iris and ciliary body.
Treatment
Middle shell suffers from bad habits The inflammatory process of the choroid is treated with medication:
- anesthetics;
- antihistamines;
- anti-inflammatory drugs;
- vaso-strengthening;
- antimicrobial and antiviral;
- neurotropic;
- absorbable;
- Carry out laser treatment, surgical intervention.
- When iridocyclitis is also used drug treatment, electropharesis, UHF, ultrasound, magnetotherapy.
Prevention
Of great importance is the prevention of diseases of the eye and choroid, including. Regular consumption of foods rich in trace elements such as zinc, selenium, copper.
Consumption of a sufficient amount of vitamins B, C, A, E. Strengthening the immune system. Reducing the use of coffee, strong tea, sugar, smoking cessation and alcohol.
To deal with possible diseases, complications of the visual organ, you need to be literate in this area.
Anatomy and physiology of the eyeball
The eyeball with its adnexa is the receiving part of the visual analyzer. The eyeball has a spherical shape, consists of 3 membranes and intraocular transparent media. These membranes surround the internal cavities (chambers) of the eye, filled with transparent aqueous humor (intraocular fluid), and the transparent internal refractive media of the eye (lens and vitreous).
Outer shell of the eye
This fibrous capsule provides eye turgor, protects it from external influences and serves as a place of attachment oculomotor muscles... Vessels and nerves pass through it. This membrane consists of two sections: anterior - transparent cornea, posterior - opaque sclera. The junction of the cornea into the sclera is called the edge of the cornea or limbus.
The cornea is the transparent part of the fibrous capsule, which is the refractive medium when light rays enter the eye. Its refractive power is 40 diopters (diopters). There are many nerve endings in it; any speck, when it gets into the eye, causes pain. The cornea itself has good permeability, is covered with epithelium and normally has no blood vessels.
The sclera is the opaque portion of the fibrous capsule. Consists of collagen and elastic fibers. Normally it is white or blue-white. Sensory innervation of the fibrous capsule is carried out by the trigeminal nerve.
It is a choroid, its pattern is visible only with biomicro - and ophthalmoscopy. This shell consists of 3 sections:
1st (front) section - iris. It is located behind the cornea, between them there is a space - the anterior chamber of the eye, filled with aqueous humor. The iris is clearly visible from the outside. It is a pigmented round plate with a central hole (pupil). The color of the eyes depends on its color. The diameter of the pupil depends on the level of illumination and the work of two antagonistic muscles (constricting and dilating the pupil).
2nd (middle) department - ciliary body.It iis the middle part of the choroid, a continuation of the iris. Zinn's ligaments extend from its processes, which support the lens. Depending on the condition of the ciliary muscle, these ligaments can stretch or contract, changing the curvature of the lens and its refractive power. The ability of the eye to see near and far equally well depends on the refractive power of the lens. Adjusting the eye to see clearly and best at any distance is called accommodation. The ciliary body produces and filters aqueous humor, thereby regulating intraocular pressure, and due to the work of the ciliary muscle, it provides accommodation.
3rd (back) section - the choroid itself . It is located between the sclera and the retina, consists of vessels of different diameters and supplies blood to the retina. Due to the absence of sensitive nerve endings in the choroid, its inflammation, injuries and tumors are painless!
Inner lining of the eye (retina)
It is a specialized brain tissue brought out to the periphery. Vision is carried out with the help of the retina. In terms of its architectonics, the retina is similar to the brain. This thin, transparent membrane lines the fundus and connects with other membranes of the eye in only two places: at the dentate edge of the ciliary body and around the optic nerve head. For the rest of the length, the retina adheres tightly to the choroid, which is facilitated mainly by the pressure of the vitreous body and intraocular pressure, therefore, with a decrease in intraocular pressure, the retina can flake off. The distribution density of light-sensitive elements (photoreceptors) in different parts of the retina is not the same. The most important spot on the retina is the retinal spot - this is the region of best perception for visual sensations (a large congestion of cones). In the central part of the fundus there is an optic disc. It is visible in the fundus through the transparent structures of the eye. The area of \u200b\u200bthe optic nerve head does not contain photoreceptors (rods and cones) and is a "blind" area of \u200b\u200bthe fundus (blind spot). The optic nerve passes into the orbit through the canal of the optic nerve, in the cranial cavity in the area of \u200b\u200bthe optic chiasm, a partial intersection of its fibers occurs. The cortical representation of the visual analyzer is located in the occipital lobe of the brain.
