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Organs of vision of fish. The structure of the human eye photo with a description. Anatomy and structure The structure of the muscles of the eye

The pigment layer from the inside is adjacent to the structure of the eye, referred to as Bruch's membrane. The thickness of this membrane is from 2 to 4 microns, it is also called a vitreous plate due to its complete transparency. The functions of the Bruch's membrane are to create antagonism of the ciliary muscle at the time of accommodation. Bruch's membrane also delivers nutrients and fluids to the pigment layer of the retina and to the choroid.

As the body ages, the membrane thickens and its protein composition changes. These changes lead to a slowdown in metabolic reactions, and the pigment epithelium in the form of a layer also develops in the boundary membrane. The ongoing changes indicate age-related diseases of the retina.

The size of the retina of an adult eye reaches 22 mm and covers approximately 72% of the entire area of the internal surfaces of the eyeball. The pigment epithelium of the retina, that is, its outermost layer, is associated with the choroid of the human eye more closely than with other structures of the retina.

In the center of the retina, in the part that is closer to the nose, on the back side of the surface there is an optic disc. There are no photoreceptors in the disc, and therefore it is designated in ophthalmology by the term "blind spot". In the photo taken during microscopic examination of the eye, the "blind spot" looks like an oval shape of a pale shade, slightly rising above the surface and having a diameter of about 3 mm. It is in this place that the primary structure of the optic nerve begins from the axons of ganglionic neurocytes. The central part of the human retinal disc has a depression through which the vessels pass. Their function is to supply blood to the retina.

On the side of the optic disc, at a distance of about 3 mm, there is a spot. In the central part of this spot is located the central fossa - a recess, which is the most sensitive area of the human retina to the light flux.

The fovea fovea is the so-called "yellow spot", which is responsible for clear and sharp central vision. In the "yellow spot" of the human retina, there are only cones.

Humans (as well as other primates) have their own peculiarities in the structure of the retina. Humans have a central fovea, while some species of birds, as well as cats and dogs, have a "optic streak" instead of this fovea.

The retina in its central part is represented only by the fovea and the area surrounding it, which is located within a radius of 6 mm. Then comes the peripheral part, where the number of cones and rods gradually decreases towards the edges. All the inner layers of the retina end with a jagged edge, the structure of which does not imply the presence of photoreceptors.

The thickness of the retina throughout its length is not the same. In the thickest part near the edge of the optic disc, the thickness reaches 0.5 mm. The smallest thickness was found in the region of the corpus luteum, or rather its fossa.

Microscopic structure of the retina

The anatomy of the retina at the microscopic level is represented by several layers of neurons. There are two layers of synapses and three layers of nerve cells located radically.
In the deepest part of the human retina, there are ganglion neurons, rods and cones, while they are farthest from the center. In other words, this structure makes the retina an inverted organ. That is why light, before reaching the photoreceptors, must penetrate all the inner layers of the retina. However, the light flux does not penetrate the pigment epithelium and choroid, as they are opaque.

There are capillaries in front of the photoreceptors, which is why leukocytes, when looking at a source of blue light, are often perceived as tiny moving dots that have a light color. Such features of vision in ophthalmology are referred to as the Shearer phenomenon or the entopic phenomenon of the blue field.

In addition to ganglion neurons and photoreceptors, there are also bipolar nerve cells in the retina, their functions are to transfer contacts between the first two layers. Horizontal connections in the retina are carried out by amacrine and horizontal cells.

On a highly enlarged photo of the retina, between the layer of photoreceptors and the layer of ganglion cells, you can see two layers consisting of plexuses of nerve fibers and having many synaptic contacts. These two layers have their own names - the outer plexiform layer and the inner plexiform layer. The functions of the first are to make continuous contacts between cones and rods and also between vertical bipolar cells. The inner plexiform layer switches the signal from bipolar cells to ganglion neurons and to amacrine cells located in the horizontal and vertical direction.

From this we can conclude that the nuclear layer, located outside, contains photosensory cells. The inner nuclear layer includes the bodies of bipolar amacrine and horizontal cells. The ganglionic layer directly includes the ganglionic cells themselves and also a small number of amacrine cells. All layers of the retina are permeated with Muller cells.

The structure of the outer limiting membrane is represented by synaptic complexes, which are located between the outer layer of ganglion cells and between photoreceptors. The layer of nerve fibers is formed by the axons of ganglion cells. The basement membranes of Müller cells and the endings of their processes take part in the formation of the inner limiting membrane. Axons of ganglion cells that do not have Schwann membranes, having reached the inner border of the retina, turn at a right angle and go to the place where the optic nerve is formed.
The retina of any person contains from 110 to 125 million rods and from 6 to 7 million cones. These photosensitive elements are located unevenly. In the central part there is the maximum number of cones, in the peripheral part there are more rods.

Retinal diseases

Many acquired and hereditary eye diseases have been identified, in which the retina can also be involved in the pathological process. This list includes the following:

pigmentary degeneration of the retina (it is hereditary, with its development the retina is affected and peripheral vision is lost);
macular degeneration (a group of diseases, the main symptom of which is the loss of central vision);
macular degeneration of the retina (also hereditary, associated with a symmetrical bilateral lesion of the macular zone, loss of central vision);
rod-cone dystrophy (occurs when the photoreceptors of the retina are damaged);
retinal detachment (separation from the back of the eyeball, which can occur under the influence of inflammation, degenerative changes, as a result of injuries);
retinopathy (caused by diabetes mellitus and arterial hypertension);
retinoblastoma (malignant tumor);
macular degeneration (pathology of blood vessels and malnutrition of the central region of the retina).

Organ of vision Eye- This is the perceiving department of the visual analyzer, which serves to perceive light stimuli. Consists of an eyeball and an auxiliary apparatus.

The human eye perceives light waves of a certain length - from 390 to 760 nm. The sensitivity of the retina is very high, the light of an ordinary candle is visible at a distance of several kilometers.

Adaptation- adaptability of the eye to the perception of light of different brightness.

Accommodation The ability of the eye to clearly see objects at different distances. Due to the elasticity of the lens, its curvature, and hence the power of refraction of the rays, can change.

Diagram of the structure of the eye

The structure and function of the parts of the eye

Eye systems	Parts of the eye	The structure of the parts of the eye	Functions
Auxiliary	Brows	Hair growing from inner to outer corner of the eye	Remove sweat from forehead
	Eyelids	Skin folds with eyelashes	Eye protection from wind, dust, bright rays
	lacrimal apparatus	Lacrimal glands and lacrimal ducts	Tears wet, cleanse, disinfect the eye
Shells	Belochnaya	The outer dense shell, consisting of connective tissue "	Eye protection from mechanical and chemical damage, from microorganisms
	Vascular	The middle layer is permeated with blood vessels. The inner surface contains a layer of black pigment	Nourishing the eye, the pigment absorbs light rays
	Retina	Inner shell of the eye, consisting of photoreceptors: rods and cones	Perception of light, converting it into nerve impulses
Optical	Cornea	Transparent anterior part of the albuginea	Refracts rays of light
	aqueous humor	clear fluid behind the cornea	Transmits rays of light
	Iris (iris)	Anterior part of choroid with pigment and muscles	The pigment gives color to the eye, the muscles change the size of the pupil
	Pupil	Hole in the iris	Regulates the amount of light by expanding and contracting
	lens	Biconvex elastic clear lens surrounded by ciliary muscle	Refracts and focuses rays of light, has accommodation
	vitreous body	transparent gelatinous substance	Fills the eyeball. Supports intraocular pressure. Transmits rays of light
Light-receiving	Photoreceptors (neurons)	Arranged in the retina in the form of rods and cones	Rods perceive shape (low light vision), cones perceive color (color vision)

visual analyzer

The visual analyzer provides the perception of the size, shape and color of objects, their relative position and the distance between them.

