Optical properties of the refractive media of the eye. Optical system of the eye

home

Kinds

The eye is the organ of vision (Fig. 1), a very complex sensory organ that perceives the action of light. The human eye is irritated by rays of a certain part of the spectrum. It is affected by electromagnetic waves with a length of approximately 400 to 800 nm, which, when afferent impulses enter the visual analyzer of the brain, causes visual sensations. The functions of the eye are very diverse. Through the eye, the shape of objects, their size, distance from the eye, the direction in which they move, their immobility, the degree of illumination, color, and color are determined.

Since the most important part of the eye - the retina with the optic nerve - develops directly from brain tissue, the eye is a part of the brain extended to the periphery.

Refractive media.

The eye consists of two systems:

1) optical system of light-refracting media and
2) the retinal receptor system.

The light-refracting media of the eye include: the cornea, the aqueous humor of the anterior chamber of the eye, the lens and the vitreous body. Each of these media has its own refractive index. Corneal refractive index - 1.37; aqueous humor and vitreous humor - 1.33; outer layer of the lens - 1.38; lens nuclei - 1.40. clear vision exists only if the refractive media of the eye are transparent.

The shorter the focal length, the greater the refractive power of the optical system, which is expressed in diopters. Diopter is the refractive power of a lens with a focal length of 1 m. The refractive power of the optical system of the eye is equal (in diopters): cornea - 43; lens when looking into the distance - 19; at the maximum approach of the object to the eye - 33. the refractive power of the entire optical system of the eye is equal for distance - 58; and at the maximum approach of the object - 70.

Refractive media of the eyeball: cornea, fluid of the eye chambers, lens, vitreous body.

The inner nucleus of the eye consists of transparent light-refracting media: the vitreous body, the lens, and the aqueous humor of the chambers of the eye.

The vitreous body is located in the vitreous chamber. Its volume for an adult is 4 ml. In composition, it is a gel-like medium with the presence of special proteins in the framework: vitrosin and mucin, with which hyaluronic acid is associated, which ensures the viscosity and elasticity of the body. The primary vitreous develops from the mesoderm, the secondary - from the mesoderm and ectoderm. The formed vitreous body is a permanent environment of the eye, which is not restored if lost. It is covered along the perimeter with a limiting membrane, which is firmly connected with the ciliary epithelium (the base is a ring-shaped base protruding anterior to the serrated edge) and with the posterior part of the lens capsule (hyaloid-lens ligament).

The lens is located between the iris and the vitreous body, in a recess (vitreous fossa) and is held in place by the fibers of the ciliary girdle.

In the lens there are different types:

the anterior surface of the capsule (epithelium and fibers) with the most protruding point - the pole;
posterior surface of the capsule (epithelium and fibers) with a more convex posterior pole;
equator - transition of the front surface to the back;
lens substance made of lens fibers and the formation that glues them together; lens nucleus - lens fibers without nuclei: sclerotic, compacted;
ciliary girdle, the fibers of which begin from the anterior and posterior surfaces of the capsule in the equator region.

The axis of the lens is the distance between the poles, the refractive power of the lens is 18 diopters (D).

The anterior chamber is located between the cornea and the iris, between the iris and the anterior surface of the lens capsule - rear camera. Both are filled with moisture, capable of slight refraction of light.

The anterior chamber is bounded along the perimeter by the pectineal ligament, between the bundles of fibers of which there are spaces of the iris-corneal angle lined with flat cells (fountain spaces) - the path for the outflow of moisture into the venous sinus of the sclera. Damage to the angle underlies the development of angular glaucoma.

The posterior chamber exchanges moisture due to the slit-like spaces between the fibers of the ciliary girdle, which, in the form of a common circular slit (Petite canal), cover the lens along the periphery.

