The eyeball has 2 poles: back and front. The average distance between them is 24 mm. It is the largest size of the eyeball. The bulk of the latter is the inner core. It is transparent content surrounded by three shells. It consists of aqueous humor, a lens and the following three eye membranes surround the nucleus of the eyeball on all sides: fibrous (outer), vascular (middle) and reticular (inner). Let's talk about each of them.
Outer sheath
The most durable is the outer shell of the eye, fibrous. It is thanks to her that the eyeball is able to maintain its shape.
Cornea
The cornea, or cornea, is its smaller, anterior section. Its size is about 1/6 the size of the entire shell. The cornea in the eyeball is the most convex part of it. In appearance, it is a concave-convex, somewhat elongated lens, which is turned backward by a concave surface. Approximately 0.5 mm is the approximate thickness of the cornea. Its horizontal diameter is 11-12 mm. As for the vertical one, its size is 10.5-11 mm.
The cornea is the transparent membrane of the eye. It contains a transparent connective tissue stroma, as well as corneal corpuscles, which form its own substance. The posterior and anterior boundary plates adjoin the stroma from the posterior and anterior surfaces. The latter is the main substance of the cornea (modified), while the other is a derivative of the endothelium, which covers its posterior surface and also lines the entire anterior chamber of the human eye. The stratified epithelium covers the anterior surface of the cornea. It passes without sharp boundaries into the epithelium of the connective membrane. Due to the homogeneity of the tissue, as well as the absence of lymphatic and blood vessels, the cornea, unlike the next layer, which is the white membrane of the eye, is transparent. We now turn to the description of the sclera.
Sclera
The white membrane of the eye is called the sclera. This is the larger, posterior part of the outer shell, making up about 1/6 of it. The sclera is a direct continuation of the cornea. However, it is formed, in contrast to the latter, by fibers of connective tissue (dense) with an admixture of other fibers - elastic. The white membrane of the eye, moreover, is opaque. The sclera passes into the cornea gradually. The translucent rim is on the border between them. It is called the edge of the cornea. Now you know what the white of the eye is. It is transparent only at the very beginning, near the cornea.
Scleral divisions
In the anterior section, the outer surface of the sclera is covered with the conjunctiva. These are the eyes. Otherwise, it is called connective tissue. As for the posterior part, here it is covered only by the endothelium. The endothelium also covers the inner surface of the sclera, which faces the choroid. The sclera is not the same thickness throughout its entire length. The thinnest area is the place where the fibers of the optic nerve penetrate it, which leaves the eyeball. A lattice plate is formed here. The sclera is thickest precisely in the circumference of the optic nerve. It is here from 1 to 1.5 mm. Then the thickness decreases, reaching 0.4-0.5 mm at the equator. Moving to the area of \u200b\u200bmuscle attachment, the sclera thickens again, its length here is about 0.6 mm. Not only fibers of the optic nerve pass through it, but also venous and arterial vessels, as well as nerves. They form a series of holes in the sclera, which are called scleral graduates. Near the edge of the cornea, in the depths of its anterior section, lies the scleral sinus along its entire length, running circularly.
Choroid
So, we have briefly characterized the outer shell of the eye. We now turn to the characteristic of the vascular, which is also called the average. It is divided into the following 3 unequal parts. The first of them is large, posterior, which lines about two-thirds of the inner surface of the sclera. It is called the choroid itself. The second part is the middle, located on the border between the cornea and the sclera. This is Finally, the third part (smaller, front), which shines through the cornea, is called the iris, or iris.
The choroid itself passes without sharp boundaries in the anterior sections into the ciliary body. The jagged edge of the wall can act as a border between them. Almost throughout the entire choroid itself, the choroid itself only adjoins the sclera, except for the spot area, as well as the area that corresponds to the optic nerve head. The choroid in the region of the latter has an optic opening through which the fibers of the optic nerve exit to the ethmoid plate of the sclera. Its outer surface on the rest of the length is covered with pigment and It limits the perivascular capillary space together with the inner surface of the sclera.
Other layers of the membrane of interest to us are formed from the layer of large vessels that form the vascular plate. These are mainly veins and also arteries. Connective tissue elastic fibers, as well as pigment cells are located between them. The layer of middle vessels lies deeper than this layer. It is less pigmented. Adjacent to it is a network of small capillaries and vessels, which forms the vascular-capillary plate. It is especially developed in the area of \u200b\u200bthe macula. The structureless fibrous layer is the deepest zone of the choroid itself. It is called the main plate. In the anterior section, the choroid thickens slightly and passes without sharp boundaries into the ciliary body.
Ciliary body
It is covered from the inner surface with a main plate, which is a continuation of the leaf. The leaf refers to the choroid itself. The ciliary body for the most part consists of the ciliary muscle, as well as the stroma of the ciliary body. The latter is represented by connective tissue, rich in pigment cells and loose, as well as many vessels.
The following parts are distinguished in the ciliary body: ciliary circle, ciliary corolla and ciliary muscle. The latter occupies its outer section and is adjacent directly to the sclera. The ciliary muscle is formed by smooth muscle fibers. Among them, circular and meridian fibers are distinguished. The latter are highly developed. They form a muscle that serves to stretch the choroid itself. From the sclera and the angle of the anterior chamber, its fibers begin. Heading posteriorly, they are gradually lost in the choroid. This muscle, contracting, pulls forward the ciliary body (back part) and the choroid itself (front part). This reduces the tension of the ciliary band.
