Let's get acquainted with the structure and functions of the sclera. Scleritis: how to recognize and treat eye pathology What is sclera
The opaque part of the fibrous membrane is the sclera of the eye. It covers 85% of all surfaces and is primarily responsible for transmitting visual information to the brain. Its structural features provide a wide range of functions. With anomalies and the development of pathologies, there is a risk of vision loss. Problems with the sclera cause a number of characteristic symptoms; if they exist, you should consult a doctor. Treatment depends on the current disease and the stage of its development; in most cases, local drug treatment is used.
Anatomy of the sclera
The sclera is the white membrane of the eye, located on the outside and, together with the cornea, is a fibrous tissue. Reaching the iris, it forms a dense protective ring. According to its physical characteristics, it has a white color and an opaque structure, due to which a person has vision. This is a fairly dense tissue of several layers; normally the thickness of the sclera reaches up to 1 mm. Despite this structure, the protein membrane of the eyeball can stretch, but this property decreases with age.
Shell structure
Density is ensured due to anatomical features. The structure of the sclera is a very complex process. The main component is collagen, it is arranged in a chaotic manner, thus causing the opacity of the eye. Full functionality is possible thanks to the multilayered shell, with the layers of the sclera differing in composition and density:
The shell has a very complex and intricate structure.
- Outer layer. The thinnest ball, filled with a large number of blood vessels.
- Middle layer. It is also called scleral and contains the maximum amount of collagen.
- Inner layer. It is a connective tissue in combination with the pigment part.
The visible part of the sclera is only the top layer, the subsequent ones are located inside, but when depleted, protrusion is possible. This process is observed in ophthalmic pathologies.
What functions does it perform?
The versatility of the shell is ensured by its complex structure. Each of the 3 layers plays its role and only a holistic effect guarantees full vision. All functions of the white membrane of the eye are quite diverse. First of all, we are talking about protecting the pupil from external damage. The sun has a negative effect on the condition of the eye. It is due to the refraction of light in the shell that the pupil does not dazzle and an image appears. In addition, the sclera performs the following functions:
The sclera makes it possible to move our eyes in the direction we need.
- Untangles with fastenings for the vascular and muscular apparatus.
- Provides blood outflow through venous branches.
- Responsible for eye mobility.
- Conducts moisture through the venous sinus of the sclera.
- Provides safe passage of the nerve to the eyeball.
What does healthy sclera look like?
You can distinguish a diseased state of the protein sphere from a healthy one by color. In infancy, the sclera is thin, so the membranes appear blue. This condition is not considered pathological and goes away on its own over time. What color of proteins in an adult may indicate the genetic nature of the problem; dystrophic changes have formed at the intrauterine level.
Yellowness of the sclera indicates possible pathologies. At the same time, the shell looks dull and cloudy. Such changes may indicate the impact of an infection. Lesions are not only local; kidney disease affects the color of the proteins. In old age, there may be large quantities of fat cells in the eyes; they can change color to yellow.
Diseases
The organ is susceptible to inflammatory processes caused by bacteria.
Pathologies that develop in the eyes at the level of the sclera are most often of an inflammatory nature, provoked by infections. However, primary sources are not always located directly in the organ. Painful manifestations in the membrane of the eye can only act as symptoms of the main processes. First of all, the ophthalmologist looks for the main diseases of the sclera, these include the following:
- Scleritis. An inflammatory pathology in which the inner layers of the membrane are affected.
- Staphyloma. The disease is caused by destructive processes, as a result of which the membrane is depleted.
- Episcleritis. Damage to the upper layer, accompanied by the formation of nodules.
Developmental anomalies
Congenital pathological forms pose a significant danger; they are difficult to diagnose and do not always respond to conservative treatment. These include blue sclera syndrome. This color may indicate insufficient iron in the blood. Often such a disease is not a single developmental deviation; other pathologies of the eyes, ears, and musculoskeletal system are also observed.
With an excess amount of melanin, the layers become yellow.Another congenital pathology is melanosis or melanopathy. This disease is also associated with pigmentation, only the membrane becomes yellow due to saturation with melanin. This process occurs as a result of a violation of carbohydrate metabolism. Changes in color may appear in different ways, with distinctive layers or spots appearing on the top layer.
A huge number of people have vision problems, some of which lead to complete loss of visual function. One such disease is scleritis.
What kind of disease is this?
Scleritis is an inflammatory process that occurs in the tissues of the sclera and deeply affects the episcleral vessels.
The disease can affect the choroid of the eyeballs and nearby episcleral tissues.
Complications of the disease include problems with vision, and in a severe stage - complete loss of vision. In many patients suffering from scleritis, it is chronic.
Children extremely rarely suffer from the appearance of scleritis. Mostly, parents do not recognize the disease immediately, mistaking it for other diseases that provoke eye inflammation. This leads to the disease moving into an advanced stage. It is very important to seek help from a doctor if you notice signs of inflammation in yourself or your child in order to diagnose and get rid of the problem.
