Age dynamics of visual functions. Visual functions and age-related dynamics of their development Age-related features of the organ of vision

A newborn is born with a system of visual perception that is very different from that of an adult. In the future, both the optical apparatus and those organs that are responsible for receiving the “image” and its interpretation by the brain undergo very significant changes. Despite the fact that the development process is completely completed by the age of 20-25, the most large-scale changes in the organs of vision occur in the first year of a child's life.

Features of vision in young children

During the entire period of intrauterine development, the baby's organs of vision are practically not needed. After birth, the system of visual perception begins to develop rapidly. The main changes are:

• Eyeball. In a newborn, it looks like a ball, strongly flattened horizontally and elongated vertically. As it grows, the shape of the eye approaches spherical;
• Cornea. The thickness of the main refractive disc in the center of a baby in the first months of life is 1.5 mm, the diameter is about 8 mm, and the radius of surface curvature is about 7 mm. The growth of the cornea occurs due to the stretching of the tissue that forms it. As a result, as the child grows older, this organ becomes wider, thinner and acquires a more rounded surface. In addition, the cornea of ​​the newborn is almost devoid of sensitivity due to the weak development of some cranial nerves. Over time, this parameter also returns to normal;
• The lens of the baby is an almost regular ball. The development of this most important element of the optical system follows the path of flattening and transformation into a biconvex lens;
• Pupil and iris. A feature of vision in children who have just been born is the lack of a coloring pigment in the body - melanin. Therefore, the iris in babies, as a rule, is light (bluish-grayish). The muscles responsible for the expansion of the pupil are poorly developed; Normally, the pupil in newborns is narrow;
• The main element of the visual analyzer is the retina, in children of the first months of life it consists of ten layers with different structures, and has a very low resolution. By the age of six months, the retina is stretched, six layers out of ten become thinner and completely disappear. A yellow spot is formed - a zone of optimal focusing of light rays;
• The anterior chamber of the eye (the space between the cornea and the surface of the iris) deepens and expands in the first years of life;
• Bones of the skull that form the eye socket. In babies, the cavities in which the eyeballs are located are not deep enough. Because of this, the axes of the eyes are oblique, and there is such a feature of vision in children as the appearance of convergent strabismus.

Some children are born with defects in the eyelids, as well as the lacrimal glands or tear ducts. In the future, this can lead to the development of pathologies of vision.

Features of vision in children of different ages

The specificity of the structure of the visual apparatus of the newborn is the reason that the baby sees poorly. Over time, the image perception system improves, and vision defects are corrected:

• A change in the configuration of the eyeball leads to the correction of congenital farsightedness, which is observed in the vast majority of newborns (about 93%). In most three-year-old children, the shape of the eyes is almost the same as in adults;
• Normal innervation of the cornea occurs already in a one-year-old child (by 12 months, the corresponding cranial nerves are fully developed). The geometric parameters of the cornea (diameter, radius of curvature, thickness) are finally formed by the age of seven. At the same time, the refractive power of this element of the optical system is optimized, physiological astigmatism disappears;
• The muscles that dilate the pupil acquire the ability to work normally when the baby is 1-3 years old (this is a very individual process). The content of melanin in the body also increases in all children in different ways, so the color of the iris can remain unstable up to 10-12 years;
• Changes in the shape of the lens occur in humans throughout life. For babies, the decisive moment is the formation of the habit of accommodation (the ability to focus the gaze at various distances), which occurs in the first months of life. In addition, with the development of the lens, its refractive power increases;
• Optimization of the size and shape of the orbit due to the growth of the bones of the skull, which is completed by 8-10 years.

The main feature of vision in children is the congenital imperfection of the optical apparatus and the image interpretation system. If the development of the crumbs is normal, by the age of three months he receives the skills of spatial perception, by six months he is able to see objects in a three-dimensional image and perfectly distinguishes colors. Visual acuity, which is very low in toddlers, reaches the level characteristic of adults by about 5-7 years.