Ciliary muscle
Circular fibers are involved in the formation of the circular muscle. Its contraction reduces the lumen of the ring, which is formed by the ciliary body. Due to this, the place of fixation to the equator of the lens of the ciliary girdle approaches. This causes the belt to relax. In addition, the curvature of the lens increases. It is because of this that the circular part of the ciliary muscle is also called the muscle that compresses the lens.
Ciliary circle
This is the posterior-inner part of the ciliary body. It is arched in shape and has an uneven surface. The ciliary circle continues without sharp boundaries in the choroid itself.
Ciliary corolla
It occupies the anterior-inner part. In it, small folds are distinguished, running radially. These ciliary folds pass anteriorly into the ciliary processes, of which there are about 70, and which hang freely in the region of the posterior chamber of the apple. The rounded edge is formed at the point where there is a transition to the ciliary corolla of the ciliary circle. This is the place of attachment of the ciliary girdle fixing lens.
Iris
The front section is the iris, or iris. Unlike other divisions, it does not adjoin directly to the fibrous sheath. The iris is a continuation of the ciliary body (its anterior section). It is located in and somewhat removed from the cornea. A round hole called the pupil is located in its center. The ciliary edge is the opposite edge that runs along the entire circumference of the iris. The thickness of the latter consists of smooth muscles, blood vessels, connective tissue, and many nerve fibers. The pigment that determines the "color" of the eye is the cells of the back surface of the iris.
Its smooth muscles are in two directions: radial and circular. A circular layer lies around the pupil. It forms a muscle that constricts the pupil. The fibers, located radially, form the muscle, which expands it.
The anterior surface of the iris is slightly convex anteriorly. Accordingly, the back is concave. On the front, in the circumference of the pupil, there is an inner small ring of the iris (pupillary belt). Its width is about 1 mm. The small ring is limited from the outside by an irregular toothed line running circularly. It is called the small circle of the iris. The rest of its anterior surface is about 3-4 mm wide. It belongs to the outer large ring of the iris, or ciliary part.
Retina
We have not considered all the membranes of the eye yet. We presented fibrous and vascular. Which eye membrane has not yet been considered? The answer is internal, reticular (also called retina). This sheath is represented by nerve cells arranged in several layers. It lines the eye from the inside. The significance of this shell of the eye is great. It is she who provides a person with vision, since objects are displayed on it. Then information about them is transmitted to the brain via the optic nerve. However, the retina does not all see the same way. The structure of the eye membrane is such that the macula is characterized by the greatest visual ability.
Macula
It represents the central part of the retina. We all heard from school that there are in the retina, but in the macula there are only cones, which are responsible for color vision. If it were not for her, we could not distinguish between small details, read. The macula has all the conditions for registering light rays in the most detailed way. The retina in this area becomes thinner. This allows the light rays to directly strike the light-sensitive cones. There are no retinal vessels in the macula that can interfere with clear vision. Its cells receive nutrition from the choroid deeper. Macula is the central part of the retina of the eye, where the main number of cones (visual cells) is located.
What's inside the shells
The anterior and posterior chambers (between the lens and the iris) are located inside the shells. They are filled with liquid inside. The vitreous body and the lens are located between them. The latter is a biconvex lens in shape. The lens, like the cornea, refracts and transmits light rays. This focuses the image on the retina. The vitreous body is of the consistency of jelly. separated from the lens with the help of it.
Each person is interested in anatomical issues, because they relate to the human body. Many people are interested in what the organ of vision consists of. After all, it belongs to the senses.
With the help of the eye, a person receives 90% of the information, the remaining 9% goes to hearing and 1% to other organs.
The most interesting topic is the structure of the human eye, the article describes in detail what the eyes are made of, what diseases are and how to cope with them.
What is the human eye?
Millions of years ago, one of the unique devices was created - this human eye... It consists of a subtle as well as a complex system.
The organ's task is to convey to the brain the information received and then processed. A person is helped by everything that happens to see the electromagnetic radiation of visible light, this perception affects every eye cell.
Its functions
The organ of vision has a special task, it consists of the following factors:
Eye structure
The visual organ is simultaneously covered by several membranes that are located around the inner nucleus of the eye. It consists of aqueous humor, as well as vitreous humor and lens.
The organ of vision has three shells:
- The first includes the outside. The muscles of the eyeball are adjacent to it, and it has a high density. It is equipped with a protective function and is responsible for the formation of the eye. The structure includes the cornea along with the sclera.
- The middle shell has another name - vascular. Its task lies in metabolic processes, thanks to this, the eye is nourished. It includes the iris, as well as the ciliary body with the choroid. The pupil takes center stage.
- The inner shell is otherwise called mesh. It belongs to the receptor part of the organ of vision, it is responsible for the perception of light, and also transmits information to the central nervous system.
Eyeball and optic nerve
A spherical body is responsible for the visual function - this eyeball... It receives all the information from the environment.
Responsible for the second pair of head nerves optic nerve... It starts from the lower surface of the brain, then smoothly turns into a cross, up to this point a part of the nerve has its own name - tractus opticus, after the cross it has a different name - n.opticus.
Eyelids
There are movable folds around the human organs of vision - the eyelids.
They serve several functions:
Thanks to the eyelids, the cornea and conjunctiva are equally hydrated.