Transparent intraocular medianecessary for the transmission of light rays to the retina and their refraction. These include the chambers of the eye, the lens, the vitreous humor, and aqueous humor.
Anterior chamber of the eye. It is located between the cornea and the iris. In the corner of the anterior chamber (iris-corneal angle) there is a drainage system of the eye (helmet canal), through which aqueous humor flows into the venous network of the eye. Outflow disturbance leads to an increase in intraocular pressure and the development of glaucoma.
Rear chamber of the eye... In front, it is limited by the posterior surface of the iris and the ciliary body, and the capsule of the lens is located behind.
Lens . This is an intraocular lens capable of changing its curvature due to the work of the ciliary muscle. It does not have blood vessels and nerves, and inflammatory processes do not develop here. Its refractive power is 20 diopters. It contains a lot of protein; in the pathological process, the lens loses its transparency. A cloudy lens is called a cataract. With age, the ability to accommodate may deteriorate (presbyopia).
Vitreous . This is the light-conducting medium of the eye, located between the lens and the fundus. It is a viscous gel that provides eye turgor (tone).
Watery moisture. Intraocular fluid fills the anterior and posterior chambers of the eye. It consists of 99% water and contains 1% protein fractions.
Blood supply to the eye and orbit carried out by the orbital artery from the pool of the internal carotid artery. Venous outflow is carried out by the superior and inferior orbital veins. The superior ocular vein carries blood into the cavernous sinus of the brain and through the angular vein anastomoses with the veins of the face. The veins of the orbit do not have valves. Consequently, the inflammatory process of the facial skin can spread into the cranial cavity. Sensitive innervation of the eye and tissues of the orbit is carried out by 1 branch of the 5th pair of cranial nerves.
The eye is the light-receiving part of the optic tract. The light-sensing nerve endings of the retina (rods and cones) are called photoreceptors. The cones provide visual acuity, while the rods provide light perception, i.e. twilight vision. Most of the cones are concentrated in the center of the retina, and most of the rods are on its periphery. Therefore, a distinction is made between central and peripheral vision. Central vision is provided by cones and is characterized by two visual functions: visual acuity and color perception - color perception. Peripheral vision is vision provided by rods (twilight vision) and characterized by the field of vision and light perception.
8-11-2012, 12:40
Description
The eyeball has a complex structure. It has three skins and contents.Outer sheath the eyeball is represented by the cornea and sclera.
Middle (vascular) membrane the eyeball consists of three sections - the iris, the ciliary body and the choroid. All three parts of the choroid are combined under one more name - the uveal tract (tractus uvealis).
Inner shell the eyeball is represented by the retina, which is a light-sensitive apparatus.
The contents of the eyeball include vitreous body (corpus vitreum), lens or lens (lens), as well as aqueous humor of the anterior i rear cameras eyes (humoraquacus) - refractive apparatus. The eyeball of a newborn appears to be an almost spherical formation, its mass is approximately 3 g, the average (anteroposterior) size is 16.2 mm. As the child develops, the eyeball increases, especially rapidly during the first year of life, and by the age of five it does not differ significantly from the size of an adult. By the age of 12-15 (according to some sources, by the age of 20-25), its growth is completed and the dimensions are 24 mm (sagittal), 23 mm (horizontal and vertical) with a mass of 7-8 g.
The outer shell of the eyeball, 5/6 of which is the opaque fibrous membrane, is called sclera.
In the front part of the sclera passes into a transparent tissue - cornea.