The cornea is located in the outer shell of the eye, making up its anterior part and participating with its convexity in the formation of the anterior pole of the eyeball. It is transparent, has a round shape with a diameter of 12 mm in an adult, and a thickness of 1 mm. In the sagittal plane it is smoothly curved. On the outer surface the cornea is convex, and on the inner surface it is concave. The radius of curvature is up to 7.5-8 mm, which ensures light refraction of up to 40 diopters. The cornea grows into the circular groove of the sclera, forming with its peripheral edge a small thickening - the limbus.

There are five layers in the cornea:

anterior epithelium up to 50 µm thick with numerous free nerve endings; characterized by high regeneration and permeability to drugs;
anterior border plate 6-9 µm thick;
its own substance from fibrous plates, including bundles of collagen fibers, branched flat fibroblasts and an amorphous medium of keratin sulfates, glycosaminoglycans and water;
posterior border plate 5-10 µm thick; both plates: anterior and posterior consist of collagen fibers and amorphous substance;
posterior epithelium of flat polygonal cells of various shapes.

The cornea has no vessels; it receives diffuse nutrition from the fluid of the anterior chamber and the vessels of the circular groove of the sclera.

Visual analyzer. Represented by the perceptive department - receptors of the retina, optic nerves, conduction system and corresponding areas of the cortex in the occipital lobes of the brain.

Light refractive apparatus of the eye.

Includes the cornea, lens, vitreous body, fluid of the anterior and posterior chambers of the eye.

Cornea consists of collagen fibrils having a parallel orientation. Microscopically, 5 layers are distinguished: 1. Anterior stratified squamous non-keratinizing epithelium 2. Anterior limiting membrane (Bowman's membrane) 3. Corneal substance 4. 3 posterior limiting membrane (Descemet's membrane) 5. Posterior epithelium. The anterior epithelium is multilayered squamous, non-keratinizing, covered with lacrimal fluid, and contains many receptor endings. The posterior epithelium is single-layer squamous.

Lens. It is based on lens fibers (each fiber is a transparent hexagonal prism), which are derivatives of epithelial cells without nuclei. The cytoplasm of the lens fibers contains a transparent protein, crystallin. The central fibers are shortened and overlap each other, forming the nucleus of the lens. The outside of the lens is covered with a transparent capsule (similar to a thickened basement membrane). Cambial cells are located on the posterior surface of the lens. The lens is fixed using the fibers of the ciliary girdle, which are attached to the ciliary body on one side and to the lens capsule on the other.

Vitreous body- transparent jelly-like mass. Fills the cavity between the lens and the retina. Contains protein vitrein and hyaluronic acid.

Aqueous moisture fills the anterior and posterior chambers of the eye. The composition of moisture is close to blood plasma, but it is separated from the blood by a barrier that prevents the penetration of leukocytes into it.

Photoreception mechanism associated with the disintegration of rhodopsin and iodopsin molecules under the influence of light energy. This triggers a chain of biochemical reactions, which are accompanied by a change in membrane permeability in rods and cones and the appearance of an action potential. After the breakdown of the visual pigment, its resynthesis follows, which occurs in the dark and in the presence of vitamin A. A lack of vitamin A in food can lead to impaired twilight vision ( night blindness). Color blindness (color blindness) is explained by the genetically determined absence of one or more types of cones in the retina. The excitation of the neurosensory cell is transmitted through the central process to the 2nd bipolar neuron. The cell bodies of bipolar neurons lie in the inner nuclear layer of the retina. In this layer, in addition to bipolar neurons, there are two more types of associative neurons: horizontal and amacrine. Bipolar neurons connect rod and cone optic cells to neurons in the ganglion layer. In this case, cone cells contact bipolar neurons in a 1:1 ratio, while several rod cells form connections with one bipolar cell. Horizontal nerve cells have many dendrites, with the help of which they contact the central processes of photoreceptor cells. The horizontal cell axon also makes contact with synaptic structures between the receptor and bipolar cells. Multiple synapses of a peculiar type arise here. The transmission of impulses through such a synapse and further with the help of horizontal cells can cause the effect of lateral inhibition, which increases the contrast of the image of the object. A similar role is played by amacrine neurons located at the level of the inner reticular layer. Amacrine neurons do not have an axon, but have branched dendrites. The neuron body plays the role of a synaptic surface.