The organ of vision in its development has gone from separate ectodermal origin of light-sensitive cells (in intestinal cavities) to complex paired eyes in mammals. Vertebrates have complex eyes. From the lateral outgrowths of the brain, a light-sensitive membrane is formed - the retina. The middle and outer shells of the eyeball, the vitreous body are formed from the mesoderm (middle germinal layer), the lens - from the ectoderm.

The inner shell (retina) is shaped like a double-walled glass. The pigment part (layer) of the retina develops from the thin outer wall of the glass. Visual (photoreceptor, light-sensitive) cells are located in the thicker inner layer of the glass. In fish, the differentiation of visual cells into rod-shaped (rods) and cone-shaped (cones) is weakly expressed, in reptiles there are only cones, in mammals in the retina - mainly rods. In aquatic and nocturnal animals, cones are absent in the retina. As part of the middle (vascular) membrane, the ciliary body is already formed in fish, which becomes more complicated in its development in birds and mammals.

Muscles in the iris and ciliary body first appear in amphibians. The outer shell of the eyeball in lower vertebrates consists mainly of cartilaginous tissue (in fish, partly in amphibians, in most reptiles and monotremes). In mammals, the outer shell is built only from fibrous (fibrous) tissue. The anterior part of the fibrous membrane (cornea) is transparent. The lens of fish and amphibians is rounded. Accommodation is achieved due to the movement of the lens and the contraction of a special muscle that moves the lens. In reptiles and birds, the lens is able not only to move, but also to change its curvature. In mammals, the lens occupies a permanent place. Accommodation is due to a change in the curvature of the lens. The vitreous body, which initially has a fibrous structure, gradually becomes transparent.

Simultaneously with the complication of the structure of the eyeball, auxiliary organs of the eye develop. The first to appear are six oculomotor muscles, which are transformed from the myotomes of three pairs of head somites. Eyelids begin to form in fish in the form of a single annular skin fold. In terrestrial vertebrates, upper and lower eyelids are formed. In most animals, there is also a nictitating membrane (third eyelid) at the medial corner of the eye. The remnants of this membrane are preserved in monkeys and humans in the form of a semilunar fold of the conjunctiva. In terrestrial vertebrates, the lacrimal gland develops, and the lacrimal apparatus is formed.

The human eyeball also develops from several sources. The light-sensitive membrane (retina) comes from the side wall of the brain bladder (the future diencephalon); the main lens of the eye - the lens - directly from the ectoderm, the vascular and fibrous membranes - from the mesenchyme. At an early stage of embryo development (the end of the 1st - the beginning of the 2nd month of intrauterine life), a small paired protrusion appears on the side walls of the primary brain bladder - eye bubbles. Their terminal sections expand, grow towards the ectoderm, and the legs connecting with the brain narrow and later turn into optic nerves. In the process of development, the wall of the optic vesicle protrudes into it and the vesicle turns into a two-layer ophthalmic cup. The outer wall of the glass further becomes thinner and transforms into the outer pigment part (layer), and the complex light-perceiving (nervous) part of the retina (photosensory layer) is formed from the inner wall. At the stage of formation of the eyecup and differentiation of its walls, at the 2nd month of intrauterine development, the ectoderm adjacent to the eyecup in front thickens at first, and then a lens fossa is formed, which turns into a lens vesicle. Separated from the ectoderm, the vesicle plunges into the eye cup, loses the cavity, and the lens is subsequently formed from it.

At the 2nd month of intrauterine life, mesenchymal cells penetrate into the eye cup through the gap formed on its lower side. These cells form a blood vascular network inside the glass in the vitreous body that is forming here and around the growing lens. From the mesenchymal cells adjacent to the eye cup, the choroid is formed, and from the outer layers, the fibrous membrane. The anterior part of the fibrous membrane becomes transparent and turns into the cornea. In a fetus of 6-8 months, the blood vessels located in the lens capsule and the vitreous body disappear; the membrane covering the opening of the pupil (pupillary membrane) is resorbed.