Movable folds consist of two layers:
- Surface - it includes the skin along with the subcutaneous muscles.
- Deep - it includes cartilage, as well as the conjunctiva.
These two layers are separated by a grayish line, it is located at the edge of the folds, in front of it there is a large number of meibomian gland holes.
The task of the lacrimal apparatus is to produce tears and perform the function of drainage.
Its composition:
- lacrimal gland - is responsible for the release of tears, it controls the excretory ducts that push fluid to the surface of the organ of vision;
- lacrimal and nasolacrimal canals, lacrimal sac, they are necessary to drain fluid into the nose;
Muscles of the eye
The quality and volume of vision is ensured by the movement of the eyeball. The eye muscles in the amount of 6 pieces are responsible for this. The 3 cranial nerves control the functioning of the eye muscles.
The external structure of the human eye
The organ of vision consists of several important additional organs.
Cornea
Cornea - looks like a watch glass and represents the outer shell of the eye, it is transparent. It is the main one for the optical system. The cornea looks like a convex-concave lens; it is a small fraction of the envelope of the organ of vision. It has a transparent appearance, so it easily perceives light rays, reaching the retina itself.
Due to the presence of the limbus, the cornea passes into the sclera. The shell has different thicknesses, it is thin in the very center, thickening is observed in the transition to the periphery. The curvature in the radius is 7.7 mm, the radius of the horizontal diameter is 11 mm. And the refractive power is 41 diopters.
The cornea has 5 layers:
Conjunctiva
The eyeball is surrounded by an outer cover - a mucous membrane, it is called conjunctiva.
In addition, the shell is located in the inner surface of the eyelids, due to this, the vaults are formed above the eye and below.
Blind pockets are called vaults, due to which the eyeball moves easily. The upper vault has larger dimensions than the lower.
The conjunctiva plays a major role - they do not allow external factors to penetrate the organs of vision, while providing comfort. This is helped by numerous glands that produce mucin, as well as lacrimal glands.
A stable tear film is formed after the production of mucin, as well as lacrimal fluid, due to this, the eyes are protected and moisturized. If diseases appear on the conjunctiva, they are accompanied by unpleasant discomfort, the patient feels a burning sensation and the presence of a foreign body or sand in the eyes.
Conjunctival structure
The mucous membrane is thin and transparent in appearance and represents the conjunctiva. It is located on the back of the eyelids and has a tight connection with the cartilage. After the shell, special vaults are formed, among them there are upper and lower ones.
Internal structure of the eyeball
The inner surface is lined with a special retina, in another way it is called inner shell.
It looks like a 2 mm thick plate.
The retina is the visual portion as well as the blind area.
In most of the eyeball, the visual area is located, it contacts the choroid and is presented in the form of 2 layers:
- outer - the pigment layer belongs to it;
- internal - consists of nerve cells.
Due to the presence of a blind area, the ciliated body is covered, as well as the back of the iris. It contains only the pigment layer. The visual area, together with the reticular area, is bordered by the serrated line.
It is possible to examine the fundus and visualize the retina using ophthalmoscopy:
- Where the optic nerve exits, this place is called the optic disc. The location of the disc is 4 mm medial to the posterior pole of the organ of vision. Its dimensions do not exceed 2.5 mm.
- There are no photoreceptors in this place, so this zone has a special name - blind spot marriott... A little further there is a yellow spot, it looks like a retina having a diameter of 4-5 mm, it has a yellowish color and it consists of a large number of receptor cells. There is a fovea in the center, its size does not exceed 0.4-0.5 mm, it contains only cones.
- The central fossa is considered to be the place of the best vision; it passes through the entire axis of the organ of vision. The axis is a straight line that connects the central fossa and the fixation point of the organ of vision. Among the main structural elements, neurons are observed, as well as the pigment epithelium and vessels, together with neuroglia.
Retinal neurons are composed of the following elements:
- Visual analyzer receptors presented in the form of neurosensory cells, as well as rods and cones. The pigment layer of the retina maintains a relationship with photoreceptors.
- Bipolar cells - maintain synaptic communication with bipolar neurons. Such cells look like an insert link; they are in the path of signal propagation that travels along the retinal neural circuit.
- Synaptic connections with bipolar neurons represent ganglion cells. Together with the optic disc and axons, the optic nerve is formed. Thanks to this, the central nervous system receives important information. The three-membered neural chain consists of photoreceptor cells as well as bipolar and ganglion cells. They are connected by synapses.
- Horizontal cells are located near the photoreceptor and bipolar cells.
- The location of amacrine cells is considered to be the area of \u200b\u200blocation of bipolar, as well as ganglion cells. Horizontal and amacrine cells are responsible for modeling the process of transmission of the visual signal; the signal is transmitted along the three-membered retinal chain.
- The choroid includes the surface of the pigment epithelium, it forms a strong bond. The inner side of epithelial cells consists of processes, between which the location of the upper parts of the cones, as well as the rods, is visible. These processes have a poor relationship with the elements, therefore, sometimes there is a detachment of receptor cells from the main epithelium, in this case, retinal detachment occurs. The cells die and blindness sets in.
- The pigment epithelium is responsible for nutrition, as well as the absorption of light fluxes. The pigment layer is responsible for the accumulation and transmission of vitamin A, which is found in the composition of visual pigments.
There are capillaries in the human organs of vision - these are small vessels, over time they lose their original ability.
As a result of this, a yellow speck may appear near the pupil, where the sensation of color is located.