Diagram of the structure of the visual analyzer

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The source of information:

Biology in tables and diagrams. / Edition 2e, - St. Petersburg: 2004.

Rezanova E.A. Human biology. In tables and diagrams./ M.: 2008.

The eye apparatus is stereoscopic and in the body is responsible for the correct perception of information, the accuracy of its processing and further transmission to the brain.

The right part of the retina sends information from the right lobe of the image to the brain by means of transmission through the optic nerve, the left part transmits the left lobe, as a result, the brain connects both, and a common visual picture is obtained.

The lens is fixed with thin threads, one end of which is tightly woven into the lens, its capsule, and the other end is connected to the ciliary body.

When the tension of the threads changes, the process of accommodation occurs . The lens is devoid of lymphatic vessels and blood vessels, as well as nerves.

It provides the eye with light transmission and light refraction, endows it with the function of accommodation, and is the eye's divider into the posterior and anterior regions.

vitreous body

The vitreous body of the eye is the largest formation. This is a colorless substance of a gel-like substance, which is formed in the form of a spherical shape, in the sagittal direction it is flattened.

The vitreous body consists of a gel-like substance of organic origin, a membrane and a vitreous canal.

In front of it is the lens, zonular ligament and ciliary processes, its back part comes close to the retina. The connection of the vitreous body and the retina occurs at the optic nerve and in the part of the dentate line, where the flat part of the ciliary body is located. This area is the base of the vitreous body, and the width of this belt is 2-2.5 mm.

The chemical composition of the vitreous body: 98.8 hydrophilic gel, 1.12% dry residue. When a hemorrhage occurs, the thromboplastic activity of the vitreous body increases dramatically.

This feature is aimed at stopping bleeding. In the normal state of the vitreous body, fibrinolytic activity is absent.

Nutrition and maintenance of the vitreous body environment is provided by the diffusion of nutrients that through the vitreous membrane enter the body from the intraocular fluid and osmosis.

There are no vessels and nerves in the vitreous body, and its biomicroscopic structure presents various forms of gray ribbons with white speckles. Between the ribbons there are areas without color, completely transparent.

Vacuoles and opacities in the vitreous body appear with age. In the case when there is a partial loss of the vitreous body, the place is filled with intraocular fluid.

Chambers with aqueous humor

The eye has two chambers that are filled with aqueous humor. Moisture is formed from the blood by processes of the ciliary body. Its release occurs first in the anterior chamber, then it enters the anterior chamber.

Aqueous moisture enters the anterior chamber through the pupil. The human eye produces 3 to 9 ml of moisture per day. Aqueous moisture contains substances that nourish the lens, the corneal endothelium, the anterior vitreous, and the trabecular meshwork.

It contains immunoglobulins that help remove dangerous factors from the eye, its inner part. If the outflow of aqueous humor is impaired, then this can develop an eye disease such as glaucoma, as well as an increase in pressure inside the eye.

In cases of violation of the integrity of the eyeball, the loss of aqueous humor leads to hypotension of the eye.

Iris

The iris is the avant-garde part of the vascular tract. It is located just behind the cornea, between the chambers and in front of the lens. The iris is round in shape and is located around the pupil.

It consists of a boundary layer, a stromal layer, and a pigment-muscle layer. It has an uneven surface with a pattern. The iris contains pigment cells, which are responsible for the color of the eyes.

The main tasks of the iris: regulation of the light flux that passes to the retina through the pupil and protection of light-sensitive cells. Visual acuity depends on the correct functioning of the iris.

The iris has two muscle groups. One group of muscles is deployed around the pupil and regulates its reduction, the other group is deployed radially along the thickness of the iris, regulating the expansion of the pupil. The iris has many blood vessels.

Retina

It is an optimally thin shell of the nervous tissue and represents the peripheral part of the visual analyzer. In the retina there are photoreceptor cells that are responsible for perception, as well as for converting electromagnetic radiation into nerve impulses. It is adjacent from the inside to the vitreous body, and to the vascular layer of the eyeball - from the outside.

The retina has two parts. One part is visual, the other is the blind part, which does not contain photosensitive cells. The internal structure of the retina is divided into 10 layers.

The main task of the retina is to receive the light flux, process it, converting it into a signal that forms complete and encoded information about the visual image.

optic nerve

The optic nerve is a network of nerve fibers. Among these thin fibers is the central canal of the retina. The starting point of the optic nerve is located in the ganglion cells, then its formation occurs by passing through the sclera membrane and fouling of the nerve fibers with meningeal structures.

The optic nerve has three layers - hard, arachnoid, soft. There is liquid between the layers. The diameter of the optic disc is about 2 mm.

Topographic structure of the optic nerve:

intraocular;
intraorbital;
intracranial;
intratubular;

How the human eye works

The light flux passes through the pupil and through the lens is brought into focus on the retina. The retina is rich in light-sensitive rods and cones, of which there are more than 100 million in the human eye.

Video: "The process of vision"

The rods provide sensitivity to light, and the cones give the eyes the ability to see colors and small details. After the refraction of the light flux, the retina transforms the image into nerve impulses. Further, these impulses pass to the brain, which processes the information received.

Diseases

Diseases associated with a violation of the structure of the eye can be caused both by an incorrect arrangement of its parts in relation to each other, and by internal defects in these parts.

The first group includes diseases that lead to a decrease in visual acuity:

Myopia. It is characterized by an increased length of the eyeball compared to the norm. This causes the light passing through the lens to be focused not on the retina, but in front of it. The ability to see objects at a distance from the eyes is impaired. Myopia corresponds to a negative number of diopters when measuring visual acuity.
Farsightedness. It is a consequence of a decrease in the length of the eyeball or loss of elasticity of the lens. In both cases, the accommodative possibilities are reduced, the correct focusing of the image is disturbed, and the light rays converge behind the retina. The ability to see nearby objects is impaired. Farsightedness corresponds to a positive number of diopters.
Astigmatism. This disease is characterized by a violation of the sphericity of the eye membrane due to defects in the lens or cornea. This leads to an uneven convergence of the rays of light entering the eye, the clarity of the image received by the brain is disturbed. Astigmatism is often accompanied by nearsightedness or farsightedness.