ICD-10 code
H15.0 Scleritis
Causes
The appearance of scleritis can have various causes.
Previously, tuberculosis, sarcoidosis and syphilis were considered the most popular. Today, medicine, thanks to research, has revealed that the provocateurs of scleritis are streptococci, pneumococci, as well as inflammatory processes in the paranasal sinuses and any inflammatory processes in the body.
- In children, the disease appears during various infectious diseases that reduce the immune system and protective functions of the body.
- In older children, scleritis can also occur against the background of diabetes, rheumatism or tuberculosis.
Disruption of metabolic processes in the body also leads to the development of the disease.
The factor is very important. Inflammation often affects the sclera from the vascular system, and the development of purulent scleritis occurs endogenously.
Species
The eyeball includes anterior and posterior sections, so sclerite is also divided into anterior and posterior.
- The anterior one can appear in both an adult and a child;
- Posterior scleritis is diagnosed only in children.
Ultrasound of posterior scleritis
Based on how much the inflammatory process has spread in the eye shell, it can be:
Sometimes scleritis is purulent, and a swelling that has festered is visible in the eyes. It can only be removed surgically, revealing the suppuration.
In order not to take risks or endanger your vision, you must entrust such an operation only to a highly qualified ophthalmologist with experience in this field.
Symptoms
The symptoms of the disease directly depend on how extensive the inflammatory process is.
With nodular scleritis mild discomfort appears, and more serious types of the disease are accompanied by terrible pain, which can radiate to the temporal part, eyebrow, jaw and destroy scleral tissue. Depending on the inflammatory process, due to the fact that the blood vessels begin to dilate, limited or widespread redness may appear. The eyes may often water due to irritation of the nerve endings and resulting pain.
If light yellow spots appear on the sclera, the person may have necrosis, or the scleral tissue has begun to melt. Sometimes this is the only, but very dangerous manifestation of a disease that occurs without the characteristic symptoms of an inflammatory process.
When a person develops posterior scleritis , even a specialist cannot clearly diagnose it during a routine examination. However, there are symptoms that can help him during diagnosis:
- Swelling of the eyelids;
- Disorder in the functioning of nerve endings that are responsible for regulating eye functions;
- Swelling of the eye or its, provoked by an actively spreading inflammatory process.
Visual function weakens if there is swelling of the eye in the central area, its detachment, spread of infection deep into the eye membranes, or melting of the sclera.
Treatment
The specialist determines exactly how scleritis therapy will be carried out on an individual basis, having previously carried out all the necessary examinations and taking into account all the nuances of the disease.
The treatment takes a very long time, so you need to be patient and strictly follow the doctor’s instructions.
Taking any medications on your own is strictly prohibited. Any medications can be used to treat scleritis only as prescribed by the attending physician and strictly following the dosage so as not to put your health at risk.
Video:
It is possible to use traditional methods in the process of treating the disease, but only as eye hygiene and auxiliary therapy. It is strictly forbidden to use traditional medicine as the basis for all treatment.
Decoctions of the following herbs will help eliminate inflammatory processes and swelling of the eyes: chamomile, thyme, dill seeds, rose hips, soapwort and sage. It is very important to remember that you can also treat the affected area with herbal decoctions only with the permission of a doctor, so as not to further harm your health and vision.. If the sclera is thinned, then in some cases there is a need for a donor cornea transplant, which is done abroad.
A very controversial issue among doctors today is the benefits hirudotherapy in the treatment of scleritis. However, some specialists use such unconventional therapy in their practice, applying leeches to the temple area on the side of the diseased eye.
The sclera - the protein shell - is the outer dense connective tissue membrane of the eye, which performs protective and supporting functions. It is opaque because it consists of randomly arranged collagen fibers. Makes up 5/6 of the fibrous membrane of the eye.
The average thickness is from 0.3 to 1 mm, it is thinnest (0.3-0.5 mm) in the equator region and at the point where the optic nerve exits the eye. Here, the inner layers of the sclera form the lamina cribrosa, through which the axons of the retinal ganglion cells pass, forming the disc and stem part of the optic nerve.
Areas of thinning of the sclera are vulnerable to the effects of increased pressure (development of staphylomas, excavation of the optic nerve head) and damaging factors, primarily mechanical (subconjunctival tears in typical places, usually in areas between the attachment sites of extraocular muscles).
Near the cornea, the thickness of the sclera is 0.6-0.8 mm.
The sclera is poor in blood vessels, but its superficial, looser layer - the episclera - is rich in them.
The structure of the sclera
- Episclera is a superficial, looser layer, rich in blood vessels. In the episclera, superficial and deep vasculature are distinguished.
- The sclera's own substance contains predominantly collagen and a small amount of elastic fibers.
- The dark scleral plate is a layer of loose connective tissue between the sclera and the choroid itself, containing pigment cells.