If the stain grows in size, the person will lose sight.
The eyeball receives blood through the main branch of the internal artery, it is called the ocular artery. Thanks to this branch, the organ of vision is nourished.
The network of capillary vessels provides nutrition for the eye. The major vessels help nourish the retina and optic nerve.
With age, the small vessels of the organ of vision - capillaries - wear out, the eyes begin to hold on to starvation rations, because there are not enough nutrients. At this level, blindness does not appear, the retina does not die, and the sensitive areas of the organ of vision undergo changes.
There is a yellow spot opposite the pupil. Its task is to provide maximum color resolution, as well as high chromaticity. With age, capillaries wear out, and the stain begins to change, grows old, so a person's eyesight deteriorates, he reads poorly.
The eyeball is covered with a special sclera... It represents the fibrous membrane of the eye along with the cornea.
The sclera looks like an opaque tissue, this is due to the chaotic distribution of collagen fibers.
The first function of the sclera is responsible for providing good vision. It acts as a protective barrier against the penetration of sunlight, if it were not for the sclera, the person went blind.
In addition, the shell does not allow external damage to penetrate; it serves as a real support for structures, as well as tissues of the organ of vision, which are located outside the eyeball.
These structures include the following bodies:
- oculomotor muscles;
- ligaments;
- vessels;
- nerves.
As a dense structure, the sclera maintains intraocular pressure and is involved in the outflow of intraocular fluid.
Scleral structure
In the outer dense shell, the area does not exceed 5/6 part, its thickness is different, in one place it is from 0.3-1.0 mm. In the area of \u200b\u200bthe equator of the eye organ, the thickness is 0.3-0.5 mm, the same dimensions are at the exit site of the optic nerve.
In this place, the formation of a lattice plate occurs, thanks to this, about 400 processes of ganglion cells come out, they are called differently - axons.
The structure of the iris includes 3 sheets, or 3 layers:
- front borderline;
- stromal;
- it is followed by the posterior pigment-muscle.
If you look closely at the iris, you can see the location of the various details.
At the highest place are the mesentery, thanks to which the iris is divided into 2 unequal parts:
- internal, it is smaller and pupillary;
- external, it is large and ciliary.
The brown border of the epithelium is located between the mesentery, as well as the pupillary edge. After that, the location of the sphincter is visible, then there are radial branching of the vessels. In the outer ciliary region there are outlined lacunae, as well as crypts that take place between the vessels, they look like spokes in a wheel.
These organs have a random nature, the clearer their location, the more uniformly the vessels are located. On the iris there are not only crypts, but also grooves that concentrate the limbus. These organs are able to affect the size of the pupil, due to which the pupil expands.
Ciliary body
The middle thickened part of the vascular tract includes the ciliary or otherwise, ciliary body... She is responsible for the production of intraocular fluid. The lens receives support thanks to the ciliary body, thanks to which the accommodation process takes place, this is called the thermal collector of the organ of vision.
The ciliary body is located under the sclera, in the very middle, where the iris and choroid are located, it is difficult to see it under normal conditions. On the sclera, the ciliary body is located in the form of rings, in which the width is 6-7 mm, it takes place around the cornea. The ring has a large width on the outside, and on the nasal side it is smaller.
The ciliary body has a complex structure:
Retina
In the visual analyzer there is a peripheral section called the inner lining of the eye or the retina.
The organ contains a large number of photoreceptor cells, thanks to this, perception easily occurs, as well as the transformation of radiation, where the visible part of the spectrum is located, this is converted into nerve impulses.
The anatomical mesh looks like a thin shell, which is located near the inner side of the vitreous, from the outside is located near the choroid of the organ of vision.
It consists of two different parts:
- Visual - it is the largest, it reaches the ciliary body.
- Front - it is called blind because there are no photosensitive cells in it. In this part, the main ciliary region is considered, as well as the iris region of the retina.
Refractive apparatus - how does it work?
The human organ of vision consists of a complex optical system of lenses, the image of the external world is perceived by the retina in an inverted and reduced form.
The dioptric apparatus includes several organs:
- transparent cornea;
- besides it, there are anterior and posterior chambers in which there is a watery wave;
- as well as the iris, it is located around the eye, as well as the lens and vitreous.
The radius of curvature of the cornea, as well as the location of the anterior and posterior surfaces of the lens, affects the refractive power of the organ of vision.
Chamber moisture
The processes of the ciliary body of the organ of vision produce a clear liquid - chamber moisture... It fills the parts of the eye, and is also located near the perivascular space. It contains elements that are in the cerebrospinal fluid.
Lens
The structure of this organ includes the nucleus along with the bark.
A transparent membrane is located around the lens; it has a thickness of 15 microns. An eyelash belt is attached near it.
The organ has a fixation apparatus; the main components are oriented fibers of various lengths.
They originate from the lens capsule, and then smoothly pass into the ciliary body.
Light rays pass through the surface, which is delimited by 2 media with different optical density, this is all accompanied by a special refraction.
For example, the passage of rays through the cornea is noticeable as they are refracted, this is due to the fact that the optical density of air differs from the structure of the cornea. After that, the light rays penetrate through the biconvex lens, it is called the lens.
When refraction ends, the rays occupy one place behind the lens and are in focus. Refraction is affected by the angle of incidence of light rays reflecting on the lens surface. The rays are more refracted from the angle of incidence.