Refractive errors: myopia, farsightedness, astigmatism. Causes of disturbances in light perception. Visual acuity. Binocular vision. Spatial vision. Adaptation of the visual analyzer.

Myopia or myopia is the most common type of refractive error. With myopia, objects can be seen more or less clearly only at a close distance, which is why the very concept of “myopia” arose. With myopia, the image of objects in the eye is formed in front of the retina. At the same time, in people suffering from myopia (myopia), the length of the eye is increased (axial myopia), or the cornea has a greater refractive power, which is why a change occurs focal length(refractive myopia). Usually these two points are combined. Myopia (or myopia) appears due to excessive growth of the eyeball and the strong refractive power of the optical apparatus, which is manifested by decreased distance vision.

At the moment, there is no single substantiated scientific concept of the development of myopia. It is assumed that different types myopias have different origins, and their development is due to one of the factors or has a complex genesis.

Various factors can contribute to the occurrence and development of myopia (myopia):

- strong visual load, bad light workplace, as well as incorrect sitting position when reading and writing, reading while lying down;

- hereditary predisposition;

- congenital weakness of connective tissue;

- poor nutrition, various diseases, overwork - i.e. general weakening of the body;

- primary weakness of accommodation, leading to compensatory stretching of the eyeball;

- unbalanced tension of accommodation and convergence, causing a spasm of accommodation and the development of false and then true myopia.

Farsightedness is a visual impairment in which a person sees poorly up close and quite well at a distance. However, when high degree farsightedness, the patient may have difficulty seeing distant objects.

Farsightedness usually occurs due to the fact that the eyeball has an irregular shape, as if it is compressed along the longitudinal axis. As a result, the image of the object is focused not on the retina, but behind it. Often the irregular, compressed shape of the eyeball is combined with insufficient optical power of the cornea and lens. Much less often, farsightedness is caused only by the weakness of the optical system of the eye with a normal length of the eyeball.

Symptoms of farsightedness.

As mentioned above, the main sign of farsightedness is poor near vision with satisfactory or even excellent distance vision. However, with a high degree of farsightedness, the patient may have difficulty seeing distant objects. Besides,

Constant companions of farsightedness are increased eye fatigue, eye strain when reading and writing, headaches, burning eyes. Farsightedness is often accompanied by inflammatory eye diseases (blepharitis, barley, conjunctivitis), and in children - strabismus and lazy eye syndrome (amblyopia).

Astigmatism is characterized by the fact that the cornea has an irregular shape, as a result of which the refractive power of the cornea is not the same in different meridians. This causes light rays entering the eye to be focused at two points instead of one. Astigmatism often accompanies myopia (myopic astigmatism) or farsightedness (far-sighted astigmatism) or a combination of both (mixed astigmatism).

Typically, astigmatism results in a person's vision being "blurry." Frequent companions of astigmatism are headaches and increased eye fatigue. Note that with low-grade astigmatism, patients may not experience any discomfort, therefore, for timely diagnosis of this, and many other eye diseases, it is necessary to undergo regular preventive examinations by an ophthalmologist.

Binocular vision - the ability to clearly see the image of an object with both eyes at the same time; in this case, a person sees one image of the object he is looking at, that is, this is vision with two eyes, with a subconscious connection in the visual analyzer (cerebral cortex) of the images received by each eye into a single image. Creates three-dimensionality of the image. Binocular vision is also called stereoscopic.

If binocular vision does not develop, it is possible to see only in the right or left eye. This type of vision is called monocular.

Alternating vision is possible: either with the right or with the left eye - monocular alternating. Sometimes vision occurs with two eyes, but without merging into one visual image - simultaneous.