Cornea- transparent, non-vascular tissue, a kind of "window" in the outer capsule of the eye. The function of the cornea is to refract and conduct light rays and protect the contents of the eyeball from adverse external influences. The refractive power of the cornea is almost 2.5 times greater than that of the lens, and averages about 43.0 D. Its diameter is 11-11.5 mm, and the vertical dimension is slightly less than the horizontal. The thickness of the cornea ranges from 0.5-0.6 mm (center) to 1.0 mm.
The diameter of the cornea of \u200b\u200ba newborn is on average 9 mm, by the age of five the cornea reaches 11 mm.
Due to its bulge, the cornea has a high refractive power. In addition, the cornea has high sensitivity (due to the fibers of the optic nerve, which is a branch trigeminal nerve), but in a newborn it is low and reaches the level of adult sensitivity by about a year of the child's life.
Normal cornea - transparent, smooth, shiny, spherical and highly sensitive fabric. High sensitivity of the cornea to mechanical, physical and chemical attack along with its high strength, it provides an effective protective function. Irritation of sensitive nerve endings located under the epithelium of the cornea and between its cells leads to reflexive compression of the eyelids, protecting the eyeball from adverse external influences. This mechanism works in just 0.1 s.
The cornea consists of five layers:
- anterior epithelium,
- bowman membrane,
- stroma,
- descemet membrane
- and posterior epithelium (endothelium).
Nutrition of the cornea occurs due to the limbal vasculature and moisture in the anterior chamber of the eye. Normally, there are no blood vessels in the cornea.
The transparency of the cornea is ensured by its homogeneous structure, the absence of blood vessels and a strictly defined water content.
The osmotic pressure of the lacrimal fluid and moisture in the anterior chamber is greater than in the cornea tissue. Therefore, the excess water coming from the capillaries located around the cornea in the limbus region is removed in both directions - outward and into the anterior chamber.
Violation of the integrity of the anterior or posterior epithelium leads to "hydration" of the corneal tissue and the loss of its transparency.
The penetration of various substances into the eye through the cornea occurs as follows: fat-soluble substances pass through the anterior epithelium, and the stroma passes water-soluble compounds. Thus, to pass through all layers of the cornea, medicinal product must be both water and fat soluble.
The place where the cornea passes into the sclera is called limb- it is a semi-transparent bezel with a width of about 0.75-1.0 mm. It is formed as a result of the fact that the cornea is inserted into the sclera like a watch glass, where transparent corneal tissue, located deeper, shines through the opaque layers of the sclera. The Schlemm canal is located in the thickness of the limb, so many surgical interventions with glaucoma, they are produced in this place.
The limbus serves as a good guide when performing surgical interventions.
Sclera - tunica albuginea - consists of dense collagen fibers. The thickness of the sclera of an adult varies from 0.5 to 1 mm, and at the posterior pole, in the area of \u200b\u200bthe optic nerve exit, it is 1 - 1.5 mm.
The sclera of a newborn is much thinner and has a bluish color due to the transmission of the choroid pigment through it. The sclera has many elastic fibers, as a result of which it is capable of significant stretching. With age, this ability is lost, the sclera acquires white colorand yellowish in the elderly.
Scleral functions - protective and shaping. The thinnest part of the sclera is located at the exit site of the optic nerve, where its inner layers are a lattice plate, pierced by bundles of nerve fibers. The sclera is saturated with water and is opaque. With a sharp dehydration of the body, for example, with cholera, dark spots appear on the sclera. Its dehydrated tissue becomes transparent, and the pigmented choroid begins to shine through it. Numerous nerves and blood vessels pass through the sclera. Intraocular tumors can grow in the course of the vessels through the scleral tissue.
Middle shell of the eyeball (the choroid or uveal tract) consists of three parts: the iris, ciliary body, and choroid.
Vessels of the choroid, like all vessels of the eyeball, are branches of the ophthalmic artery.
The uveal tract lines the entire inner surface of the sclera. The choroid is not adjacent to the sclera: between them there is a looser tissue - suprachoroidal. The latter is rich in slits, which generally represent the suprachoroidal space.