More refraction is observed in rays that are scattered along the edges of the lens, in contrast to the central rays, which are perpendicular to the lens. They don't have the ability to refract. Because of this, a blurred spot appears on the retina, which has a negative effect on the organ of vision.
Thanks to good visual acuity, clear images on the retina appear due to the reflectivity of the optical system of the organ of vision.
Accommodation apparatus - how does it work?
When directing clear vision to a certain point in the distance, when tension returns, the organ of vision returns to the near point. Thus, the distance that is observed between these points is obtained and it is called the area of \u200b\u200baccommodation.
In people with normal vision, a high degree of accommodation is observed; this phenomenon is expressed in farsighted people.
When a person is in a dark room, a slight tension is expressed in the ciliary body, this is expressed due to a state of readiness.
Ciliary muscle
In the organ of vision there is an internal paired muscle, it is called ciliary muscle.
Thanks to her work, accommodation is carried out. It has another name, you can often hear how the ciliary muscle speaks to this muscle.
It consists of several smooth muscle fibers that differ in type.
The supply of blood to the ciliary muscle is carried out using 4 anterior ciliary arteries - these are branches of the arteries of the organ of vision. In front are the ciliary veins, they receive venous outflow.
Pupil
There is a round hole in the center of the iris of the human organ of vision, and it is called pupil.
It often changes in diameter and is responsible for regulating the flow of light rays that enter the eye and remain on the retina.
The constriction of the pupil occurs due to the fact that the sphincter begins to tighten. The expansion of the organ begins after the action of the dilator, it helps to influence the degree of illumination of the retina.
This work is done like the aperture of a camera, since the aperture is reduced in size after exposure to bright light, as well as strong lighting. Thanks to this, a clear image appears, blinding rays are as if cut off. The diaphragm expands if the light is dim.
This function is usually called diaphragm, it carries out its activities due to the pupillary reflex.
Receptor apparatus - how does it work?
The human eye has a visual retina, it represents the receptor apparatus. The inner lining of the eyeball, as well as the retina, includes the outer pigment layer, as well as the inner photosensitive nerve layer.
Retina and blind spot
Retinal development begins from the wall of the optic cup. It is the inner sheath of the organ of vision; it includes light-sensitive and pigmented sheets.
Its division was found for 5 weeks, at which time the retina is divided into two identical layers:
Yellow spot
In the retina of the organ of vision there is a special place where the greatest visual acuity is collected - this yellow spot... It is an oval and is located opposite the pupil, above it is the optic nerve. The yellow pigment is found in the cells of the spot, which is why it has that name.
The lower part of the organ is filled with blood capillaries. Thinning of the retina is noticeable in the middle of the spot, a fossa is formed there, which consists of photoreceptors.
Eye diseases
The human organs of vision repeatedly undergo various changes, because of this, a number of diseases develop that can change a person's vision.
Cataract
Clouding of the lens of the eye is called a cataract. The lens is located between the iris and the vitreous humor.
The lens has a transparent color, it is, in essence, a natural lens that is refracted by light rays and then transmitted to the retina.
If the transparency of the lens is lost, the light does not pass, vision becomes worse, and over time the person becomes blind.
Glaucoma
Refers to a progressive type of disease that affects the visual organ.
The retinal cells are gradually destroyed by the increased pressure that forms in the eye, as a result, the optic nerve atrophies, and visual signals do not enter the brain.
In a person, the ability of normal vision decreases, peripheral vision disappears, the field of vision decreases and becomes much smaller.
Myopia
A complete change in focus of vision is myopia, while a person has poor vision of far-away objects. The disease has another name - myopia, if a person is diagnosed with myopia, he sees objects located close.
Myopia is one of the common diseases associated with visual impairment. More than 1 billion people living on the planet suffer from myopia. One of the varieties of ametropia is myopia, these are pathological changes found in the refractive function of the eye.
Retinal detachment
Detachment of the retina belongs to severe and common diseases, in this case it is observed how the retina moves away from the choroid, it is called choroid. The retina of a healthy organ of vision is connected by the choroid, thanks to which it feeds.
A similar phenomenon is considered the most difficult among pathological changes; it does not lend itself to surgical correction.
Retinopathy
Due to the defeat of the retinal vessels, a disease appears retinopathy... It leads to the fact that the blood supply to the retina is disrupted.
It undergoes changes, as a result, the optic nerve atrophies, and then blindness sets in. During retinopathy, the patient does not feel pain symptoms, but a person sees floating spots in front of his eyes, as well as a veil, vision decreases.
Retinopathy can be diagnosed by a specialist diagnosis. The doctor will conduct a study of acuity, as well as visual fields, while ophthalmoscopy is used, biomicroscopy is done.
The fundus of the eye is checked for fluorescence angiography, electrophysiological studies must be done, in addition, an ultrasound of the organ of vision must be done.
Color blindness
The disease color blindness has its own name - color blindness. The peculiarity of vision is the violation of the distinction between several different colors or shades. Color blindness is characterized by symptoms that appear inherited or due to disorders.
Sometimes color blindness appears as a sign of a serious illness, it can be cataracts or brain diseases, or disorders of the central nervous system.
Keratitis
As a result of various injuries, or infections, as well as an allergic reaction, the cornea of \u200b\u200bthe organ of vision is inflamed and, as a result, a disease called keratitis is formed. The disease is accompanied by blurred vision, and then a strong decrease.