In the posterior part, the sclera is represented by a thin lattice plate through which the optic nerve and retinal vessels pass. Two-thirds of the thickness of the sclera passes into the optic nerve sheath, and only one-third (inner) forms the lamina cribrosa. The plate is a weak point of the eye capsule and, under the influence of increased ophthalmotonus or impaired trophism, can stretch, putting pressure on the optic nerve and blood vessels, leading to disruption of the function and nutrition of the eye.
In the limbus region, three completely different structures merge - the cornea, sclera and conjunctiva of the eyeball. As a result, this zone can be the starting point for the development of polymorphic pathological processes - from inflammatory and allergic to tumor (papilloma, melanoma) and associated with developmental anomalies (dermoid).
The limbal zone is richly vascularized due to the anterior ciliary arteries (branches of the muscular arteries), which at a distance of 2-3 mm from it give off branches not only into the eye, but also in 3 other directions:
- directly to the limbus (forming the marginal vascular network)
- to the episclera
- to the adjacent conjunctiva
Along the circumference of the limbus there is a dense nerve plexus formed by long and short ciliary nerves. Branches extend from it, which then enter the cornea.
The scleral tissue has few vessels, it is almost devoid of sensitive nerve endings and is predisposed to the development of pathological processes characteristic of collegenesis.
6 extraocular muscles are attached to the surface of the sclera. In addition, it has special channels (graduates, emissaries). Along some of them, arteries and nerves pass to the choroid, and along others, venous trunks of various calibers exit.
On the inner surface of the anterior edge of the sclera there is a circular groove up to 0.75 mm wide. Its posterior edge protrudes anteriorly in the form of a spur, to which the ciliary body is attached (the anterior ring of attachment of the choroid). The anterior edge of the groove borders the Descimet's membrane of the cornea. At its bottom, at the posterior edge, there is the venous sinus of the sclera (Schlemm’s canal). The rest of the scleral recess is occupied by the trabecular meshwork (reticulum trabeculare).
Changes in the sclera with age
In a newborn, the sclera is relatively thin (0.4 mm), but more elastic than in adults; the pigmented inner membrane shines through it, and therefore the color of the sclera is bluish. With age, it thickens, becomes opaque and rigid. In older people, the sclera becomes even more rigid and, due to lipid deposition, acquires a yellowish tint.
Functions of the sclera
- The sclera is the attachment point for the eye muscles, which allow the eyeballs to move freely in different directions.
- Blood vessels penetrate through the sclera into the back of the eyeball - the short and long posterior ethmoidal arteries.
- 4-6 vortex (whirlpool) veins emerge from the eye in the equator region through the sclera, through which venous blood flows from the vascular tract.
- Sensory nerves from the ophthalmic nerve (the first branch of the trigeminal nerve) reach the eyeball through the sclera. Sympathetic innervation to the eyeball is directed from the superior cervical ganglion.
- Two-thirds of the thickness of the sclera passes into the optic nerve sheath.
The sclera is the outer layer of the eyeball, which covers 5/6 of its area. Due to the high density of the tissue, the sclera acts as a kind of opaque capsule with variable thickness.
The structure of the sclera
The structure of the sclera has three layers:
- The outer one, which is called the episclera;
- Middle, or sclera itself;
- Internal (brown plate).
The episclera contains a large number of blood vessels that provide blood with oxygen. In the upper regions, the blood flow is more powerful than in the remaining parts. This pattern is due to the fact that most of the vessels come from the muscle fibers of the anterior part of the eyeball.
The middle layer contains many collagen fibers and fibrocytes. The latter produce collagen as needed.
The brown plate contains a large amount of pigment, which gives a specific color to the tissues of this layer. Pigment cells that are found in the inner layer of the sclera are called zoromatophores. The endothelium is located on top of the brown plate.
The entire thickness of the sclera is penetrated by nerve fibers and vascular bundles that pass through special channels (emissaries).
Physiological sclera
The main role of the sclera is protective; it prevents the negative influence of external factors (mechanical and physical) on the internal structures of the eye. This ensures normal functioning of the eye and clear vision of objects. In addition, some muscle fibers are attached to the sclera, which help the eye move when studying the external world. This important function of the sclera is called support.
Video about the structure of the sclera of the eye
Symptoms of scleral damage
Scleral disease is characterized by the appearance of the following symptoms:
- Scleral rupture;
- Formation of dark spots on the surface;
- Decreased overall visual acuity;
- Changes in the structure of collagen fibers.
Diagnostic methods for scleral lesions
To identify pathology when scleral disease is suspected, perform the following manipulations:
- External visual inspection;
- eyes;
- eyes using a microscope.
Once again, it should be recalled that the main function of the sclera is protective, due to which it protects the eye from mechanical influence and negative environmental factors. In this regard, it is very important to care for this structure of the eye properly and undergo examinations by doctors to identify pathologies.