Irisit got its name for the coloration that determines the color of the eyes. However, a permanent color of the iris is formed only by the age of two. Before that, it has a blue color due to the insufficient number of pigment cells (chromatophores) in the anterior leaflet. The iris is the automatic diaphragm of the eye. The ego is a rather thin formation with a thickness of only 0.2-0.4 mm, and the thinnest part of the iris is the place of its transition to the ciliary body. Here, detachment of the iris from its root can occur during trauma. The iris consists of a connective tissue stroma and an epithelial posterior layer, represented by two layers of pigmented cells. It is this leaf that provides the iris opacity and forms the pigment border of the pupil. In front, the iris, with the exception of the spaces between the connective tissue lacunae, is covered with epithelium, which passes into the posterior epithelium (endothelium) of the cornea. Therefore, in inflammatory diseases that involve the deep layers of the cornea, the iris is also involved in the process. The iris contains a relatively small number of sensitive endings. therefore inflammatory diseases the iris is accompanied by moderate pain syndrome.
The stroma of the iris contains a large number of cells - chromatophorescontaining pigment. Its amount determines the color of the eyes. In inflammatory diseases of the iris, the color of the eyes changes due to hyperemia of its vessels (the gray iris turns green, and the brown one gets a "rusty" hue). Violated due to exudation and clarity of the iris pattern.
Blood supply to the iris provide the vessels located around the cornea, therefore, pericorneal injection (vasodilation) is characteristic of iris diseases. With diseases of the iris, a pathological impurity may appear in the moisture of the anterior chamber - blood (hyphema), fibrin and pus (hycopion). If fibrin exudate occupies the area of \u200b\u200bthe pupil in the form of a film or numerous strands, adhesions are formed between the posterior surface of the iris and the anterior surface of the lens - posterior synechiae that deform the pupil.
In the center of the iris there is a round hole with a diameter of 3-3.5 mm - pupil, which reflexively (under the influence of light, emotions, when looking into the distance, etc.) changes the value, playing the role of a diaphragm.
If there is no pigment in the back leaf of the iris (in albinos), then the role of the iris is lost, which leads to a decrease in vision.
The size of the pupil changes under the action of two muscles - sphincter and dilator... The annular fibers of the smooth muscle of the sphincter located around the pupil are innervated parasympathetic fibersgoing with the third pair of cranial nerves. Radial smooth muscle fibers located in the peripheral iris are innervated by sympathetic fibers from the superior cervical sympathetic node. Due to the constriction and expansion of the pupil, the flow of light rays is maintained at a certain level, which will create the most favorable conditions for the act of vision.
The muscles of the iris in newborns and young children are poorly developed, especially the dilatator (dilating pupil), which makes it difficult to medically expand the pupil.
The second section of the uveal tract is located behind the iris - ciliary body (ciliary body) - part of the choroid of the eye, goes from the choroid to the root of the iris - a ring-shaped, protruding into the cavity of the eye, a kind of thickening of the vascular tract, which can be seen only when the eyeball is cut.
The ciliary body has two functions - production of intraocular fluid and participation in the act of accommodation. The ciliary body contains the muscle of the same name, consisting of fibers with different directions. The main (circular) part of the muscle receives parasympathetic innervation (from the oculomotor nerve), the radial fibers are innervated by the sympathetic nerve.
The ciliary body consists of process and flat parts. The processional part of the ciliary body occupies an area approximately 2 mm wide, and the flat part approximately 4 mm. Thus, the ciliary body ends at a distance of 6-6.5 mm from the limbus.
In the more convex process part, there are about 70 ciliary processes, from which thin fibers of the Cinna ligament stretch to the equator of the lens, keeping the lens suspended. Both the iris and the ciliary body have abundant sensory (from the first branch of the trigeminal nerve) innervation, but in childhood (up to 7-8 years) it is not sufficiently developed.