Pathologies associated with functional disorders of certain parts of the organ of vision:

Cataract. With this disease, the lens of the eye becomes cloudy, its transparency and ability to conduct light are disturbed. Depending on the degree of clouding, visual impairment can be different up to complete blindness. Most people develop cataracts in old age but do not progress to severe stages.
Glaucoma is a pathological change in intraocular pressure. It can be provoked by many factors, for example, a decrease in the anterior chamber of the eye or the development of cataracts.
Myodesopsia or "flying flies" before the eyes. It is characterized by the appearance of black dots in the field of view, which can be presented in different quantities and sizes. Points arise due to violations in the structure of the vitreous body. But in this disease, the causes are not always physiological - “flies” can appear due to overwork or after suffering infectious diseases.
Strabismus. It is provoked by a change in the correct position of the eyeball in relation to the eye muscle or a violation of the work of the eye muscles.
Retinal detachment. The retina and posterior vascular wall are separated from each other. This is due to a violation of the tightness of the retina, which occurs when its tissues break. Detachment is manifested by clouding of the outline of objects before the eyes, the appearance of flashes in the form of sparks. If some corners fall out of the field of view, this means that the detachment has taken severe forms. If left untreated, complete blindness occurs.
Anophthalmos - underdevelopment of the eyeball. A rare congenital pathology, the cause of which is a violation of the formation of the frontal lobes of the brain. Anophthalmos can also be acquired, then it develops after surgical operations (for example, to remove tumors) or severe eye injuries.

Prevention

You should take care of the health of the circulatory system, especially that part of it that is responsible for the flow of blood to the head. Many visual defects are due to atrophy and damage to the ophthalmic and brain nerves.
Eye strain must not be allowed. When working with constant examination of small objects, you need to take regular breaks with eye exercises. The workplace should be equipped so that the brightness of the lighting and the distance between objects are optimal.
The intake of a sufficient amount of minerals and vitamins in the body is another condition for maintaining healthy vision. Vitamins C, E, A and minerals such as zinc are especially important for the eyes.
Proper eye hygiene helps prevent the development of inflammatory processes, the complications of which can significantly impair vision.

Bibliography

Ophthalmology. National leadership. Short edition Ed. S.E. Avetisova, E.A. Egorova, L.K. Moshetova, V.V. Neroeva, H.P. Tahchidi 2019
Atlas of ophthalmology G.K. Kriglstein, K.P. Ionescu-Cypers, M. Severin, M.A. Wobig 2009

The structure of the human eye includes many complex systems that make up the visual system, which provides information about what surrounds a person. The sense organs included in it, characterized as paired, are distinguished by the complexity of the structure and uniqueness. Each of us has individual eyes. Their features are exceptional. At the same time, the structure of the human eye and its functionality have common features.

Evolutionary development has led to the fact that the organs of vision have become the most complex formations at the level of structures of tissue origin. The main purpose of the eye is to provide vision. This possibility is guaranteed by blood vessels, connective tissues, nerves and pigment cells. Below is a description of the anatomy and main functions of the eye with symbols.

Under the scheme of the structure of the human eye, one should understand the entire eye apparatus having an optical system responsible for processing information in the form of visual images. This implies its perception, subsequent processing and transmission. All this is realized due to the elements that form the eyeball.

The eyes are rounded. Its location is a special recess in the skull. It is referred to as the eye. The outer part is closed with eyelids and folds of skin that serve to accommodate muscles and eyelashes.

Their functionality is as follows:

moisturizing, which is provided by the glands in the eyelashes. The secretory cells of this species contribute to the formation of the corresponding fluid and mucus;
protection against mechanical damage. This is achieved by closing the eyelids;
removal of the smallest particles falling on the sclera.

The functioning of the vision system is configured in such a way as to transmit the received light waves with maximum accuracy. In this case, a careful attitude is required. The sense organs in question are fragile.

Eyelids

Skin folds are what the eyelids are, which are constantly in motion. Flashing occurs. This possibility is available due to the presence of ligaments located along the edges of the eyelids. Also, these formations act as connecting elements. With their help, the eyelids are attached to the eye socket. The skin forms the top layer of the eyelids. Then comes the muscle layer. Next comes cartilage and conjunctiva.

The eyelids in the part of the outer edge have two ribs, where one is anterior and the other is posterior. They form an intermarginal space. The ducts from the meibomian glands exit here. With their help, a secret is developed that makes it possible to slide the eyelids with the utmost ease. At the same time, the density of closing of the eyelids is achieved, and conditions are created for the correct removal of the lacrimal fluid.

On the front rib there are bulbs that provide the growth of cilia. The ducts that serve as transport routes for the oily secret also come out here. Here are the conclusions of the sweat glands. The angles of the eyelids correspond with the findings of the lacrimal ducts. The back rib ensures that each eyelid fits snugly against the eyeball.

The eyelids are characterized by complex systems that provide these organs with blood and maintain the correct conduction of nerve impulses. The carotid artery is responsible for blood supply. Regulation at the level of the nervous system - the involvement of motor fibers that form the facial nerve, as well as providing appropriate sensitivity.

The main functions of the eyelid include protection against damage as a result of mechanical impact and foreign bodies. To this should be added the moisturizing function, which contributes to the saturation of the internal tissues of the organs of vision with moisture.

The eye socket and its contents

The bony cavity refers to the orbit, which is also referred to as the bony orbit. It serves as reliable protection. The structure of this formation includes four parts - upper, lower, outer and inner. They form a single whole due to a stable connection with each other. However, their strength is different.

The outer wall is especially reliable. The internal one is much weaker. Blunt traumas can provoke its destruction.

The features of the walls of the bone cavity include their proximity to the air sinuses:

inside - a lattice labyrinth;
bottom - maxillary sinus;
top - frontal emptiness.

Such structuring creates a certain danger. Tumor processes that develop in the sinuses can spread to the cavity of the orbit. The reverse action is also allowed. The eye socket communicates with the cranial cavity through a large number of holes, which suggests the possibility of inflammation moving to areas of the brain.

Pupil

The pupil of the eye is a round hole located in the center of the iris. Its diameter can be changed, which allows you to adjust the degree of penetration of the light flux into the inner region of the eye. The muscles of the pupil in the form of a sphincter and a dilator provide the conditions when the illumination of the retina changes. Activation of the sphincter constricts the pupil, and the dilator dilates it.

Such functioning of the mentioned muscles is akin to how the diaphragm of a camera works. Blinding light leads to a decrease in its diameter, which cuts off too intense light rays. Conditions are created when image quality is achieved. Lack of illumination leads to a different result. The diaphragm expands. The quality of the picture again remains high. Here we can talk about the diaphragm function. With its help, the pupillary reflex is provided.

The size of the pupils is adjusted automatically, if such an expression is acceptable. Human consciousness does not explicitly control this process. The manifestation of the pupillary reflex is associated with a change in the illumination of the retina. Absorption of photons starts the process of transmission of the relevant information, where addressees are understood as nerve centers. The required sphincter response is achieved after signal processing by the nervous system. Its parasympathetic department comes into action. As for the dilator, the sympathetic department comes into play here.