Diseases of the sclera
Due to the fact that the sclera protects the eye from external influences and provides a supporting function, disruption of its functioning negatively affects the entire optical system. Among scleral diseases, the following groups are distinguished:
- Congenital (in particular, melanosis);
- Acquired (for example, staphyloma,).
As the thickness decreases, the color of the sclera changes. Sometimes this is due to a disorder in the hearing aid. With melanosis, dark spots appear on the surface of the sclera.
When there is inflammation in the area of the eyeball, the process can affect other systems of the body, and therefore intervention is required.
From the first day a child is born, vision helps him understand the world around him. With the help of the eyes, a person sees a wonderful world of colors and sun, and visually perceives a colossal flow of information. Eyes give a person the opportunity to read and write, and get acquainted with works of art and literature. Any professional work requires us to have good, full vision.
A person is constantly exposed to a continuous stream of external stimuli and a variety of information about the processes inside the body. A person’s senses allow him to understand this information and correctly respond to a large number of events occurring around him. Among environmental stimuli, visual ones are especially important for humans. Most of our information about the outside world is related to vision. The visual analyzer (visual sensory system) is the most important of all analyzers, because it provides 90% of the information that goes to the brain from all receptors. With the help of our eyes, we not only perceive light and recognize the color of objects in the surrounding world, but also get an idea of the shape of objects, their distance, size, height, width, depth, in other words, about their spatial location. And all this is thanks to the subtle and complex structure of the eyes and their connections with the cerebral cortex.
The structure of the eye. Accessory apparatus of the eye
The eye is located in the orbital cavity of the skull - in the orbit, surrounded from behind and on the sides by the muscles that move it. It consists of the eyeball with the optic nerve and auxiliary devices.
The eye is the most mobile of all organs of the human body. He makes constant movements, even in a state of apparent rest. Fine eye movements (micromovements) play a significant role in visual perception. Without them it would be impossible to distinguish objects. In addition, the eyes make noticeable movements (macro movements) - turns, shifting the gaze from one object to another, tracking moving objects. Various movements of the eye, turning sideways, up, down, are provided by the extraocular muscles located in the orbit. There are six of them in total. Four rectus muscles are attached to the front of the sclera - and each of them turns the eye in its own direction. And two oblique muscles, superior and inferior, are attached to the back of the sclera. The coordinated action of the oculomotor muscles ensures the simultaneous rotation of the eyes in one direction or another.
The organ of vision needs protection from damage for normal development and function. The protective devices of the eyes are the eyebrows, eyelids and tear fluid.
The eyebrow is a paired arched fold of thick skin, covered with hair, into which the underlying muscles are woven. Eyebrows wick sweat away from the forehead and serve as protection from very bright light. The eyelids close reflexively. At the same time, they isolate the retina from light, and the cornea and sclera from any harmful effects. When blinking, tear fluid is evenly distributed over the entire surface of the eye, thereby preventing the eye from drying out. The upper eyelid is larger than the lower eyelid and is raised by a muscle. The eyelids close due to contraction of the orbicularis oculi muscle, which has a circular orientation of muscle fibers. Along the free edge of the eyelids there are eyelashes that protect the eyes from dust and too bright light.
Lacrimal apparatus. Tear fluid is produced by special glands. It contains 97.8% water, 1.4% organic matter and 0.8% salts. Tears moisturize the cornea and help maintain its transparency. In addition, they wash away foreign bodies, debris, dust, etc. from the surface of the eye, and sometimes the eyelids. The tear fluid contains substances that kill microbes through the lacrimal canaliculi, the openings of which are located in the inner corners of the eyes, enters the so-called lacrimal sac, and from here into the nasal cavity.
The eyeball has an irregular spherical shape. The diameter of the eyeball is approximately 2.5 cm. Six muscles are involved in the movement of the eyeball. Of these, four are straight and two are oblique. The muscles lie inside the orbit, start from its bony walls and are attached to the tunica albuginea of the eyeball behind the cornea. The walls of the eyeball are formed by three membranes.
Eye shells
On the outside it is covered with the tunica albuginea (sclera). It is the thickest, strongest and provides the eyeball with a certain shape. The sclera makes up approximately 5/6 of the outer shell, it is opaque, white and partly visible within the palpebral fissure. The tunica albuginea is a very strong connective tissue membrane that covers the entire eye and protects it from mechanical and chemical damage.
The front part of this shell is transparent. It's called the cornea. The cornea has impeccable cleanliness and transparency due to the fact that it is constantly rubbed by the blinking eyelid and washed with tears. The cornea is the only place in the protein membrane through which light rays penetrate into the eyeball. The sclera and cornea are rather dense formations that ensure the eye maintains its shape and protects its internal part from various external harmful influences. Behind the cornea there is a crystal clear liquid.