Upper and lower eyelids begin to form on the 3rd month of intrauterine life, at first in the form of ectoderm folds. The epithelium of the conjunctiva, including the one that covers the front of the cornea, comes from the ectoderm. The lacrimal gland develops from outgrowths of the conjunctival epithelium that appear on the 3rd month of intrauterine life in the lateral part of the emerging upper eyelid.

Eyeball the newborn is relatively large, its anteroposterior size is 17.5 mm, weight - 2.3 g. The visual axis of the eyeball runs more lateral than in an adult. The eyeball grows in the first year of a child's life faster than in subsequent years. By the age of 5, the mass of the eyeball increases by 70%, and by the age of 20-25 - 3 times compared with a newborn.

Cornea in a newborn, it is relatively thick, its curvature almost does not change during life; the lens is almost round, the radii of its anterior and posterior curvature are approximately equal. The lens grows especially rapidly during the first year of life, and then its growth rate decreases. iris convex anteriorly, there is little pigment in it, the pupil diameter is 2.5 mm. As the age of the child increases, the thickness of the iris increases, the amount of pigment in it increases, and the diameter of the pupil becomes large. At the age of 40-50 years, the pupil narrows slightly.

ciliary body the newborn is poorly developed. The growth and differentiation of the ciliary muscle is quite fast. The optic nerve in a newborn is thin (0.8 mm), short. By the age of 20, its diameter almost doubles.

Muscles of the eyeball in a newborn, they are developed quite well, except for their tendon part. Therefore, eye movements are possible immediately after birth, but the coordination of these movements is only from the 2nd month of life.

Lacrimal gland in a newborn it is small, the excretory tubules of the gland are thin. The function of tearing appears on the 2nd month of a child's life. The vagina of the eyeball in a newborn and infants is thin, the fatty body of the orbit is poorly developed. In elderly and senile people, the fat body of the orbit decreases in size, partially atrophies, the eyeball protrudes less from the orbit.

The human eyeball develops from several sources. The light-sensitive membrane (retina) comes from the side wall of the cerebral bladder (the future diencephalon), the lens comes from the ectoderm, the vascular and fibrous membranes come from the mesenchyme. At the end of the 1st, beginning of the 2nd month of intrauterine life, a small paired protrusion appears on the side walls of the primary cerebral bladder - eye blisters. In the process of development, the wall of the optic vesicle protrudes into it and the vesicle turns into a two-layer ophthalmic cup. The outer wall of the glass further becomes thinner and is converted into an outer

pigment part (layer). A complex light-perceiving (nervous) part of the retina (photosensory layer) is formed from the inner wall of this bubble. At the 2nd month of intrauterine development, the ectoderm adjacent to the eye cup thickens, then a lens fossa forms in it, turning into a crystal bubble. Separated from the ectoderm, the vesicle plunges into the eye cup, loses the cavity, and the lens is subsequently formed from it.

At the 2nd month of intrauterine life, mesenchymal cells penetrate into the eye cup, from which the blood vascular network and the vitreous body are formed inside the glass. From the mesenchymal cells adjacent to the eye cup is formed; choroid, and from the outer layers - the fibrous membrane. The anterior part of the fibrous membrane becomes transparent and turns into the cornea. In a fetus of 6-8 months, the blood vessels located in the lens capsule and the vitreous body disappear; the membrane covering the opening of the pupil (pupillary membrane) is resorbed.

The upper and lower eyelids begin to form in the 3rd month of intrauterine life, initially in the form of ectoderm folds. The epithelium of the conjunctiva, including the one that covers the front of the cornea, comes from the ectoderm. The lacrimal gland develops / from outgrowths of the conjunctival epithelium in the lateral part of the emerging upper eyelid.

The eyeball of a newborn is relatively large, his; the anteroposterior size is 17.5 mm, weight - 2.3 g. By the age of 5, the mass of the eyeball increases by 70%, and by 20-25 years - 3 times compared with a newborn.