The absence of binocular vision with two eyes open externally manifests itself in the form of gradually developing strabismus.

Determination of visual acuity - a numerical expression of the eye’s ability to perceive separately two points located at a certain distance from each other.

Eye adaptation - adaptation of the eye to changing lighting conditions. The changes in the sensitivity of the human eye during the transition from bright light to complete darkness (the so-called dark adaptation) and during the transition from darkness to light (light adaptation) have been most fully studied. If an eye that was previously exposed to bright light is placed in the dark, its sensitivity increases at first quickly, and then more slowly.

Visual analyzer. Light refractive apparatus of the eye, its properties. Mechanisms of photoreception

Knowledge of these indicators, as well as some additional information, made it possible to calculate the total refractive power of the diopter of the eye using special formulas. It is equal to 58.6 diopters for the eye.

Refractive power is measured by the equation 1/f, where f is the focal length.

If it is given in meters, the unit of refractive (optical) power will be diopter. The focal length itself

Rice. 9. Constructing an image.

AB – subject; ab - his image; 0 is the nodal point.

behind the lens depends on the difference in refractive indices at the boundary of two interfaces and on the radius of curvature of the interface between these media.

The main refractive media are the cornea and lens. The lens is enclosed in a capsule, which is attached by cyanogen ligaments to the ciliary body. Due to the contraction of the ciliary muscles, the curvature of the lens changes. 4

10 Lens and ciliary band.

1 - lens substance. Consists of a nucleus and cortex, 2 - lens cortex; 3 - lens nucleus, 4 - lens epithelium: 5 - posterior surface of the lens, 6 - lens fibers; 7 - lens capsule. A transparent membrane up to 15 microns thick that surrounds the lens. Serves as the attachment point for the ciliary girdle; 8 - ciliary belt. The fixing apparatus of the lens, consisting of radially oriented fibers of various lengths: 9 - girdle fibers They start from the lens capsule and pass into the ciliary body.

The passage of light rays through a surface separating two media with different optical densities is accompanied by refraction of the rays (refraction). For example, when rays pass through the cornea, their refraction is observed, because The optical density of air and the cornea is very different. Next, the rays from the light source pass through a biconvex lens - the lens.

As a result of refraction, the rays converge at a certain point behind the lens - at the focus. Refraction depends on the angle of incidence of light rays on the surface of the lens: The greater the angle of incidence, the more strongly the rays are refracted. The rays incident on the edges of the lens are refracted more than the central rays passing through the center perpendicular to the lens, which are not refracted at all. This leads to the appearance of a blurred spot on the retina, which reduces visual acuity.

Visual acuity reflects the ability of the eye's optical system to produce clear images on the retina.

Light refractive apparatus of the eye

The refractive (dioptric) apparatus of the eye includes the cornea, lens, vitreous body, fluids of the anterior and posterior chambers of the eye.

Cornea (cornea) occupies 1/16 of the area of the fibrous membrane of the eye and, performing a protective function, is characterized by high optical homogeneity, transmits and refracts light rays and is integral part light refractive apparatus of the eye.

The plates of collagen fibrils that make up the main part of the cornea have correct location, the same refractive index with the nerve branches and interstitial substance, which, together with chemical composition determines its transparency.

The thickness of the cornea is 0.8-0.9 microns in the center and 1.1 microns at the periphery, the radius of curvature is 7.8 microns, the refractive index is 1.37, the refractive power is 40 diopters.

Microscopically, 5 layers are distinguished in the cornea: 1) anterior multilayered squamous non-keratinizing epithelium; 2) anterior limiting membrane (Bowman's membrane); 3) own substance of the cornea; 4) posterior limiting elastic membrane (Descemet's membrane); 5) posterior epithelium (“endothelium”).

The cells of the anterior epithelium of the cornea are tightly adjacent to each other, arranged in 5 layers, connected by desmosomes.