Pupil reflexes

The reaction in the form of a reflex is provided by sensitivity and excitation of motor activity. First, a signal is formed as a response to a certain impact, and the nervous system comes into play. This is followed by a specific reaction to the stimulus. Muscle tissues are included in the work.

Lighting causes the pupil to constrict. This cuts off blinding light, which has a positive effect on the quality of vision.

Such a reaction can be characterized as follows:

straight - one eye is illuminated. He reacts as required;
friendly - the second organ of vision is not illuminated, but responds to the light effect exerted on the first eye. The effect of this type is achieved by the fact that the fibers of the nervous system are partially crossed. Chiasma is formed.

The stimulus in the form of light is not the only reason for the change in the diameter of the pupils. Still possible are such moments as convergence - stimulation of the activity of the rectus muscles of the visual organ, and - the involvement of the ciliary muscle.

The appearance of the considered pupillary reflexes occurs when the point of stabilization of vision changes: the gaze is transferred from an object located at a great distance to an object located at a closer distance. The proprioreceptors of the mentioned muscles are activated, which is provided by the fibers going to the eyeball.

Emotional stress, such as pain or fear, stimulates pupil dilation. If the trigeminal nerve is irritated, and this indicates low excitability, then a narrowing effect is observed. Also, similar reactions occur when taking certain drugs that excite the receptors of the corresponding muscles.

optic nerve

The functionality of the optic nerve is to deliver the appropriate messages to certain areas of the brain designed to process light information.

Light pulses first hit the retina. The location of the visual center is determined by the occipital lobe of the brain. The structure of the optic nerve suggests the presence of several components.

At the stage of intrauterine development, the structures of the brain, the inner shell of the eye and the optic nerve are identical. This gives grounds to assert that the latter is a part of the brain that is outside the cranium. At the same time, ordinary cranial nerves have a different structure from it.

The optic nerve is short. It is 4–6 cm. It is mainly located behind the eyeball, where it is immersed in the fat cell of the orbit, which guarantees protection from damage from the outside. The eyeball in the part of the posterior pole is the site where the nerve of this species begins. In this place, there is an accumulation of nerve processes. They form a kind of disk (OND). This name is due to the flattened shape. Moving on, the nerve enters the orbit with subsequent immersion in the meninges. It then reaches the anterior cranial fossa.

The optic pathways form a chiasm within the skull. They intersect. This feature is important in diagnosing eye and neurological diseases.

Directly below the chiasm is the pituitary gland. How effectively the endocrine system is able to work depends on its condition. Such anatomy is clearly visible if the tumor processes affect the pituitary gland. Opto-chiasmal syndrome becomes the board of pathology of this type.

The internal branches of the carotid artery are responsible for supplying blood to the optic nerve. The insufficient length of the ciliary arteries excludes the possibility of a good blood supply to the optic disc. At the same time, other parts receive blood in full.

The processing of light information directly depends on the optic nerve. Its main function is to deliver messages regarding the received picture to specific recipients in the form of the corresponding areas of the brain. Any injury to this formation, regardless of severity, can lead to negative consequences.

eyeball chambers

Closed-type spaces in the eyeball are the so-called chambers. They contain intraocular moisture. There is a connection between them. There are two such formations. One is in the front position, and the other is in the back. The pupil acts as a link.

The anterior space is located just behind the corneal region. Its back side is limited by the iris. As for the space behind the iris, this is the rear chamber. The vitreous body serves as its support. The unchanging volume of chambers is the norm. The production of moisture and its outflow are processes that contribute to the adjustment of compliance with standard volumes. The production of eye fluid is possible due to the functionality of the ciliary processes. Its outflow is provided by a drainage system. It is located in the frontal part, where the cornea is in contact with the sclera.

The functionality of the chambers is to maintain "cooperation" between the intraocular tissues. They are also responsible for the flow of light fluxes to the retina. The rays of light at the entrance are refracted accordingly as a result of joint activity with the cornea. This is achieved through the properties of optics, inherent not only in the moisture inside the eye, but also in the cornea. Creates a lens effect.

The cornea, in part of its endothelial layer, acts as an external limiter for the anterior chamber. The border of the reverse side is formed by the iris and lens. The maximum depth falls on the area where the pupil is located. Its value reaches 3.5 mm. When moving to the periphery, this parameter slowly decreases. Sometimes this depth is greater, for example, in the absence of the lens due to its removal, or less if the choroid exfoliates.

The posterior space is limited in front by the leaf of the iris, and its back rests against the vitreous body. The equator of the lens acts as an internal limiter. The outer barrier forms the ciliary body. Inside there is a large number of zinn ligaments, which are thin threads. They create a formation that acts as a link between the ciliary body and the biological lens in the form of a lens. The shape of the latter is able to change under the influence of the ciliary muscle and the corresponding ligaments. This provides the required visibility of objects, regardless of their distance.

The composition of the moisture inside the eye correlates with the characteristics of the blood plasma. The intraocular fluid makes it possible to deliver the nutrients required to ensure the normal functioning of the organs of vision. Also with its help the possibility of removal of products of an exchange is realized.

The capacity of the chambers is determined by volumes in the range from 1.2 to 1.32 cm3. In this case, it is important how the production and outflow of eye fluid is performed. These processes require balance. Any disruption in the operation of such a system leads to negative consequences. For example, there is a possibility of development, which threatens with serious problems with the quality of vision.

The ciliary processes serve as sources of eye moisture, which is achieved by filtering the blood. The immediate place where the fluid is formed is the posterior chamber. After that, it moves to the anterior with a subsequent outflow. The possibility of this process is determined by the difference in pressure created in the veins. At the last stage, moisture is absorbed by these vessels.

Schlemm's channel

The gap inside the sclera, characterized as circular. Named after the German physician Friedrich Schlemm. The anterior chamber, in part of its angle, where the junction of the iris and cornea is formed, is a more precise area for the location of the Schlemm's canal. Its purpose is to remove aqueous humor with its subsequent absorption by the anterior ciliary vein.

The structure of the channel is more related to how the lymphatic vessel looks. Its inner part, which comes into contact with the generated moisture, is a mesh formation.

The channel's liquid transport capacity is 2 to 3 micro liters per minute. Injuries and infections block the channel, which provokes the appearance of a disease in the form of glaucoma.

Blood supply to the eye

Creating a flow of blood to the organs of vision is the functionality of the ophthalmic artery, which is an integral part of the structure of the eye. A corresponding branch is formed from the carotid artery. It reaches the eye opening and penetrates the orbit, which it does along with the optic nerve. Then its direction changes. The nerve bends around from the outside in such a way that the branch is on top. An arc is formed with muscular, ciliary and other branches emanating from it. The central artery provides blood supply to the retina. The vessels involved in this process form their own system. It also includes the ciliary arteries.

After the system is in the eyeball, it is divided into branches, which guarantees proper nutrition of the retina. Such formations are defined as terminal: they do not have connections with adjacent vessels.

Ciliary arteries are characterized by location. The posterior ones reach the back of the eyeball, bypass the sclera and diverge. The features of the front include the fact that they differ in length.