The second layer of the eye, the choroid, is adjacent to the sclera from the inside. It is abundantly supplied with blood vessels (performs a nutritional function) and pigment containing a coloring matter. The anterior part of the choroid is called the iris. The pigment in it determines the color of the eyes. The color of the iris depends on the amount of melanin pigment. When there is a lot of it, the eyes are dark or light brown, and when there is little, they are gray, greenish or blue. People who lack melanin are called albinos. In the center of the iris there is a small hole - the pupil, which, narrowing or expanding, lets in more or less light. The iris is separated from the choroid proper by the ciliary body. In its thickness there is the ciliary muscle, on the thin elastic threads of which the lens is suspended - a transparent body similar to a magnifying glass, a tiny biconvex lens with a diameter of 10 mm. It refracts light rays and brings them into focus on the retina. When the ciliary muscle contracts or relaxes, the lens changes its shape - the curvature of the surfaces. This property of the lens allows you to clearly see objects both at close and far distances.
The third, inner layer of the eye is the retina. The retina has a complex structure. It consists of light-sensitive cells - photoreceptors and perceives light entering the eye. It is located only on the back wall of the eye. There are ten layers of cells in the retina. Particularly important are the cells called cones and rods. In the retina, rods and cones are located unevenly. Rods (about 130 million) are responsible for the perception of light, and cones (about 7 million) are responsible for color perception.
Rods and cones have different purposes in the visual act. The first ones work on a minimum amount of light and constitute the twilight vision apparatus; Cones, on the other hand, operate in large amounts of light and serve for the daytime activities of the visual apparatus. The different functions of rods and cones make the eye highly sensitive to very high and low light levels. The ability of the eye to adapt to different brightness of light is called adaptation.
The human eye is capable of distinguishing an infinite variety of color shades. The perception of a variety of colors is provided by the cones of the retina. Cones are sensitive to colors only in bright light. In low light, color perception deteriorates sharply, and all objects appear gray in the twilight. Cones and rods work together. Nerve fibers depart from them, which then form the optic nerve, which leaves the eyeball and goes to the brain. The optic nerve consists of approximately 1 million fibers. Vessels pass through the central part of the optic nerve. At the exit site of the optic nerve, there are no rods and cones, as a result of which light is not perceived by this part of the retina.
Optic nerve (pathways)
The retina of the eye is the primary nerve center for processing visual information. The location where the optic nerve exits the retina is called the optic disc (blind spot). At the center of the disc, the central retinal artery enters the retina. The optic nerves pass into the cranial cavity through the optic nerve canals.
On the lower surface of the brain, a chiasma of the optic nerves is formed, but only the fibers coming from the medial parts of the retinas intersect. These intersecting visual pathways are called optic tracts. Most of the fibers of the optic tract rush into the lateral geniculate body of the brain. The lateral geniculate body has a layered structure and is so named because its layers bend like a knee. The neurons of this structure send their axons through the internal capsule, then as part of the visual radiation to the cells of the occipital lobe of the cerebral cortex near the calcarine sulcus. This path carries information only about visual stimuli.
Functions of vision
Systems | Appendages and parts of the eye | Functions |
Auxiliary | Brows | Removes sweat from the forehead |
Eyelids | Protects eyes from light rays, dust, drying out | |
Lacrimal apparatus | Tears moisten, cleanse, disinfect | |
Eyeball membranes | Protein |
|
Vascular | Nutrition of the eye | |
Retina | Light perception, light receptors | |
Optical | Cornea | Refracts light rays |
Aqueous moisture | Transmits rays of light | |
Iris (iris) | Contains pigment that gives color to the eye, regulates the opening of the pupil | |
Pupil | Adjusts the amount of light by expanding and contracting | |
Lens | Refracts and focuses light rays, has accommodation | |
Vitreous body | Fills the eyeball. transmits rays of light | |
Light-perceiving (visual receptor) | Photoreceptors (neurons) |
|
Optic nerve | Perceives the excitation of receptor cells and transmits it to the visual zone of the cerebral cortex, where the analysis of excitation and the formation of visual images occurs |
The eye as an optical device
In a parallel flow, light radiation hits the iris (acts as a diaphragm), with a hole through which light enters the eye; the elastic lens is a kind of biconvex lens that focuses the image; an elastic cavity (vitreous humor) that gives the eye a spherical shape and holds its elements in place. The lens and vitreous body have the properties of transmitting the structure of the visible image with the least distortion. Regulatory organs control involuntary movements of the eye and adapt its functional elements to specific conditions of perception. They change the throughput of the aperture, the focal length of the lens, the pressure inside the elastic cavity and other characteristics. These processes are controlled by centers in the midbrain with the help of many sensitive and executive elements distributed throughout the eyeball. The measurement of light signals occurs in the inner layer of the retina, which consists of many photoreceptors capable of converting light radiation into nerve impulses. Photoreceptors in the retina are distributed unevenly, forming three areas of perception.