In the ciliary body, two layers are distinguished - vascular(internal) and muscular(outer). The vascular layer is most pronounced in the area of \u200b\u200bthe ciliary processes, which are covered with two layers of the epithelium, which is a reduced retina. Its outer layer is pigmented, but the inner one has no pigment, both of these layers continue in the form of two layers of pigmented epithelium covering the posterior surface of the iris. The anatomical features of the ciliary body determine some of the symptoms in its pathology. First, the ciliary body has the same source of blood supply as the iris (pericorneal vascular network that forms from the anterior ciliary arteries, which are a continuation of the muscular arteries, two posterior long arteries). Therefore, its inflammation (cyclitis), as a rule, proceeds simultaneously with inflammation of the iris (iridocyclitis), in which the pain syndrome is sharply expressed due to a large number of sensitive nerve endings.
Secondly, intraocular fluid is produced in the ciliary body. Depending on the amount of this fluid, intraocular pressure can change both in the direction of its decrease and increase.
Thirdly, with inflammation of the ciliary body, accommodation is always disturbed.
Ciliary body - the flat part of the ciliary body - passes into the choroid itself, or choroid) - the third and most extensive section of the uveal tract on the surface. The place of transition of the ciliary body to the choroid corresponds to the dentate line of the retina. Choroid - the posterior part of the uveal tract, located between the retina and the sclera and provides nutrition to the outer layers of the retina. It consists of several layers of vessels. Directly to the retina (its pigmented epithelium) is a layer of wide choriocapillaries, which is separated from it by a thin Bruch membrane. Then there is a layer of middle vessels, mainly arterioles, behind which there is a layer of larger vessels - venules. There is a space between the sclera and choroid, in which vessels and nerves mainly pass. In the choroid, as in other parts of the uveal tract, pigment cells are located. The choroid is tightly fused with other tissues around the optic nerve head.
Choroidal blood supply carried out from another source - the posterior short ciliary arteries. Therefore, inflammation of the choroid (choroiditis) often proceeds in isolation from anterior section uveal tract.
In inflammatory diseases of the choroid, the adjacent retina is always involved in the process and, depending on the localization of the focus, there are corresponding disorders of visual functions. Unlike the iris and the ciliary body, there are no sensitive endings in the choroid, so its diseases are painless.
The blood flow in the choroid is slow, which contributes to the emergence in this part of the choroid of the eye of metastases of tumors of various localization and the settling of pathogens of various infectious diseases.
The inner lining of the eyeball - the retina, the innermost, most complex in structure and the most physiologically important shell, which is the beginning, the peripheral part of the visual analyzer. It is followed, as in any analyzer, by pathways, subcortical and cortical centers.
The retina is highly differentiated nervous tissuedesigned to perceive light stimuli. The optically active part of the retina is located from the optic nerve head to the dentate line. Anterior to the dentate line, it is reduced to two layers of the epithelium, covering the ciliary body and the iris. This part of the retina is not involved in the act of sight. The optically active retina along its entire length is functionally connected with the adjacent choroid, but is fused with it only at the dentate line in front and around the optic nerve head and along the edge of the macula behind.
The optically inactive part of the retina lies anterior to the dentate line and is not essentially a retina membrane - it loses its complex structure and consists only of two layers of the epithelium lining the ciliary body, the posterior surface of the iris and forming the pigment fringe of the pupil.
Normally, the retina is a thin transparent shell about 0.4 mm thick. Its thinnest part is located in the area of \u200b\u200bthe dentate line and in the center - in the macula, where the thickness of the retina is only 0.07-0.08 mm. The macula has the same diameter as the optic disc, 1.5 mm, and is located 3.5 mm to the temple and 0.5 mm below the optic disc.
Histologically, 10 layers are distinguished in the retina. It contains and three neurons of the visual pathway: rods and cones (first), bipolar cells (second) and ganglion cells (third neuron). The rods and cones are the receptor portion of the visual pathway. The cones, the bulk of which are concentrated in the macular region and, first of all, in its central part, provide visual acuity and color perception, while the rods located more peripherally provide the field of vision and light perception.
Rods and cones are located in the outer layers of the retina, directly at its pigment epithelium, to which the choriocapillary layer is adjacent.
For visual functions not to suffer, transparency of all other layers of the retina located in front of the photoreceptor cells is necessary.