The ciliary arteries, defined as short, pass through the sclera and form a separate vascular formation consisting of many branches. At the entrance to the sclera, a vascular corolla is formed from the arteries of this type. It occurs where the optic nerve originates.

Ciliary arteries of smaller length also end up in the eyeball and rush to the ciliary body. In the frontal region, each such vessel splits into two stems. A formation with a concentric structure is created. After which they meet with similar branches of another artery. A circle is formed, defined as a large arterial. A similar formation of smaller sizes also occurs in the place where the ciliary and pupillary iris belt is located.

The ciliary arteries, characterized as anterior, are part of the muscular blood vessels of this type. They do not end in the area formed by the rectus muscles, but stretch further. There is an immersion in the episcleral tissue. First, the arteries pass along the periphery of the eyeball, and then go deep into it through seven branches. As a result, they connect with each other. A circle of blood circulation is formed along the perimeter of the iris, designated as a large one.

On the approach to the eyeball, a loopy network is formed, consisting of ciliary arteries. She entangles the cornea. There is also a division of non-branches that provide blood supply to the conjunctiva.

Partially, the outflow of blood is facilitated by the veins that go along with the arteries. This is mainly possible due to the venous pathways, which are collected in separate systems.

Whirlpool veins serve as a kind of collectors. Their function is to collect blood. The passage of these veins of the sclera occurs at an oblique angle. They provide blood flow. She enters the eye socket. The main collector of blood is the ophthalmic vein, which occupies the upper position. Through the corresponding gap, it is displayed in the cavernous sinus.

The ophthalmic vein below receives blood from the whirlpool veins passing in this place. It is splitting up. One branch connects to the ophthalmic vein located above, and the other reaches the deep vein of the face and the slit-like space with the pterygoid process.

Basically, the blood flow from the ciliary veins (anterior) fills such vessels of the orbit. As a result, the main volume of blood enters the venous sinuses. A reverse flow is created. The remaining blood moves forward and fills the veins of the face.

The orbital veins connect with the veins of the nasal cavity, facial vessels, and the ethmoid sinus. The largest anastomosis is formed by the veins of the orbit and face. Its border affects the inner corner of the eyelids and directly connects the ophthalmic vein and the facial vein.

Muscles of the eye

The possibility of good and three-dimensional vision is achieved when the eyeballs are able to move in a certain way. Here, the coordination of the work of the visual organs is of particular importance. The guarantors of this functioning are six muscles of the eye, where four of them are straight, and two are oblique. The latter are so called because of the peculiarity of the course.

The cranial nerves are responsible for the activity of these muscles. The fibers of the considered group of muscle tissue are maximally saturated with nerve endings, which determines their work from a position of high accuracy.

Through the muscles responsible for the physical activity of the eyeballs, diverse movements are available. The need to implement this functionality is determined by the fact that the coordinated work of this type of muscle fibers is required. The same pictures of objects should be fixed on the same areas of the retina. This allows you to feel the depth of space and see perfectly.

The structure of the muscles of the eye

The muscles of the eye begin near the ring, which serves as the environment of the optic canal close to the external opening. The only exception concerns oblique muscle tissue, which occupies the lower position.

The muscles are arranged so that they form a funnel. Nerve fibers and blood vessels pass through it. As you move away from the beginning of this formation, the oblique muscle located at the top deviates. There is a shift towards a kind of block. Here it is transformed into a tendon. Passing through the block loop sets the direction at an angle. The muscle is attached to the upper iris of the eyeball. The oblique muscle (lower) also begins there, from the edge of the orbit.

As the muscles approach the eyeball, a dense capsule (Tenon's membrane) is formed. A connection is established with the sclera, which occurs with varying degrees of distance from the limbus. At the minimum distance, the internal rectus muscle is located, at the maximum distance, the upper one. The oblique muscles are fixed closer to the center of the eyeball.

The function of the oculomotor nerve is to maintain the proper functioning of the muscles of the eye. The responsibility of the abducens nerve is determined by maintaining the activity of the rectus muscle (external), and the trochlear - by the superior oblique. The regulation of this type is characterized by its own peculiarity. A small number of muscle fibers are controlled by one branch of the motor nerve, which significantly increases the clarity of eye movements.

The nuances of muscle attachment set the variability of exactly how the eyeballs are able to move. The rectus muscles (internal, external) are attached in such a way that they are provided with horizontal rotations. The activity of the internal rectus muscle allows you to turn the eyeball towards the nose, and the external one - to the temple.

The rectus muscles are responsible for vertical movements. There is a nuance to their location, due to the fact that there is a certain slope of the fixation line, if you focus on the limbus line. This circumstance creates conditions when, together with the vertical movement, the eyeball turns inward.

The functioning of the oblique muscles is more complex. This is explained by the peculiarities of the location of this muscle tissue. Lowering the eye and turning outward is provided by the oblique muscle located at the top, and lifting, including turning outward, is also an oblique muscle, but already lower.

Another of the capabilities of the muscles mentioned is the provision of minor rotations of the eyeball in accordance with the movement of the clock hand, regardless of direction. Regulation at the level of maintaining the desired activity of nerve fibers and the coherence of the work of the eye muscles are two points that contribute to the implementation of complex turns of the eyeballs of any direction. As a result, vision acquires such a property as volume, and its clarity increases significantly.

Shells of the eye

The shape of the eye is held by the appropriate shells. Although the functionality of these formations is not limited to this. With their help, the delivery of nutrients is carried out, and the process is supported (clear vision of objects when the distance to them changes).

The organs of vision are distinguished by a multilayer structure, manifested in the form of the following shells:

fibrous;
vascular;
retina.

Fibrous membrane of the eye

Connective tissue that allows you to hold a specific shape of the eye. It also acts as a protective barrier. The structure of the fibrous membrane suggests the presence of two components, where one is the cornea, and the second is the sclera.

Cornea

A shell characterized by transparency and elasticity. The shape corresponds to a convex-concave lens. The functionality is almost identical to what a camera lens does: it focuses rays of light. The concave side of the cornea looks back.

The composition of this shell is formed by five layers:

epithelium;
Bowman's membrane;
stroma;
Descemet's membrane;
endothelium.

Sclera

The external protection of the eyeball plays an important role in the structure of the eye. Forms a fibrous membrane, which also includes the cornea. Unlike the latter, the sclera is an opaque tissue. This is due to the chaotic arrangement of collagen fibers.

The main function is high-quality vision, which is guaranteed due to the obstruction of the penetration of light rays through the sclera.

The possibility of blindness is excluded. Also, this formation serves as a support for the components of the eye, which are placed outside the eyeball. These include nerves, vessels, ligaments and oculomotor muscles. The density of the structure ensures the maintenance of intraocular pressure within the specified values. The helmet canal acts as a transport channel that provides an outflow of eye moisture.

choroid

It is formed on the basis of three parts:

iris;
ciliary body;
choroid.

iris

Part of the choroid, which differs from other departments of this formation in that its location is frontal versus parietal, if you focus on the plane of the limbus. Represents a disk. In the center is a hole known as the pupil.