The first - the viewing area - is located in the central part of the retina. It has the highest density of photoreceptors, so it provides a clear color image of the object. All photoreceptors in this area are basically the same in structure; they differ only in their selective sensitivity to the wavelengths of light radiation. Some of them are most sensitive to radiation (middle parts), others are in the upper part, and others are in the lower part. Humans have three types of photoreceptors that respond to blue, green and red colors. Here, in the retina, the output signals of these photoreceptors are jointly processed, as a result of which the contrast of the image is enhanced, the contours of objects are highlighted and their color is determined.
The volumetric image is reproduced in the cerebral cortex, where video signals from the right and left eyes are sent. A person's field of view covers only 5°, and only within its limits can he carry out visual and comparative measurements (orient himself in space, recognize objects, follow them, determine their relative location and direction of movement). The second area of perception performs the function of target acquisition. It is located around the viewing area and does not provide a clear image of the visible picture. Its task is to quickly detect contrasting targets and changes occurring in the external environment. Therefore, in this area of the retina the density of conventional photoreceptors is low (almost 100 times less than in the viewing area), but there are many (150 times more) other, adaptive photoreceptors that respond only to changes in the signal. Joint processing of signals from both photoreceptors ensures high performance of visual perception in this area. In addition, a person is able to quickly detect the slightest movements with peripheral vision. Grasping functions are controlled by parts of the midbrain. Here, the object of interest is not examined or recognized, but its relative location, speed and direction of movement are determined and a command is given to the oculomotor muscles to quickly rotate the optical axes of the eyes so that the object falls into the viewing area for detailed examination.
The third area is formed by the marginal areas of the retina, which do not receive the image of the object. The density of photoreceptors in it is the lowest - 4000 times less than in the viewing area. Its task is to measure the average brightness of light, which is used by vision as a reference point to determine the intensity of light streams entering the eye. This is why visual perception changes under different lighting conditions.
EYEBALL COVERS
I. Fibrous membrane, tunica fibrosa bulbi, covering the outside of the eyeball, it plays a protective role. In its larger posterior section it forms the tunica albuginea, or sclera, and in the anterior section it forms a transparent cornea. Both sections of the fibrous membrane are separated from each other by a shallow circular groove, sulcus sclerae.
1. Tunica albuginea, sclera, consists of dense connective tissue and is white in color. Its front part, visible between the eyelids, is known in everyday life as the white of the eye, hence the name of the shell. At the border with the cornea, in the thickness of the sclera, there passes a circular venous canal, sinus venosus sclerae (Schlemmi), - Schlemm's canal. Since light must penetrate to the light-sensitive elements of the retina lying inside the eyeball, the anterior section of the fibrous membrane becomes transparent and turns into the cornea (Fig. 368).
2. Cornea, cornea, which is a direct continuation of the sclera, is a transparent, round, convex anteriorly and concave posteriorly plate, which, like a watch glass, is inserted with its edge limbus corneae into the anterior section of the sclera.
The white membrane of the eye and its functions
The choroid of the eyeball, tunica vasculosa bulbi, rich in blood vessels, soft, dark-colored from the pigment it contains, lies immediately under the sclera. It has three sections: chorioidea, ciliary body and iris.
1. Chorioidea is the posterior, large section of the choroid. Due to the constant movement of the chorioidea during accommodation, a slit-like lymphatic space, spatium perichorioideale, is formed between both membranes.
2. Ciliary body, corpus ciliare, the anterior thickened part of the choroid, is located in the form of a circular ridge in the area of the transition of the sclera to the cornea. With its posterior edge, forming the so-called ciliary circle, orbicuius ciliaris, the ciliary body directly continues into the chorioidea. This place corresponds to the ora serrata of the retina (see below). Anteriorly, the ciliary body connects to the outer edge of the iris. The corpus ciliare in front of the ciliary circle bears about 70 thin, radially located whitish processes, processus ciliares (see Fig. 368, 369).
Due to the abundance and special structure of the vessels of the ciliary processes, they secrete liquid - the moisture of the chambers. This part of the ciliary body is compared with the plexus chorioideus of the brain and is considered as secessio (lat. - department). The other part - accommodative - is formed by smooth muscle, musculus ciliaris, which lies in the thickness of the ciliary body outward from the processus ciliares. Previously, this muscle was divided into 3 portions: external, meridional (Brucke), middle, radial (Ivanov) and internal, circular. In the latest literature, only two types of fibers are distinguished - meridional, fibrae meridionales, located longitudinally, and circular, fibrae circulares, located in a ring. The meridional fibers that form the main part of the ciliary muscle begin from the sclera and end posteriorly in the chorioidea. When they contract, they tighten the latter and relax the lens bag when placing the eye at close distances (accommodation). Circular fibers help accommodation by moving the anterior part of the ciliary processes, as a result of which they are especially developed in hypermetropes, who have to greatly strain the accommodation apparatus. Thanks to the elastic tendon, the muscle returns to its original position after contraction and an antagonist is not required.