In the retina, three neurons are distinguished, located one after the other.
- First neuron - retinal neuroepithelium with corresponding nuclei.
- Second neuron - a layer of bipolar cells, each of its cells is in contact with the endings of several cells of the first neuron.
- Third neuron - a layer of ganglion cells, each of its cells is associated with several cells of the second neuron.
The inner surface of the eyeball, lined with the optically active part of the retina, is called the fundus. There are two important formations on the fundus: the macula, located in the region of the posterior pole of the eyeball (the name is associated with the presence of yellow pigment when examining this area in redless light), and the optic nerve head - the beginning of the visual path.
Optic nerve head appears to be a well-defined pale pink oval, 1.5-1.8 mm in diameter, located about 4 mm from the macula. In the area of \u200b\u200bthe optic nerve head, the retina is absent, as a result of which the area of \u200b\u200bthe fundus corresponding to this place is also called the physiological blind spot, discovered by Mariotte (1663). It should be noted that in newborns the optic nerve head is pale, with a bluish-gray tint, which can be mistaken for atrophy.
It leaves the optic nerve head and branches on the fundus central retinal artery... In the thickness of the optic nerve, the specified artery, separated in the orbit from the ophthalmic, penetrates 10-12 mm from the posterior pole of the eye. The artery is accompanied by a vein of the corresponding name. The arterial branches look lighter and thinner than the venous ones. The ratio of the diameter of the arteries to the diameter of the veins n normal in adults is 2: 3. In children under 10 years of age -1: 2. Arteries and veins spread with their branches over the entire surface of the retina, its light-sensitive layer is fed by the choriocapillary choroid.
Thus, the retina is nourished from the choroid and its own arterial vascular system - central retinal arteriole and its branches... This arteriole is a branch of the orbital artery, which in turn arises from the internal carotid artery in the cranial cavity. Thus, examination of the fundus allows us to judge the state of the cerebral vessels, which have the same source of blood circulation - the internal carotid artery... The macular region is supplied with blood by the choroid; the retinal vessels do not pass here and do not prevent light rays from reaching the photoreceptors.
In the central fossa, only cones are located, all other layers of the retina are pushed back to the periphery. Thus, in the area of \u200b\u200bthe macula, light rays fall directly on the cones, which ensures the high resolution of this zone. This is also ensured by a special ratio between the cells of all retinal neurons: in the central fossa there is one bipolar cell for one cone, and for each bipolar cell there is its own ganglionic cell. This provides a "direct" connection between the photoreceptors and the visual centers.
On the periphery of the retina, on the contrary, there is one bipolar cell for several rods, and one ganglionic cell for several bipolar ones, which “sums up” irritation from a certain part of the retina. This summation of irritations provides the peripheral part of the retina with extremely high sensitivity to the minimum amount of light entering the human eye.
Beginning in the fundus in the form of a disk, the optic nerve leaves the eyeball, then the orbit and in the area of \u200b\u200bthe sella turcica meets the nerve of the second eye. Located in the orbit, the optic nerve is S-shaped, which excludes the possibility of tension on its fibers during the movements of the eyeball. In the bony canal of the orbit, the nerve loses the dura mater and remains covered with cobwebs and pia mater.
In the Turkish saddle, an incomplete intersection (internal halves) of the optic nerves is carried out, called chiasma... After partial intersection, the visual pathways change their name and are referred to as visual tracts. Each of them carries fibers from the outer parts of the retina of the eye on its side and from the inner parts of the retina of the second eye. The optic tracts are directed to the subcortical visual centers - the external geniculate bodies. From the multipolar cells of the geniculate bodies, the fourth neurons begin, which in the form of diverging bundles (right and left) of Graspole pass through the internal capsule and end in the spur grooves of the occipital lobes of the brain.
Thus, in each half of the brain the retinas of both eyes are represented, determining the corresponding half of the visual field, which made it possible to figuratively compare the control system from the side of the brain with visual functions with the control of a rider by a pair of horses, when the reins from the right half of the bridle are in the right hand of the rider, and in the left - from the left.