Structurally consists of three layers:

border, located in front;
stromal;
pigment-muscular.

Fibroblasts are involved in the formation of the first layer, connecting with each other through their processes. Behind them are pigment-containing melanocytes. The color of the iris depends on the number of these specific skin cells. This trait is inherited. The brown iris is dominant in terms of inheritance, and the blue iris is recessive.

In the bulk of newborns, the iris has a light blue tint, which is due to poorly developed pigmentation. Closer to six months of age, the color becomes darker. This is due to an increase in the number of melanocytes. The absence of melanosomes in albinos leads to the dominance of pink. In some cases, it is possible when the eyes in the part of the iris get a different color. Melanocytes are capable of provoking the development of melanomas.

Further immersion in the stroma reveals a network consisting of a large number of capillaries and collagen fibers. The distribution of the latter captures the muscles of the iris. There is a connection with the ciliary body.

The back layer of the iris consists of two muscles. The pupillary sphincter, shaped like a ring, and the dilator, which has a radial orientation. The functioning of the first is provided by the oculomotor nerve, and the second - by the sympathetic. The pigment epithelium is also present here as part of an undifferentiated area of the retina.

The thickness of the iris varies depending on the specific area of this formation. The range of such changes is 0.2–0.4 mm. The minimum thickness is observed in the root zone.

The center of the iris is occupied by the pupil. Its width is changeable under the influence of light, which is provided by the corresponding muscles. High illumination provokes contraction, and less illumination provokes expansion.

The iris in part of its anterior surface is divided into pupillary and ciliary zones. The width of the first is 1 mm and the second - from 3 to 4 mm. The distinction in this case provides a kind of roller, which has a toothed shape. The muscles of the pupil are distributed as follows: the sphincter is the pupillary belt, and the dilator is the ciliary.

The ciliary arteries, which form a large arterial circle, deliver blood to the iris. The small arterial circle also participates in this process. The innervation of this particular zone of the choroid is achieved by the ciliary nerves.

ciliary body

The area of the choroid responsible for the production of eye fluid. The name ciliary body is also used.
The structure of the formation in question is muscle tissue and blood vessels. The muscular content of this shell suggests the presence of several layers with different directions. Their activity includes the work of the lens. Its form is changing. As a result, a person gets the opportunity to clearly see objects at different distances. Another functionality of the ciliary body is to retain heat.

The blood capillaries located in the ciliary processes contribute to the production of intraocular moisture. Blood flow is filtered. Moisture of this kind ensures the proper functioning of the eye. The intraocular pressure is kept constant.

Also, the ciliary body serves as a support for the iris.

Choroidea (Choroidea)

The area of the vascular tract, located behind. The limits of this shell are limited to the optic nerve and the dentate line.
The parameter thickness of the posterior pole is from 0.22 to 0.3 mm. When approaching the dentate line, it decreases to 0.1–0.15 mm. The choroid in part of the vessels consists of ciliary arteries, where the posterior short ones go towards the equator, and the anterior ones go towards the choroid, when the connection of the second with the first is achieved in its anterior region.

The ciliary arteries bypass the sclera and reach the suprachoroidal space bounded by the choroid and sclera. There is a disintegration into a significant number of branches. They become the basis of the choroid. The vascular circle of Zinn-Galera is formed along the perimeter of the optic disc. Sometimes there may be an additional branch in the macula. It is visible either on the retina or on the optic disc. An important point in embolism of the central retinal artery.

The vascular membrane includes four components:

supravascular with dark pigment;
vascular brownish tint;
vascular-capillary, supporting the work of the retina;
basal layer.

The retina of the eye (retina)

The retina is a peripheral section that launches the visual analyzer, which plays an important role in the structure of the human eye. With its help, light waves are captured, they are converted into impulses at the level of excitation of the nervous system, and further information is transmitted through the optic nerve.

The retina is the nerve tissue that forms the eyeball in part of its inner shell. It limits the space filled with the vitreous body. The choroid acts as an outer frame. The thickness of the retina is insignificant. The parameter corresponding to the norm is only 281 microns.

The surface of the eyeball from the inside is mostly covered with retina. The beginning of the retina can conditionally be considered the ONH. Further, it stretches to such a border as a jagged line. Then it is transformed into the pigment epithelium, envelops the inner shell of the ciliary body and spreads to the iris. The optic disc and the dentate line are areas where the attachment of the retina is most secure. In other places, its connection is characterized by low density. It is this fact that explains why the fabric peels off easily. This causes a lot of serious problems.

The structure of the retina is formed by several layers with different functionality and structure. They are closely connected to each other. A tight contact is formed, which determines the creation of what is commonly called a visual analyzer. Through it, a person is given the opportunity to correctly perceive the world around him, when an adequate assessment of the color, shape and size of objects, as well as the distance to them is made.

Rays of light, when they enter the eye, pass through several refractive media. Under them should be understood the cornea, eye fluid, the transparent body of the lens and the vitreous body. If the refraction is within the normal range, then as a result of such a passage of light rays, a picture of objects that fall into the field of view is formed on the retina. The resulting image differs in that it is inverted. Further, certain parts of the brain receive the appropriate impulses, and a person acquires the ability to see what surrounds him.

From the point of view of the structure of the retina - the most complex formation. All its components closely interact with each other. It is multi-layered. Damage to any layer can lead to a negative outcome. Visual perception as the functionality of the retina is provided by a three-neural network that conducts excitations from receptors. Its composition is formed by a wide set of neurons.

Retinal layers

Retina forms a "sandwich" of ten rows:

1. pigment epithelium adjacent to Bruch's membrane. Differs in wide functionality. Protection, cellular nutrition, transportation. It accepts the rejecting segments of photoreceptors. Serves as a barrier to light radiation.

2. photosensor layer. Cells that are sensitive to light, in the form of a kind of rods and cones. The rod-like cylinders contain the visual segment rhodopsin, and the cones contain iodopsin. The first provides color perception and peripheral vision, and the second provides vision in low light.

3. Boundary membrane(outer). Structurally, it consists of terminal formations and external sections of retinal receptors. The structure of Müllerian cells, due to their processes, makes it possible to collect light on the retina and deliver it to the appropriate receptors.

4. nuclear layer(outer). It got its name due to the fact that it is formed on the basis of the nuclei and bodies of light-sensitive cells.

5. Plexiform layer(outer). Determined by contacts at the cell level. Occur between neurons characterized as bipolar and associative. This also includes light-sensitive formations of this type.

6. nuclear layer(interior). Formed from different cells, for example, bipolar and Müllerian. The demand for the latter is associated with the need to maintain the functions of the nervous tissue. Others are focused on signal processing from photoreceptors.

7. Plexiform layer(interior). Interlacing of nerve cells in part of their processes. Serves as a separator between the inner part of the retina, characterized as vascular, and the outer - avascular.

8. ganglion cells. Provide free penetration of light due to the lack of such a coating as myelin. They act as a bridge between light-sensitive cells and the optic nerve.

9. ganglion cell. Participates in the formation of the optic nerve.