The cornea of ​​a newborn is relatively thick, its curvature almost does not change during life. The lens is almost round. The lens grows especially rapidly during the first year of life, and then its growth rate decreases. The iris is convex anteriorly, there is little pigment in it, the pupil diameter is 2.5 mm. As the age of the child increases, the thickness of the iris increases, the amount of pigment in it increases, and the diameter of the pupil becomes large. At the age of 40-50 years, the pupil narrows slightly.

The ciliary body in a newborn is poorly developed. The growth and differentiation of the ciliary muscle is quite fast.

The muscles of the eyeball in a newborn are well developed, except for their tendon part. Therefore, eye movement is possible immediately after birth, but the coordination of these movements begins from the 2nd month of a child's life.

The lacrimal gland in a newborn is small, the excretory ducts of the gland are thin. The function of tearing appears on the 2nd month of a child's life. The fatty body of the orbit is poorly developed. In elderly and senile people, the fat body of the orbit decreases in size, partially atrophies, the eyeball protrudes less from the orbit.

The palpebral fissure in a newborn is narrow, the medial angle of the eye is rounded. In the future, the palpebral fissure rapidly increases. In children under 14-15 years old, it is wide, so the eye seems larger than in an adult.

Anomalies in the development of the eyeball.

The complex development of the eyeball leads to birth defects. More often than others, an irregular curvature of the cornea or lens occurs, as a result of which the image on the retina is distorted (astigmatism). When the proportions of the eyeball are disturbed, congenital myopia (the visual axis is elongated) or hyperopia (the visual axis is shortened) appear. A gap in the iris (coloboma) often occurs in its anteromedial segment. The remnants of the branches of the artery of the vitreous body interfere with the passage of light in the vitreous body. Sometimes there is a violation of the transparency of the lens (congenital cataract). Underdevelopment of the venous sinus of the sclera (Schlemm's canal) or spaces of the iridocorneal angle (fountain spaces) causes congenital glaucoma.

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• Introduction 2
• 1. Organ of vision 3
• 8
• 12
• 13
• Conclusion 15
• Literature 16

Introduction

The relevance of the topic of our work is obvious. The organ of vision, organum visus, plays an important role in a person's life, in his communication with the external environment. In the process of evolution, this organ has gone from light-sensitive cells on the surface of the animal's body to a complex organ capable of moving in the direction of the light beam and sending this beam to special light-sensitive cells in the thickness of the back wall of the eyeball, which perceive both black and white and color image. Having reached perfection, the organ of vision in a person captures pictures of the external world, transforms light irritation into a nerve impulse.

The organ of vision is located in the orbit and includes the eye and auxiliary organs of vision. With age, certain changes occur in the organs of vision, which leads to a general deterioration in a person's well-being, to social and psychological problems.

The purpose of our work is to find out what age-related changes in the organs of vision are.

The task is to study and analyze the literature on this topic.

1. Organ of vision

The eye, oculus (Greek ophthalmos), consists of the eyeball and the optic nerve with its membranes. Eyeball, bulbus oculi, rounded. The poles are distinguished in it - anterior and posterior, polus anterior et polus posterior. The first corresponds to the most protruding point of the cornea, the second is located lateral to the exit point of the optic nerve from the eyeball. The line connecting these points is called the outer axis of the eye, axis bulbi externus. It is approximately 24 mm and is located in the plane of the meridian of the eyeball. The internal axis of the eyeball, axis bulbi internus (from the posterior surface of the cornea to the retina), is 21.75 mm. In the presence of a longer internal axis, the rays of light, after being refracted in the eyeball, are concentrated in front of the retina. At the same time, good vision of objects is possible only at close distances - myopia, myopia (from the Greek myops - squinting eye). The focal length of myopic people is shorter than the inner axis of the eyeball.

If the inner axis of the eyeball is relatively short, then the rays of light after refraction are collected in focus behind the retina. Distance vision is better than near - farsightedness, hypermetropia (from the Greek metron - measure, ops - gender, opos - vision). The focal length of the far-sighted is longer than the inner axis of the eyeball.