Strabismus
In some cases, there is a violation of the correct functioning of the eye muscles and, as a result, strabismus appears.
In this case, one eye deviates from the general point of fiction, the organs of vision are directed in different directions, one eye is directed to a specific object, and the other deviates from the normal level.
When squint occurs, binocular vision is impaired.
The disease is divided into 2 types:
- friendly,
- paralytic.
Astigmatism
In a disease, when focusing on any object, a partial or completely blurred image is expressed. The problem is that the cornea or lens of the organ of vision becomes irregular.
In astigmatism, a distortion of light rays is detected, there are several points on the retina, if the organ of vision is healthy, one point is located on the retina of the eye.
Conjunctivitis
Due to the inflammatory lesion of the conjunctiva, a manifestation of the disease is observed - conjunctivitis.
The mucous membrane that covers the eyelids and sclera undergoes changes:
- hyperemia forms on it,
- also puffiness,
- folds suffer along with the eyelids,
- purulent fluid is released from the eyes,
- there is a burning sensation
- tears begin to flow abundantly,
- there is a desire to scratch the eyes.
Loss of the eyeball
When the eyeball begins to protrude from the socket, appears proptosis... The disease is accompanied by puffiness of the eye membrane, the pupil begins to narrow, the surface of the organ of vision begins to dry out.
Lens dislocation
Among serious and dangerous diseases in ophthalmology, stands out dislocation of the lens.
The disease appears after birth or is formed after an injury.
One of the most important parts of the human organ of vision is the lens.
Thanks to this organ, light refraction is carried out, it is considered a biological lens.
The lens occupies a permanent place in the event that it is in a healthy state, a strong connection is observed in this place.
Eye burn
After the penetration of physical as well as chemical factors on the organ of vision, damage appears, which is called - eye burn... This can be due to low or high temperatures or exposure to radiation. Among chemical factors, chemical substances of increased concentration stand out.
Prevention of diseases of the organs of vision
Measures for the prevention and treatment of the organs of vision:
Vision - the pledge and wealth of the human organ of vision, so it must be protected from an early age.
Good vision depends on proper nutrition, and there should be foods containing lutein in the daily menu. This substance is found in the composition of green leaves, for example, it is found in cabbage, as well as in lettuce or spinach, it is also found in green beans.
Sleep physiology
Sleep is a peculiar state of the central nervous system, characterized by a shutdown of consciousness, inhibition of motor activity, a decrease in metabolic processes, and all types of sensitivity. During sleep, conditioned reflexes are inhibited and unconditioned ones are significantly weakened. Decreases heart rate, blood pressure, breathing becomes more rare and shallow. Sleep is a physiological requirement of the body. After sleep, the state of health, efficiency, attention improves. Sleep deprivation leads to memory impairments and can cause mental illness. There is a phase of slow sleep (slow high-amplitude waves predominate on the encephalogram) and a phase of REM sleep (frequent low-amplitude waves) - if a person is woken up in this phase, then he reports that he saw in a dream. In total, these 2 phases last about 1.5 hours, and then the cycle repeats again. An adult sleeps 1 time a day for 7-8 hours, such a dream is called single-phase sleep. In children, especially young children, sleep is multiphase, its duration is about 20 hours a day. In addition to normal, physiological sleep, there is also pathological sleep - when exposed to alcohol, drugs, hypnosis, etc. There are various theories to explain the mechanisms of sleep. According to one of them, sleep is a consequence of the body's self-poisoning (in particular, the brain) by metabolic products that accumulate during wakefulness (lactic acid, NH3, CO2, etc.). Another theory explains the alternation of sleep and wakefulness of the replaceable activity of the subcortical centers. During sleep, some centers are inhibited, while others are in a state of activity, processing the information received during the day, its redistribution and memorization.
Topic: "The organ of vision"
The organ of vision is located in the eye socket, the walls of which play a protective role. It is represented by the eyeball and auxiliary organs of the eye (eyebrows, eyelids, eyelashes, lacrimal apparatus). The eyeball in the section has an irregular spherical shape. It includes 3 shells, as well as transparent light-refracting media - the lens, vitreous body and aqueous humor of the eye chambers.
In the eyeball, there are 3 shells: outer - fibrous,
middle - vascular and internal - retina.
1. Outer - fibrous membrane is a dense connective tissue membrane that protects the eyeball from external influences, gives it shape and serves as a place of muscle attachment. It consists of 2 sections - a transparent cornea and an opaque sclera.
and) Cornea - the anterior part of the fibrous membrane, it looks like a transparent convex plate and serves to transmit light rays into the eye. The cornea does not contain blood vessels, but there are many nerve endings in it, so getting even a small speck on the cornea causes pain. Inflammation of the cornea is called keratitis.
b) Sclera - the posterior opaque part of the fibrous membrane, which has a white or bluish color. Vessels and nerves pass through it, the oculomotor muscles are attached to it.