10. Boundary membrane(internal). Retina coating on the inside. Consists of Muller cells.

Optical system of the eye

The quality of vision depends on the main parts of the human eye. The condition of the transmissive in the form of the cornea, retina and lens directly affects how a person will see: good or bad.

The cornea takes a greater part in the refraction of light rays. In this context, we can draw an analogy with the principle of operation of the camera. The diaphragm is the pupil. With its help, the flow of light rays is regulated, and the focal length sets the image quality.

Thanks to the lens, light rays fall on the "film". In our case, it should be understood as the retina.

The vitreous body and moisture in the eye chambers also refract light rays, but to a much lesser extent. Although the state of these formations significantly affects the quality of vision. It can worsen with a decrease in the degree of transparency of moisture or the appearance of blood in it.

The correct perception of the surrounding world through the organs of vision assumes that the passage of light rays through all optical media leads to the formation on the retina of a reduced and inverted image, but real. The final processing of information from the visual receptors occurs in the brain regions. The occipital lobes are responsible for this.

lacrimal apparatus

Physiological system that provides the production of special moisture with its subsequent withdrawal into the nasal cavity. The organs of the lacrimal system are classified depending on the secretory department and the lacrimal apparatus. The peculiarity of the system lies in the pairing of its organs.

The job of the end section is to produce a tear. Its structure includes the lacrimal gland and additional formations of a similar kind. The first refers to the serous gland, which has a complex structure. It is divided into two parts (bottom, top), where the tendon of the muscle responsible for lifting the upper eyelid acts as a separating barrier. The area at the top in terms of size is as follows: 12 by 25 mm at 5 mm thick. Its location is determined by the wall of the orbit, which has an upward and outward orientation. This part includes the excretory tubules. Their number varies from 3 to 5. The output is carried out in the conjunctiva.

As for the lower part, it has a smaller size (11 by 8 mm) and a smaller thickness (2 mm). She has tubules, where some connect with the same formations of the upper part, while others are removed into the conjunctival sac.

The lacrimal gland is supplied with blood through the lacrimal artery, and the outflow is organized into the lacrimal vein. The trigeminal facial nerve acts as the initiator of the corresponding excitation of the nervous system. Sympathetic and parasympathetic nerve fibers are also connected to this process.

In a standard situation, only accessory glands work. Through their functionality, the production of tears in a volume of about 1 mm is ensured. This provides the required hydration. As for the main lacrimal gland, it comes into action when various kinds of irritants appear. These can be foreign bodies, too bright light, emotional outburst, etc.

The structure of the lacrimal division is based on formations that promote the movement of moisture. They are also responsible for its withdrawal. This functioning is provided by the lacrimal stream, lake, points, tubules, sac and nasolacrimal duct.

The mentioned points are perfectly visualized. Their location is determined by the inner corners of the eyelids. They are oriented towards the lacrimal lake and are in close contact with the conjunctiva. The establishment of a connection between the bag and the points is achieved through special tubules, reaching a length of 8–10 mm.

The location of the lacrimal sac is determined by the bony fossa located near the angle of the orbit. From the point of view of anatomy, this formation is a closed cavity of a cylindrical type. It is extended by 10 mm, and its width is 4 mm. On the surface of the bag there is an epithelium, which has a goblet glandulocyte in its composition. Blood inflow is provided by the ophthalmic artery, and the outflow is provided by small veins. Part of the sac below communicates with the nasolacrimal canal, which opens into the nasal cavity.

vitreous body

Gel-like substance. Fills the eyeball by 2/3. Differs in transparency. Consists of 99% water, which contains hyaluronic acid.

There is a notch in the front. It is attached to the lens. Otherwise, this formation is in contact with the retina in part of its membrane. The optic disc and the lens are related through the hyaloid canal. Structurally, the vitreous body is composed of collagen protein in the form of fibers. The existing gaps between them are filled with liquid. This explains that the formation in question is a gelatinous mass.

On the periphery are hyalocytes - cells that contribute to the formation of hyaluronic acid, proteins and collagens. They are also involved in the formation of protein structures known as hemidesmosomes. With their help, a tight connection is established between the retinal membrane and the vitreous body itself.

The main functions of the latter include:

giving the eye a specific shape;
refraction of light rays;
creation of a certain tension in the tissues of the organ of vision;
achieving the effect of incompressibility of the eye.

Photoreceptors

The type of neurons that make up the retina of the eye. Provide processing of the light signal in such a way that it is converted into electrical impulses. This triggers biological processes that lead to the formation of visual images. In practice, photoreceptor proteins absorb photons, which saturate the cell with the appropriate potential.

Light-sensitive formations are peculiar rods and cones. Their functionality contributes to the correct perception of objects of the external world. As a result, we can talk about the formation of the corresponding effect - vision. A person is able to see due to the biological processes occurring in such parts of the photoreceptors as the outer lobes of their membranes.

There are also light-sensitive cells known as the eyes of Hesse. They are located inside the pigment cell, which has a cup-shaped shape. The work of these formations is to capture the direction of the rays of light and determine its intensity. With their help, the light signal is processed when electrical impulses are obtained at the output.

The next class of photoreceptors became known in the 1990s. It refers to the light-sensitive cells of the ganglionic layer of the retina. They support the visual process, but in an indirect way. This refers to biological rhythms during the day and the pupillary reflex.

The so-called rods and cones differ significantly from each other in terms of functionality. For example, the first is characterized by high sensitivity. If the lighting is low, then it is they who guarantee the formation of at least some kind of visual image. This fact makes it clear why colors are poorly distinguished in low light. In this case, only one type of photoreceptors, rods, is active.

The cones need brighter light to work, to allow the appropriate biological signals to pass through. The structure of the retina suggests the presence of different types of cones. There are three in total. Each defines photoreceptors tuned to a particular wavelength of light.

For the perception of a picture in color, the cortical regions are responsible for processing visual information, which implies the recognition of impulses in the RGB format. Cones are able to distinguish light flux by wavelength, characterizing them as short, medium and long. Depending on how many photons the cone is able to absorb, corresponding biological reactions are formed. The various responses of these formations are based on a specific number of photons of one or another length taken in. In particular, the photoreceptor proteins of L-cones absorb the conventional red color associated with long wavelengths. Light rays of shorter length are capable of producing the same response if they are bright enough.

The reaction of the same photoreceptor can be provoked by light waves of different lengths, when differences are also observed at the intensity level of the light flux. As a result, the brain does not always determine the light and the resulting image. Through the visual receptors, the selection and selection of the brightest rays occurs. Then, biosignals are formed that enter those parts of the brain where information of this type is processed. A subjective perception of the optical image in color is created.

The human retina consists of 6 million cones and 120 million rods. In animals, their number and ratio is different. The main influence is the lifestyle. In owls, the retina contains a very significant number of rods. The human visual system is almost 1.5 million ganglion cells. Among them there are cells with photosensitivity.

lens

A biological lens characterized in terms of shape as biconvex. It acts as an element of the light-conducting and light-refracting system. Provides the ability to focus on objects at different distances. Located in the posterior chamber of the eye. The height of the lens is 8 to 9 mm and its thickness is 4 to 5 mm. With age, it thickens. This process is slow but sure. The anterior part of this transparent body has a less convex surface than the posterior one.