The basal layer is located on Bowman's membrane. Under pathological conditions (if the connection between the basal layer and Bowman's membrane is not strong enough), detachment from the basal layer of Bowman's membrane occurs.

The cells of the basal layer of the epithelium (germinative, germinal layer) have a prismatic shape and an oval nucleus located close to the top of the cell. Adjacent to the basal layer are 2-3 layers of polyhedral cells. Their laterally elongated processes are embedded between neighboring epithelial cells, like wings (winged, or spiny, cells).

The nuclei of winged cells are round. The two superficial epithelial layers consist of sharply flattened cells and have no signs of keratinization. The elongated narrow nuclei of the cells of the outer layers of the epithelium are located parallel to the surface of the cornea. The epithelium contains numerous free nerve endings, which determine the high tactile sensitivity of the cornea.

The surface of the cornea is moistened with the secretion of the lacrimal and conjunctival glands, which protects the eye from the harmful physical and chemical effects of the outside world and bacteria. The corneal epithelium has a high regenerative capacity. Under the corneal epithelium there is a structureless anterior limiting membrane ( lamina limitans interna) - Bowman's shell with a thickness of 6-9 microns.

It is a modified hyalinized part of the stroma, is difficult to distinguish from the latter and has the same composition as the cornea's own substance. The boundary between Bowman's membrane and the epithelium is well defined, and the fusion of Bowman's membrane with the stroma occurs imperceptibly.

Proper substance of the cornea ( substantia propria cornea) - stroma - consists of homogeneous thin connective tissue plates, intersecting at an angle, but regularly alternating and located parallel to the surface of the cornea.

Processed flat cells, which are types of fibroblasts, are located in the plates and between them. The plates consist of parallel bundles of collagen fibrils with a diameter of 0.3-0.6 microns (1000 in each plate). Cells and fibrils are immersed in an amorphous substance rich in glycosaminoglycans (mainly keratin sulfates), which ensures the transparency of the cornea's own substance. In the region of the iridocorneal angle, it continues into the opaque outer shell of the eye - the sclera.

The cornea itself does not have blood vessels.

Posterior border plate ( lamina limitans posterior) - Descemet's membrane - 5-10 microns thick, represented by collagen fibers with a diameter of 10 nm, immersed in an amorphous substance. This is a glassy membrane that strongly refracts light. It consists of 2 layers: the outer - elastic, the inner - cuticular and is a derivative of cells of the posterior epithelium ("endothelium"). The characteristic features of Descemet's membrane are strength, resistance to chemical agents and the melting effect of purulent exudate in corneal ulcers.

When the anterior layers die, Desmet's membrane protrudes into a transparent vesicle (descemetocele).

At the periphery it thickens, and in elderly people, round warty formations - Hassall-Henle bodies - can form in this place.

At the limbus, Descemet's membrane, becoming thinner and becoming more fibrous, passes into the trabeculae of the sclera.

"Corneal endothelium", or posterior epithelium ( epithelium posterius), consists of a single layer of flat polygonal cells. It protects the corneal stroma from exposure to anterior chamber moisture. The nuclei of endothelial cells are round or slightly oval, their axis is parallel to the surface of the cornea.

Endothelial cells often contain vacuoles. At the periphery, the “endothelium” passes directly onto the fibers of the trabecular meshwork, forming the outer cover of each trabecular fiber, stretching in length.

Bowman's and Descemet's membranes play a role in the regulation of water metabolism, and metabolic processes in the cornea are ensured by diffusion nutrients from the anterior chamber of the eye due to the marginal looped network of the cornea, with numerous terminal capillary branches forming a dense perilimbal plexus.

The lymphatic system of the cornea is formed from narrow lymphatic slits communicating with the ciliary venous plexus.

The cornea is highly sensitive due to the presence of nerve endings in it.

Long ciliary nerves, representing branches of the nasociliary nerve arising from the first branch trigeminal nerve, on the periphery of the cornea penetrate into its thickness, lose myelin at some distance from the limbus, dividing dichotomously.