Fibers (axons) of ganglion cells converge, forming optic nerve... The optic nerve head consists of bundles of nerve fibers, therefore, this area of \u200b\u200bthe fundus is not involved in the perception of a ray of light and, when examining the visual field, gives the so-called blind spot. The axons of the ganglion cells inside the eyeball do not have a myelin sheath, which ensures the transparency of the tissue.
Retinal pathology, with rare exceptions, leads to some kind of visual impairment. Already because of which of them is violated, one can assume where the lesion is located. For example, a patient has decreased visual acuity, impaired color perception with preserved peripheral vision and light perception. Naturally, in this case, there is reason to think about the pathology of the macular region of the retina. At the same time, with a sharp narrowing of the field of vision and color perception, it is logical to assume the presence of changes in the peripheral parts of the retina.
There are no sensitive nerve endings in the retina, therefore, all diseases are painless. The vessels feeding the retina pass into the eyeball from behind, near the exit site of the optic nerve, and when it is inflamed, there is no visible hyperemia of the eye.
Diagnosis of retinal diseases is carried out on the basis of anamnesis data, the determination of visual functions, primarily visual acuity, visual field and dark adaptation, as well as an ophthalmoscopic picture.
The optic nerve (the eleventh pair of cranial nerves) is composed of approximately 1,200,000 axons of retinal ganglion cells. The optic nerve accounts for about 38% of all afferent and efferent nerve fibers found on all cranial nerves.
There are four parts of the optic nerve:
- intrabulbar (intraocular),
- orbital,
- intracanal (intraosseous)
- and intracranial.
Intraocular part very short (0.7 mm long). The optic nerve head is only 1.5 mm in diameter and determines the physiological scotoma - a blind spot. In the area of \u200b\u200bthe optic nerve head runs the central artery and the central retinal vein.
Orbital part the optic nerve is 25-30 mm long. Immediately behind the eyeball, the optic nerve becomes much thicker (4.5 mm), since its fibers receive the myelin sheath, supporting tissue - neuroglia, and the entire optic nerve - the meninges, hard, soft and arachnoid, between which cerebrospinal fluid circulates. These membranes blindly end at the eyeball, and with an increase in intracranial pressure, the optic nerve head becomes edematous and rises above the level of the retina, mushroom-like protruding into the vitreous body. A stagnant disc of the optic nerve arises, characteristic of brain tumors and other brain diseases, accompanied by an increase in intracranial pressure.
With an increase in intraocular pressure, a thin lattice plate of the sclera is displaced posteriorly and a pathological depression is formed in the region of the optic nerve head - the so-called glaucomatous expansion.
The orbital part of the optic nerve is 25-30 mm long. In the orbit, the optic nerve lies freely and makes an S-shaped bend, which eliminates its tension even with significant displacements of the eyeball. In the orbit, the optic nerve is close enough to paranasal sinuses nose, therefore, with their inflammation, rhinogenic neuritis may occur.
Inside the bony canal, the optic nerve passes along with the orbital artery. With the thickening and compaction of its wall, compression of the optic nerve can occur, leading to a gradual atrophy of its fibers. With fractures of the base of the skull, the optic nerve can be compressed or cut by bone debris.
Myelin sheath of the optic nerve is often involved in the pathological process in demyelinating diseases of the central nervous system (multiple sclerosis), which can also lead to optic nerve atrophy.
Inside the skull, the fibers of the optic nerves of both eyes make a partial intersection, forming a chiasm. Fibers from the nasal halves of the retinas intersect and pass to the opposite side, while the fibers from the temporal halves of the retinas continue their course without crossing.
The choroid or choroid is the middle layer of the eye that lies between the sclera and the retina. Most of the choroid is represented by a well-developed network of blood vessels. The blood vessels are located in the choroid in a certain order - there are larger vessels outside, and inside, on the border with the retina, there is a layer of capillaries.The main function of the choroid is to provide nutrition to the four outer layers of the retina, which includes the rod and cone layer, and to remove metabolic products from the retina back into the bloodstream. The capillary layer is delimited from the retina by a thin Bruch membrane, whose function is to regulate metabolic processes between the retina and the choroid. In addition, the peri-vascular space, due to its loose structure, serves as a conductor for the posterior long ciliary arteries involved in the blood supply to the anterior segment of the eye.