The shape of the lens corresponds to a biconvex lens having a radius of curvature in the anterior part of about 10 mm. At the same time, on the reverse side, this parameter does not exceed 6 mm. The lens diameter is 10 mm, and the size in the anterior part is from 3.5 to 5 mm. The substance contained inside is held by a thin-walled capsule. The front part has epithelial tissue located below. There is no epithelium on the back side of the capsule.

Epithelial cells differ in that they are constantly dividing, but this does not affect the volume of the lens in terms of its change. This situation is explained by the dehydration of old cells located at a minimum distance from the center of the transparent body. This helps to reduce their volume. The process of this type leads to such features as age. When a person reaches the age of 40, the elasticity of the lens is lost. The accommodation reserve is reduced, and the ability to see well at close range is significantly worsened.

The lens is located directly behind the iris. Its retention is provided by thin threads that form a zinn ligament. One of their ends enters the lens shell, and the other is fixed on the ciliary body. The degree of tension of these threads affects the shape of the transparent body, which changes the refractive power. As a result, the process of accommodation becomes possible. The lens serves as the boundary between two sections: anterior and posterior.

The following functionality of the lens is distinguished:

light transmission - achieved due to the fact that the body of this element of the eye is transparent;
light refraction - works like a biological lens, acts as a second refractive medium (the first is the cornea). At rest, the refractive power parameter is 19 diopters. This is the norm;
accommodation - a change in the shape of a transparent body in order to have a good vision of objects located at different distances. The refractive power in this case varies in the range from 19 to 33 diopters;
division - forms two sections of the eye (anterior, posterior), which is determined by the location. Acts as a barrier that holds back the vitreous body. It cannot be in the anterior chamber;
protection - biological safety is ensured. Pathogenic microorganisms, once in the anterior chamber, are not able to penetrate the vitreous body.

Congenital diseases in some cases lead to displacement of the lens. It occupies the wrong position due to the fact that the ligamentous apparatus is weakened or has some structural defect. This also includes the likelihood of congenital opacities of the nucleus. All this contributes to a decrease in vision.

Zinn's bunch

Formation based on fibers, defined as glycoprotein and zonular. Provides fixation of the lens. The surface of the fibers is coated with a mucopolysaccharide gel, which is due to the need for protection from moisture present in the chambers of the eye. The space behind the lens serves as the place where this formation is located.

The activity of the ligament of zon leads to contraction of the ciliary muscle. The lens changes curvature, which allows you to focus on objects at different distances. Muscle tension loosens the tension, and the lens takes on a shape close to a ball. Relaxation of the muscle leads to tension in the fibers, which flattens the lens. Focus changes.

The considered fibers are divided into posterior and anterior. One side of the posterior fibers is attached at the serrated edge, and the other side is attached to the frontal region of the lens. The starting point of the anterior fibers is the base of the ciliary processes, and the attachment is carried out in the back of the lens and closer to the equator. Crossed fibers contribute to the formation of a slit-like space along the periphery of the lens.

The fibers are attached to the ciliary body in part of the vitreous membrane. In the case of detachment of these formations, the so-called dislocation of the lens, due to its displacement, is ascertained.

The ligament of Zinn acts as the main element of the system that provides the possibility of accommodation of the eye.

Video

Eyeball

The eyeball is spherical in shape. It has anterior and posterior poles. The anterior pole is the most protruding point of the cornea, the posterior one is located from the exit point of the optic nerve. The conditional line connecting both poles is called the axis of the eye.

The eyeball consists of a core covered with three membranes: fibrous, vascular and internal, or reticular.

Outside, the eyeball is covered with a fibrous membrane, which is subdivided into the posterior section - the sclera and the transparent anterior - the cornea, the border between which runs along the scleral groove.

Behind the sclera is a cribriform plate through which the fibers of the optic nerve pass.

The cornea is a transparent convex saucer-shaped plate, consisting of five layers: anterior epithelium, anterior border plate, own substance (cornea), posterior border plate, posterior epithelium (corneal endothelium). The cornea is devoid of blood vessels, its nutrition occurs due to diffusion from the vessels of the limbus and the fluid of the anterior chamber of the eye.

Ahead, the choroid passes into a thickened ciliary body of an annular shape. The ciliary body is involved in the accommodation of the eye, supporting, fixing and stretching the lens. The ciliary body in front passes into the iris, which is a round disk with a hole in the center (pupil). The iris is located between the cornea and the lens.

The iris consists of five layers: the anterior - the epithelium - is a continuation of the epithelium covering the posterior surface of the cornea, followed by the outer boundary layer, the vascular layer, the inner boundary layer and the pigment layer lining the posterior surface.

The outer boundary layer is formed by the main substance, in which there are many fibroblasts and pigment cells. The vascular layer consists of loose fibrous connective tissue, which contains numerous vessels and pigment cells.

The inner (boundary) layer of the iris is similar in structure to the outer. The pigment layer of the iris is a continuation of the epithelium covering the ciliary body and ciliary processes, it is two-layered. The different quantity and quality of the melanin pigment determines the color of the eyes - brown, black (if there is a large amount of melanin), blue, greenish (if there is little pigment). The iris is 12 to 13 mm in diameter and about three-tenths of a millimeter thick. It has two circles - large and small.

The layers of the iris are as follows:

Endothelium

This layer is formed by complex cells that are responsible for contact with the aqueous humor (the fluid that is in the anterior part of the eye).

Stroma

This is the actual tissue of the iris of the eye, which consists of connective tissue, chromatic cells, muscle veins, nerve fibers, blood vessels, lymphatic vessels and a basilar membrane with a deep layer that contains a millimeter-wide annular border of muscle veins, the contraction of which reduces the size of the pupil ( sphincter).

Pigmentation layer

Consists of two rows of dark purple epithelial cells.

These are retinal epithelial cells that are located above the small circle of the iris and surround the pupil.

The innervation of the iris consists of a large neuroglandular autonomic system with sympathetic thoracolumbar regions and parasympathetic regions of the skull and pelvis.

The annular muscle fibers, as well as the ciliary muscle, are innervated by the section of the short ciliary nerve of the general motor system of the eye (III nerve), which is associated with the mesencephalic section.

The dilatory muscle fibers are innervated by the long ciliary nerve, which is associated with the sympathetic cervical ganglion.

These nerves pass to the iris through the layer of the shell of the eyeball, forming the iridological plexus, from where they are directed to muscle fibers and other structures of the iris. Some nerve fibers form a network, or chain, on the subendothelial surface. This chain consists of triangular cells whose bases describe concentric circles. Thus, there is a deep mobile chain of nerve fibers.

If we consider everything in a complex, then we can conclude that the iris is the most sensitive organ of the body: if the muscles of the legs correspond to 120 muscle fibers per unit, then the muscles of the iris correspond to from one to eight fibers per unit, which is a huge figure for such a small anatomical space.