The nerve branches form the following plexuses: in the substance of the cornea, preterminal and under Bowman's membrane - terminal, subbasal (Riser's plexus).

During inflammatory processes, blood capillaries and cells (leukocytes, macrophages, etc.) penetrate from the limbus into the cornea's own substance, which leads to its clouding and keratinization, the formation of a cataract.

Anterior chamber of the eye formed by the cornea (outer wall) and the iris (posterior wall), in the area of the pupil - by the anterior capsule of the lens.

At its extreme periphery in the corner of the anterior chamber there is a chamber, or iridocorneal, angle ( spatia anguli iridocornealis) with a small portion of the ciliary body. The chamber (also called filtration) corner borders the drainage apparatus - the Schlemm canal. The state of the chamber angle plays a large role in the exchange of intraocular fluid and in changes in intraocular pressure. Corresponding to the apex of the angle, a ring-shaped groove passes through the sclera ( sulcus sclerae interims).

The posterior edge of the groove is somewhat thickened and forms a scleral ridge formed by circular fibers of the sclera (posterior limiting ring of Schwalbe). The scleral ridge serves as the attachment point for the suspensory ligament of the ciliary body and the iris - the trabecular apparatus that fills the anterior part of the scleral groove.

In the posterior part it covers Schlemm's canal.

Trabecular apparatus, previously erroneously called the pectineal ligament, consists of 2 parts: sclerocorneal ( lig. sclerocorneale), occupying most of the trabecular apparatus, and the second, more delicate, uveal part, which is located with inside and is the pectineal ligament proper ( lig.

pectinatum). The sclerocorneal section of the trabecular apparatus is attached to the scleral spur and partially merges with the ciliary muscle (Brücke's muscle). The sclerocorneal part of the trabecular apparatus consists of a network of interwoven trabeculae with a complex structure. In the center of each trabecula, which is a flat thin cord, there passes a collagen fiber, entwined, reinforced with elastic fibers and covered on the outside with a case of a homogeneous vitreous membrane, which is a continuation of Descemet’s membrane.

Between the complex interweaving of corneoscleral fibers there remain numerous free slit-like openings - fountain spaces, lined with “endothelium” passing from the posterior surface of the cornea. The Fontan spaces are directed to the wall of the venous sinus of the sclera (sinus venosus sclerae) - Schlemm's canal, located in the lower part of the scleral groove 0.25 cm wide.

In some places it divides into a number of tubules, which then merge into one trunk. The inside of Schlemm's canal is lined with endothelium. Wide, sometimes varicose vessels extend from its outer side, forming a complex network of anastomoses, from which veins originate, draining chamber moisture into the deep scleral venous plexus.

Lens (lens). This is a transparent biconvex lens, the shape of which changes during the eye's accommodation to seeing near or distant objects.

Together with the cornea and vitreous body, the lens constitutes the main light-refracting medium. The radius of curvature of the lens varies from 6 to 10 mm, the refractive index is 1.42.

The lens is covered with a transparent capsule 11-18 microns thick. Its anterior wall consists of a single-layer squamous epithelium of the lens ( epithelium lentis).

Towards the equator, epithelial cells become taller and form the growth zone of the lens. This zone “supplies” new cells throughout life to both the anterior and posterior surfaces of the lens.

New epithelial cells are transformed into so-called lens fibers ( fibrae lentis). Each fiber is a transparent hexagonal prism.

Visual analyzer. Light refractive structures of the eye

In the cytoplasm of the lens fibers there is a transparent protein - crystallin. The fibers are glued together with a special substance that has the same refractive index as them.

The centrally located fibers lose their nuclei and, overlapping each other, form the nucleus of the lens.