Fibers of both types intertwine and form a single muscular-elastic system, which in childhood consists more of meridional fibers, and in old age - of circular ones. In this case, there is a gradual atrophy of muscle fibers and their replacement with connective tissue, which explains the weakening of accommodation in old age. In women, degeneration of the ciliary muscle begins 5-10 years earlier than in men, with the onset of menopause (Stieve).
3. Iris, or iris, iris, constitutes the most anterior part of the choroid and has the appearance of a circular, vertically standing plate with a round opening called the pupil, pupi11a. The pupil does not lie exactly in its middle, but is slightly shifted towards the nose. The iris plays the role of a diaphragm, regulating the amount of light entering the eye, due to which the pupil narrows in strong light and dilates in weak light. With its outer edge, margoсiliaris, the iris is connected to the ciliary body and sclera, while its inner edge, surrounding the pupil, margo pupillaris, is free. The iris is divided into the anterior surface, facies anterior, facing the cornea, and the posterior, facies posterior, adjacent to the lens. The anterior surface, visible through the clear cornea, has different colors among different people and determines the color of their eyes. This depends on the amount of pigment in the surface layers of the iris. If there is a lot of pigment, then the eyes are brown (brown) up to black; on the contrary, if the pigment layer is poorly developed or even almost absent, then mixed greenish-gray and blue tones are obtained. The latter mainly arise from the translucency of the black retinal pigment on the back of the iris. The iris, performing the function of a diaphragm, has amazing mobility, which is ensured by the fine adaptability and correlation of its components.
Intraocular tumors
Thus, the base of the iris, stroma iridis, consists of connective tissue having a lattice architecture into which vessels are inserted, running radially from the periphery to the pupil. These vessels, which are the only carriers of elastic elements since the connective tissue of the stroma does not contain elastic fibers), together with the connective tissue form the elastic skeleton of the iris, allowing it to easily change in size.
The movements of the iris themselves are carried out by the muscular system located in the thickness of the stroma. This system consists of smooth muscle fibers, which are partly located in a ring around the pupil, forming the muscle that constricts the pupil, m. sphincter pupillae, and partly diverge radially from the pupillary opening and form the muscle that dilates the pupil, m. dilatator pupillae. Both muscles are interconnected and act on each other: the sphincter stretches the dilator, and the dilator straightens the sphincter. Thanks to this, each muscle falls into its original position, which achieves the speed of movements of the iris. This single muscular system has a punctum fixum on the ciliary body.
M. sphincter pupillae is innervated by parasympathetic fibers coming from the Yakubovich nucleus as part of n. oculomotorius, a m. dilatator pupillae- sympathetic from tr. sympathicus.
The impermeability of the diaphragm to light is achieved by the presence of a double-layer pigment epithelium on its posterior surface. On the anterior surface, washed by fluid, it is covered with the endothelium of the anterior chamber.
The median location of the choroid between the fibrous and retina helps its pigment layer to retain excess rays falling on the retina and distribute blood vessels in all layers of the eyeball.
Vessels and nerves of the choroid. Arteries originate from branches of a. ophthalmica, of which some enter from behind the eyeball (aa. ciliares posteriores breves et longi), and others from the front along the edge of the cornea (aa. ciliares anteriores). Anastomosing with each other around the ciliary edge of the iris, they form circulus arteriosus iridis major, from which branches extend to the corpus ciliare and the iris, and around the pupillary opening - circulus arteriosus iridis minor. Veins form a dense network in the choroid. Blood is removed from them mainly through 4 (or 5-6) vv. vorticosae (resembling a whirlpool, vortex), which along the equator of the eyeball at equal distances pierce the tunica albuginea obliquely and flow into the orbital veins. In front, the veins from the ciliary muscle flow into the sinus venosus sclerae (Schlemm's canal), which has an outflow into the vv. ciliares anteriores. Schlemm's canal also communicates with the lymphatic bed through a system of fissures in the fountain space.
The nerves of the choroid contain sensory (from n. trigeminus), parasympathetic (from n. oculomotorius) and sympathetic fibers.
III. Retina, or retina, retina(Fig. 370), the innermost of the three membranes of the eyeball, adjacent to the choroid along its entire length up to the pupil.
In contrast to the other membranes, it comes from the ectoderm (from the walls of the optic cup; see “Development of the eye”) and, according to its origin, consists of two layers, or sheets: the outer one, containing pigment, stratum pigmenti retinae, and the inner one, which represents the retina, retina , in the proper sense. The retina, in its own sense, is divided according to its function and structure into two sections, of which the posterior one contains light-sensitive elements - pars optica retinae, and the anterior one does not contain them. The boundary between them is marked by a jagged line, ora serrata, passing at the level of the transition of the chorioidea into the orbiculus ciliaris of the ciliary body. Pars optica retinae is almost completely transparent and only becomes cloudy on the corpse.