2 . Middle (vascular) membrane - rich in blood vessels that feed the eyeball. It consists of 3 parts: the iris, the ciliary body and the choroid itself.
and) Iris - the anterior part of the choroid. It has the shape of a disc with a hole in the center - pupil, used to regulate the luminous flux. The iris contains pigment cells, the number of which determines the color of the eyes: with a large amount of melanin pigment, the eyes are brown or black, with a small amount of pigment - green, gray or blue. In addition, the iris contains smooth muscle cells, due to which the size of the pupil changes: with strong light, the pupil narrows, and with weak light, it expands. Inflammation of the iris - iritis.
b) Ciliary body - the middle thickened part of the choroid. It contains smooth muscle cells and supports the lens with the help of the ciliary girdle (zinn ligament). Depending on the contraction of the muscles of the ciliary body, these ligaments can stretch or relax, causing a change in the curvature of the lens. So, when examining close objects, the zinn ligament relaxes and the lens becomes more convex. When looking at distant objects, the ciliary band, on the contrary, is stretched and the lens is flattened. The ability of the eye to see objects at different distances (near and far) is called accommodation... In addition, the ciliary body filters transparent aqueous humor from the blood, which nourishes all the internal structures of the eye. Inflammation of the ciliary body - cyclitis.
in) Choroid itself - This is the back of the choroid. It lines the sclera from the inside and consists of a large number of vessels.
3. Inner shell -retina - adjacent to the choroid from the inside. It contains light-sensitive nerve cells - rods and cones. Cones perceive light rays in bright (daylight) light and at the same time are color receptors. They contain a visual pigment - iodopsin. The rods are twilight light receptors and contain the pigment rhodopsin (visual purple). The processes of rods and cones, joining in one bundle, form the optic nerve (II pair of cranial nerves). In the leaf of the optic nerve exit from the retina, light-sensitive cells are absent - this is the so-called blind spot. On the side of the blind spot, just opposite the lens, there is a macula - this is an area of \u200b\u200bthe retina in which only cones are concentrated, therefore it is considered the place of the greatest visual acuity. When rods and cones are irritated by light rays, the visual pigments they contain (rhodopsin and iodopsin) are destroyed. When the eyes are darkened, visual pigments are restored, and for this Vit A is needed. If Vit A is absent in the body, then the formation of visual pigment is impaired. This leads to the development of hemeralopia (night blindness), i.e. inability to see in low light or darkness.
1. In the eyeball, a fibrous membrane (tunica fibrosa bulbi) is isolated, which is the connective tissue layer of the eyeball. It serves as a support and protection for other membranes and parts of the eye. The back 2/3 of the fibrous membrane is called the tunica albuginea, or sclera, and the front 1/3 is called the cornea, or cornea. At the point of contact of these areas, there is a small scleral groove (sulcus sclerae).
The sclera (sclera) contains many elastic and collagen fibers and little basic connective tissue substance; they form a dense plate, in the outer layer of which there are no pigment cells. The tunica albuginea on the medial part of the posterior pole of the eye has a lattice structure. Processes of neurons that form the optic nerve penetrate through its holes. In the region of the posterior pole and equator of the eyeball, the thickness of the tunica albuginea is 0.3 - 0.4 mm, and near the cornea - 0.6 mm. In the tunica albuginea on its white background, arteries are sometimes clearly visible.
Veins are located mainly in the deep layers of the tunica albuginea and are not visible through the palpebral fissure. Especially well developed is the scleral venous sinus (sinus venosus sclerae), which is projected onto the surface of the eye along the sulcus sclerae. Resorption of fluid from the anterior chamber of the eye is carried out through the venous canal. From the inside, near the venous sinus, the iris joins the fibrous membrane, which forms the comb ligament (lig.pectinatum anguli iridocornealis). This ligament connects the outer edge of the iris to the sclera.
The cornea, or cornea (cornea), located at the anterior pole of the eye, is a transparent plate convex outwardly, which has five layers of epithelium and connective tissue fibers. The latter are enclosed in a colloidal substance of mucopolysaccharide nature. The cornea in the central part is slightly thinner (0.8 mm) than in the periphery (1.1 mm). It contains many sensitive nerve endings and is devoid of blood vessels; its nutrition is carried out by the diffusion of nutrients from the fluid of the anterior chamber of the eye and the vessels of the tunica albuginea adjacent to the edge of the cornea.
The structure of the cornea is peculiar, and this determines its transparency. Together with the liquid of the anterior chamber of the eyeball, it forms a biconvex lens having about 30D, which is the main refractive medium of the light beam.
2. The choroid (tunica vasculosa) is the middle layer of the eyeball. It contains a plexus of blood vessels and pigment cells. This shell is divided into three parts: the iris, the ciliary body, the choroid itself (Fig. 548).
548. Medial section of the eyeball.
1 - retina; 2 - visual artery and vein; 3 - choroid.
The iris, or iris, is 0.4 mm thick and refers to the anterior part of the choroid. It looks like a circular plate with a pupil (pupilla) in the center. The pupil width is variable, from 2 to 8 mm. The outer edge of the iris (margo ciliaris) is fused with the tunica albuginea and the ciliary body using the comb ligament; the inner edge (margo pupillaris) is almost even and limits the pupil. Depending on the intensity of illumination, the size of the pupil automatically changes, which is provided by the contraction of the radial (m. Dilatator pupillae) and circular (m. Sphincter pupillae) muscle fibers. The former are innervated by sympathetic fibers, the latter by parasympathetic. Elastic fibers, blood vessels, nerves and pigment cells take part in the formation of the iris along with the muscles; they determine the color of the iris. The iris is washed by fluid from the anterior and posterior chambers of the eye.