The lens is supported in the eye by the fibers of the ciliary band ( zonula ciliaris), formed by radially arranged bundles of inextensible fibers attached on one side to the ciliary body, and on the other to the lens capsule, due to which the contraction of the muscles of the ciliary body is transmitted to the lens. Knowledge of the laws of the structure and histophysiology of the lens made it possible to develop methods for creating artificial lenses and widely introduce their transplantation into clinical practice, which made possible treatment patients with clouding of the lens (cataract).

Vitreous body (corpus vitreum).

This is a transparent jelly-like mass that fills the cavity between the lens and the retina. On fixed preparations, the vitreous body has a mesh structure. At the periphery it is denser than in the center. A canal passes through the vitreous body - a remnant of the embryonic vascular system of the eye - from the retinal papilla to the posterior surface of the lens. The vitreous contains protein vitrein and hyaluronic acid. The refractive index of the vitreous body is 1.33.

7.5.2. Light-conducting media of the eye and refraction of light (refraction)

The eyeball is a spherical chamber with a diameter of about 2.5 cm containing light-conducting media - the cornea, the moisture of the anterior chamber, the lens and the gelatinous fluid - the vitreous body, the purpose of which is to refract light rays and focus them in the area where the receptors are located on the retina.

The walls of the chamber are three shells. The outer opaque shell - the sclera - passes from the front into the transparent cornea. The middle choroid at the front of the eye forms the ciliary body and the iris, which determines the color of the eyes. In the middle of the iris (iris) there is a hole - the pupil, which regulates the amount of light rays transmitted. The diameter of the pupil is regulated by the pupillary reflex, the center of which is located in the midbrain. The inner retina (retina), or retina, contains the photoreceptors of the eye - rods and cones - and serves to convert light energy into nervous excitement. The light refractive media of the eye, refracting light rays, provide sharp image on the retina.

The main refractive media of the human eye are the cornea and lens. Rays coming from infinity through the center of the cornea and lens (i.e., through the main optical axis of the eye) perpendicular to their surface do not experience refraction. All other rays are refracted and converge inside the chamber of the eye at one point - the focus. The adaptation of the eye to clearly seeing objects at different distances (its focusing) is called accommodation. This process in humans is carried out by changing the curvature of the lens. The closest point of clear vision moves away with age (from 7 cm at 7-10 years to 75 cm at 60 years or more), as the elasticity of the lens decreases and accommodation deteriorates. Senile farsightedness occurs.

Normally, the length of the eye corresponds to the refractive power of the eye. However, 35% of people have violations of this correspondence. In case of myopia, the length of the eye is longer than normal and the rays are focused in front of the retina, and the image on the retina becomes blurry. In a farsighted eye, on the contrary, the length of the eye is less than normal and the focus is located behind the retina. As a result, the image on the retina is also blurry.

The inner core of the eye consists of transparent light-refracting media: the vitreous body, the lens, intended for constructing an image on the retina, and aqueous humor, which fills the eye chambers and serves to nourish the avascular formations of the eye.

A. The vitreous body, corpus vitreum, forms the cavity of the eyeball medially from the retina and is a completely transparent mass, similar to jelly, lying behind the lens. Thanks to the depression from the latter, a fossa is formed on the anterior surface of the vitreous body - fossa hyaloidea, the edges of which are connected to the lens capsule through a special ligament.

B. The lens, or lens, is a very significant light-refracting medium of the eyeball. It is completely transparent and has the appearance of lentils or biconvex glass. Center points the anterior and posterior surfaces are called poles (polus anterior et posterior), and the peripheral edge of the lens, where both surfaces meet each other, is called the equator. The axis of the lens connecting both poles is 3.7 mm when looking at distance and 4.4 mm during accommodation, when the lens becomes more convex. Equatorial diameter 9 mm. The lens, with the plane of its equator, stands at a right angle to the optical axis, adjoining its anterior surface to the iris, and its posterior surface to the vitreous body.