When viewed in a living person through an ophthalmoscope, the fundus of the eye appears dark red due to the transmission of blood in the choroid through the transparent retina. Against this red background, at the bottom of the eye, a whitish round spot is visible, representing the place where the optic nerve exits the retina, which, leaving it, forms the so-called optic disc, discus n. optici, with a crater-shaped depression in the center (excavato disci).
When examined with a mirror, the vessels of the retina emanating from this recess are also clearly visible. The optic nerve fibers, having lost their myelin sheath, spread from the disc in all directions along the pars optica retinae. The optic disc, about 1.7 mm in diameter, lies slightly medial (towards the nose) from the posterior pole of the eye. Laterally from it and at the same time slightly to the temporal side from the posterior pole, noticeable in the form of an oval field 1 mm in diameter is the so-called spot, macula, colored in a living red-brown color with a pinpoint fovea, fovea centralis, in the middle. This is the place of greatest visual acuity (Fig. 371).
The retina contains light-sensitive visual cells, the peripheral ends of which are shaped like rods and cones. Since they are located in the outer layer of the retina, adjacent to the pigment layer, light rays must pass through the entire thickness of the retina to reach them. The rods contain the so-called visual purple, which gives a pink color to the fresh retina in the dark, but it becomes discolored in the light. The formation of purple is attributed to the cells of the pigment layer. Cones do not contain visual purple. It should be noted that the macula contains only cones and no rods. In the area of the optic nerve there are no light-sensitive elements at all, as a result of which this place does not provide visual sensation and is therefore called a blind spot.
Retina vessels. The retina has its own system of blood vessels. It is supplied with arterial blood from a special branch from a. ophthalmica - central retinal artery, a. centralis retinae, which penetrates the thickness of the optic nerve even before it leaves the eye, and then is directed along the axis of the nerve to the center of its disk, where it is divided into superior and inferior branches. Branches a. centralis retinae extend to ora serrata. Veins fully correspond to arteries and are called like them by the same names with the substitution of only the word venula. All venous branches of the retina are collected in v. centralis retinae, which goes along with the artery of the same name along the axis of the optic nerve and flows into v. ophthalmica superior or directly into the sinus cavernosus.
The word sclera
The word sclera in English letters (translit) - sklera
The word sclera consists of 6 letters: a e k l r s
Meanings of the word sclera. What is sclera?
Sclera (from the Greek σχληρός - hard) - the protein shell - the outer dense connective tissue membrane of the eye, which performs protective and supporting functions. Formed by collagen fibers collected in bundles. Makes up 5/6 of the fibrous membrane of the eye.
en.wikipedia.org
Sclera (from the Greek skleros - hard), tunica albuginea, tunica albuginea, outer dense connective tissue membrane of the eye, performing supporting and protective functions.
TSB. - 1969-1978
SCLERA SCLERA (from the Greek scleros - hard), the outer dense connective tissue opaque membrane covering the back of the eyeball of vertebrates, and in front (in front of the pupil) turning into a transparent cornea...
Biological encyclopedic dictionary. — 1986
The sclera or tunica albuginea (Sclera) is the outermost membrane of the eyeball and surrounds approximately 4/5-5/6 of it, in which in front it directly passes into the cornea, and in the back it is pierced by the optic nerve (see Eye).
Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron. — 1890-1907
SCLERA (EYE BALL), PROTEIN TUNER OF THE EYE
Sclera, Sclerotic Coat Sclera, Sclerotic Coat - the white outer fibrous coat of the eyeball.
Medical terms from A to Z
SCLERA (EYE BALL), EYE COAT PROTEIN (sclerotic coat) - the white outer fibrous coat of the eyeball. At the front of the eye, this layer becomes the cornea. See Eye. - Scleral.
Sclera (Eyeball) (Sclera), Cover of the Eye Albuginea (Sclerotic Coat) is the white outer fibrous membrane of the eyeball. At the front of the eye, this layer becomes the cornea. See Eye. - Scleral.
Medical terms. — 2000
Russian language
Sclera.
Morphemic-spelling dictionary. - 2002
(sclero-; Greek skleros hard, dense) a component of compound words, meaning: 1) “hard”, “compacted”; 2) “relating to the sclera.”
Large medical dictionary. — 2000
(Sclero-; Greek sklēros hard, dense) a component of compound words, meaning: 1) “hard”, “compacted”; 2) “relating to the sclera.”
Medical ecyclopedia
Sclero- (Scler-), Sclero (Sclero-)
SCLER- (SCLER-), SCLERO (sclero-) is a prefix meaning: 1. Compaction or thickening of something. 2. Sclera. 3. Sclerosis.
Scler- (Scler-), Sclero (Sclero-) is a prefix meaning: 1. Compaction or thickening of something. 2. Sclera. 3. Sclerosis.