The ciliary body (corpus ciliare) is located on the inner surface at the junction of the sclera into the cornea. In cross section it has the shape of a triangle (Fig. 546), and when viewed from the side of the posterior pole - the shape of a circular ridge, on the inner surface of which there are about 70 radially oriented processes (processus ciliares). The ciliary body and iris are attached to the sclera by comb ligaments, having a spongy structure. These cavities are filled with fluid coming from the anterior chamber and then into the circular venous sinus (Schlemm's canal). Annular ligaments depart from the ciliary processes, which are woven into the lens capsule. The process of accommodation, that is, the adaptation of the eye to near or distant vision, is possible due to the weakening or tension of the annular ligaments; they are under the control of the muscles of the ciliary body, consisting of meridional and circular fibers (fibrae meridionales et circulares). With the contraction of the circular muscles, the ciliary processes approach the center of the ciliary circle and the annular ligaments weaken. Due to internal elasticity, the lens straightens and curvature increases; thereby reducing the focal length.
Simultaneously with the contraction of the circular muscle fibers, the meridional muscle fibers also contract, which tighten the posterior part of the choroid and the ciliary body as much as the focal length of the light beam decreases. When relaxing due to elasticity, the ciliary body takes its original position and, stretching the annular ligaments, strains the lens capsule, flattening it; the posterior pole of the eye also occupies its original position.
In old age, part of the muscle fibers of the ciliary body is replaced by connective tissue. The elasticity and firmness of the lens also decreases, resulting in impaired vision.
The choroid itself (chorioidea) occupies 2/3 of the back of the eyeball. The shell consists of elastic fibers, blood and lymph vessels, and pigment cells that create a dark brown background. It is loosely adhered to the inner surface of the tunica albuginea and is easily displaced during accommodation. In animals, calcium salts accumulate in this part of the choroid, which form an eye mirror that reflects light rays, which creates conditions for such eyes to glow in the dark.
3. The retina, or retina, the innermost one, extends to the serrated edge (area serrata), which lies at the junction of the ciliary body into the choroid itself. Along this line, the retina is divided into anterior and posterior parts.
The retina has 11 layers, which can be combined into two layers: pigment - outer and cerebral - inner. In the medulla are light-sensitive cells - rods and cones; their outer light-sensitive segments are directed towards the pigment layer, i.e. outward. The next layer is bipolar cells that form contacts with rods, cones, and ganglion cells, the axons of which form the optic nerve. In addition, there are horizontal cells located between rods and bipolar cells and amacrine cells to combine the function of ganglion cells (). The human retina contains about 125 million rods and about 6.5 million cones. The macula contains only cones, and the rods are located along the periphery of the retina. Retinal pigment cells isolate each light-sensitive cell from the other and from side rays, creating the conditions for imaginative vision.
In bright light, rods and cones are immersed in the pigment layer. In the corpse, the retina is dull white, without characteristic anatomical features. When viewed with an ophthalmoscope, the retina (fundus) in a living person has a bright red background due to translucence in the choroid of blood. Against this background, bright red blood vessels of the retina are visible (Fig. 549).
At the posterior pole of the eye, an oval spot is discernible - the disc of the optic nerve (discus n. Optici) 1.6-1.8 mm in size with a depression in the center (excavatio disci). Branches of the optic nerve, devoid of the myelin sheath, and veins converge radially to this spot; arteries diverge into the visual part of the retina. These vessels supply blood only to the retina (Fig. 549).
549. The fundus of the eyeball.
1 - artery; 2 - Vienna; 3 - yellow spot; 4 - the central fossa of the macula.
By the vascular pattern of the retina, one can judge the state of the blood vessels of the whole organism and some of its diseases. Laterally, 4 mm at the level of the optic nerve head, lies a macula with a central fossa (fovea centralis), painted red-yellow-brown. The focus of light rays is concentrated in the spot; it is the place of the best perception of light stimuli. The spot contains light-sensitive cells - cones, and rods are located along the periphery of the retina. Rods and cones lie on the periphery of the retina near the pigment layer. The light rays thus penetrate all layers of the transparent retina. Under the action of light, rhodopsin of rods and cones breaks down into retinene and protein (scotopsin). As a result of the decay, energy is generated, which is captured by the bipolar cells of the retina. Rhodopsin is constantly resynthesized from scotopsin and vitamin A.
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 white membrane, it is dense white, consists of connective tissue. This membrane 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, therefore, in acute diseases of the cornea, there is a strong lacrimation, photophobia. The cornea has no blood vessels, and the metabolism in it occurs due to the moisture of the anterior chamber and the 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 made up 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. With the contraction of these muscles, the ciliary body is pulled forward somewhat, which weakens the tension of the zinc 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. Eye color 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, made up of a network of blood vessels and muscles. The muscles of the iris are located radially and concentrically. When the 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. The retina is nourished through the vessels that enter the optic nerve, and then branch out and cover the entire surface of the retina. 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 nucleus-containing 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, nerve fiber layer and inner border membrane. (Kvinikhidze G.S. 1985). (see appendix 2)
The pigment epithelium is anatomically closely related to 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.
In the inner segment, the main cellular organelles are concentrated: an accumulation of mitochondria, polysomes, elements of the endoplasmic reticulum, and 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 to be 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. In the inner segment, the main cellular organelles are concentrated: an accumulation of mitochondria, polysomes, elements of the endoplasmic reticulum, and the Golgi complex. The cones in the inner segment have a section consisting of an accumulation of tightly adjacent mitochondria with a lipid drop located in the center of this accumulation - an ellipsoid. 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.