Choroid structure
The choroid itself is the most extensive part of the vascular tract of the eyeball, which also includes the ciliary body and the iris. It extends from the ciliary body, the border of which is the dentate line, to the optic nerve head.Choroid is provided with blood flow through the posterior short ciliary arteries. The outflow of blood occurs through the so-called vorticose veins. A small number of veins - only one for each quarter, or quadrant, of the eyeball and pronounced blood flow help slow blood flow and a high probability of developing inflammatory infectious processes due to the settling of pathogenic microbes. The choroid is devoid of sensitive nerve endings, for this reason all its diseases are painless.
Choroid is rich in dark pigment, which is located in special cells called chromatophores. The pigment is very important for vision, as light rays entering through open areas of the iris or sclera would interfere with good eyesight due to spilled retinal illumination or lateral flares. The amount of pigment contained in this layer also determines the color intensity of the fundus.
According to its name, for the most part, the choroid consists of blood vessels. The choroid includes several layers: the perivascular space, supravascular, vascular, vascular-capillary and basal layers.
The perivascular or perichoroidal space is a narrow gap between the inner surface of the sclera and the vascular plate, which is penetrated by delicate endothelial plates. These plates connect the walls together. However, due to the weak connections between the sclera and choroid in this space, the choroid peels off the sclera quite easily, for example, in case of intraocular pressure drops during operations for glaucoma. In the perichoroidal space from the posterior to the anterior segment of the eye, two blood vessels - long posterior ciliary arteries, accompanied by nerve trunks.
The supravascular plate consists of endothelial laminae, elastic fibers and chromatophores - cells containing dark pigment. The number of chromatophores in the layers of the choroid decreases rapidly from the outside to the inside, and they are completely absent in the choriocapillary layer. The presence of chromatophores can lead to the appearance of choroidal nevi and even the most aggressive malignant tumors - melanoma.
The vascular plate has the form of a brown membrane, up to 0.4 mm thick, and the layer thickness depends on the degree of blood filling. The vascular plate consists of two layers: large vessels lying outside with a large number of arteries and vessels of medium caliber, in which veins predominate.
The vascular capillary plate, or choriocapillary layer, is the most important layer of the choroid, ensuring the functioning of the underlying retina. It is formed from small arteries and veins, which then break down into many capillaries, allowing several red blood cells to pass in one row, which allows more oxygen to enter the retina. The network of capillaries is especially pronounced for the functioning of the macular region. The close connection of the choroid with the retina leads to the fact that inflammatory diseases, as a rule, affect both the retina and the choroid together.
Bruch's membrane is a thin plate made up of two layers. It is very tightly connected to the choriocapillary layer of the choroid and is involved in regulating the flow of oxygen to the retina and metabolic products back into the bloodstream. Bruch's membrane is also associated with the outer layer of the retina, the pigment epithelium. With age and in the presence of a predisposition, a violation of the function of a complex of structures may occur: the choriocapillary layer, Brucha's membrane and pigment epithelium, with the development of age-related macular degeneration.
Methods for diagnosing diseases of the choroid
- Ophthalmoscopy.
- Ultrasound diagnostics.
- Fluorescence angiography - assessment of the state of blood vessels, damage to Bruch's membrane, the appearance of newly formed vessels.
Symptoms for diseases of the choroid
Congenital changes:- Coloboma of the choroid is the complete absence of the choroid in a certain area.
- Dystrophy of the choroid.
- Inflammation of the choroid - choroiditis, but more often combined with damage to the retina - chorioretinitis.
- Detachment of the choroid, with changes in intraocular pressure during abdominal operations on the eyeball.
- Ruptures of the choroid, hemorrhages - most often due to eye injuries.
- Choroidal nevus.
- Tumors of the choroid.