The lens is enclosed in a thin, also completely transparent, structureless capsule, capsula lentis, and is held in its position by a special ligament - the ciliary girdle, zonula ciliaris, which is made up of many thin fibers running from the lens capsule to the ciliary body, where they lie mainly between the ciliary processes . Between the fibers of the ligament there are fluid-filled spaces of the girdle, spatia zonularia, communicating with the chambers of the eye.

Thanks to the elasticity of its capsule, the lens easily changes its curvature depending on whether we look far or near. This phenomenon is called accommodation. In the first case, the lens is somewhat flattened due to the tension of the ciliary band; in the second, when the eye must be set on close quarters, the ciliary belt, under the influence of contraction of the m.ciliaris, weakens along with the lens capsule and the latter becomes more convex. Thanks to this, rays coming from a nearby object are refracted more strongly by the lens and can connect on the retina. The lens, like the vitreous body, does not have blood vessels.

B. Chambers of the eye. The space located between the anterior surface of the iris and the posterior side of the cornea is called the anterior chamber of the eyeball, camera anterior bulbi. Front and back wall the chambers come together along its circumference in the angle formed by the transition of the cornea into the sclera, on the one hand, and the ciliary edge of the iris, on the other. This angle, angulus iridocornealis, is rounded by a network of crossbars.

Between the crossbars there are slot-like spaces. Angulus iridocornealis has an important physiological significance in terms of the circulation of fluid in the chamber, which, through the indicated spaces, is emptied into the venous sinus located nearby in the thickness of the sclera.

Behind the iris there is a narrower posterior chamber of the eye, camera posterior bulbi, which also includes the spaces between the fibers of the ciliary girdle; behind it is limited by the lens, and on the side by the corpus ciliare. Through the pupil, the posterior chamber communicates with the anterior one. Both chambers of the eye are filled with a transparent liquid - aqueous humor, humor aquosus, the outflow of which occurs into the venous sinus of the sclera.

Ticket number 7

Human anatomy and age. Peculiarities of the structure of organs and bodies in adolescent children, in adolescence, adulthood, old age and senility. Examples.

Age anatomy studies the structure of a person at different age periods. Under the influence of age and external factors The structure and shape of human organs changes with a certain pattern. In children of the first years of life, adults and older people, there are significant differences in anatomical structure body. In clinical practice there have even arisen independent disciplines, for example, pediatrics is the science of the child, gerontology is the science of the elderly.

Examples:

Three main periods can be traced in the growth of the skull after birth. The first period - up to 7 years of age - is characterized by vigorous growth of the skull, especially in the occipital part.

In the 1st year of a child’s life, the thickness of the skull bones increases approximately 3 times, the outer and inner plates begin to form in the bones of the vault, with diploe between them. The mastoid process of the temporal bone develops and in it - mastoid cells. In growing bones, ossification points continue to merge, forming a bony external auditory canal, which closes into a bone ring by the age of 5. By the age of 7, the fusion of parts of the frontal bone ends, parts of the ethmoid bone grow together.

In the second period, from 7 years to the onset of puberty, slow but uniform growth of the skull occurs, especially in the area of its base. The volume of the cerebral part of the skull reaches 1300 cm 3 by the age of 10. At this age, the fusion of individual parts of the skull bones, developing from independent ossification points, is basically complete.

The third period - from 13 to 20-23 years - is characterized by intensive growth, mainly of the facial part of the skull, and the appearance of sexual differences. After 13 years, further thickening of the skull bones occurs; Pneumatization of the bones continues, as a result of which the mass of the skull is relatively reduced while maintaining its strength. By the age of 20, the sutures between the sphenoid and occipital bones ossify. The growth of the base of the skull in length ends by this period.

After 20 years, especially after 30 years, the sutures of the cranial vault heal. The sagittal suture in its posterior part begins to heal first (22-35 years), then the coronal suture in the middle part (24-42 years), mastoid-occipital (30-81 years); scaly rarely overgrows. In old age, the bones of the skull become thinner and more fragile.

Sections