The vertical size of the eyeball is 23.5 mm, and the transverse size is 23.8 mm. These two dimensions are in the plane of the equator.

Allocate the visual axis of the eyeball, axis opticus, which extends from its anterior pole to the central fossa of the retina - the point of best vision. (Fig. 202).

The eyeball consists of the membranes that surround the nucleus of the eye (aqueous humor in the anterior and posterior chambers, the lens, the vitreous body). There are three membranes: external fibrous, middle vascular and internal sensitive.

The fibrous membrane of the eyeball, tunica fibrosa bulbi, performs a protective function. The front part of it is transparent and is called the cornea, and the large back part, because of the whitish color, is called the albuginea, or sclera. The boundary between the cornea and the sclera is a shallow circular sulcus of the sclera, sulcus sclerae.

The cornea, cornea, is one of the transparent media of the eye and is devoid of blood vessels. It has the appearance of an hour glass, convex in front and concave in the back. Corneal diameter - 12 mm, thickness - about 1 mm. The peripheral edge (limb) of the cornea, limbus corneae, is, as it were, inserted into the anterior part of the sclera, into which the cornea passes.

Sclera, sclera, consists of dense fibrous connective tissue. In its back part there are numerous openings through which bundles of optic nerve fibers exit and vessels pass. The thickness of the sclera at the exit of the optic nerve is about 1 mm, and in the region of the equator of the eyeball and in the anterior section - 0.4-0.6 mm. On the border with the cornea in the thickness of the sclera lies a narrow circular canal filled with venous blood - the venous sinus of the sclera, sinus venosus sclerae (Schlemm's canal).

The choroid of the eyeball, tunica vasculosa bulbi, is rich in blood vessels and pigment. It is directly adjacent to the sclera from the inside, with which it is firmly fused at the exit from the eyeball of the optic nerve and at the border of the sclera with the cornea. The choroid is divided into three parts: the choroid proper, the ciliary body, and the iris.

The choroid itself, the choroidea, lines the large posterior part of the sclera, with which, in addition to the indicated places, it is loosely fused, limiting from the inside the so-called perivascular space, spatium perichoroideale, existing between the membranes.

The ciliary body, corpus ciliare, is a middle thickened section of the choroid, located in the form of a circular roller in the region of the transition of the cornea to the sclera, behind the iris. The ciliary body is fused with the outer ciliary edge of the iris. The back of the ciliary body - the ciliary circle, orbiculus ciliaris, has the form of a thickened circular strip 4 mm wide, passes into the choroid itself. The anterior part of the ciliary body forms about 70 radially oriented folds, thickened at the ends, up to 3 mm long each - ciliary processes, processus ciliares. These processes consist mainly of blood vessels and make up the ciliary crown, corona ciliaris.

In the thickness of the ciliary body lies the ciliary muscle, m. ciliaris, consisting of intricately intertwined bundles of smooth muscle cells. When the muscle contracts, accommodation of the eye occurs - an adaptation to a clear vision of objects located at different distances. In the ciliary muscle, meridional, circular and radial bundles of unstriated (smooth) muscle cells are isolated. Meridional (longitudinal) fibers, fibrae meridionales (longitudinales), of this muscle originate from the edge of the cornea and from the sclera and are woven into the anterior part of the choroid itself. With their contraction, the shell shifts anteriorly, as a result of which the tension of the ciliary band, zonula ciliaris, on which the lens is attached, decreases. In this case, the lens capsule relaxes, the lens changes its curvature, becomes more convex, and its refractive power increases. Circular fibers, fibrae circulares, starting together with the meridional fibers, are located medially from the latter in a circular direction. With its contraction, the ciliary body is narrowed, bringing it closer to the lens, which also contributes to the relaxation of the lens capsule. Radial fibers, fibrae radiales, start from the cornea and sclera in the region of the iridocorneal angle, are located between the meridional and circular bundles of the ciliary muscle, bringing these bundles together during their contraction. The elastic fibers present in the thickness of the ciliary body straighten the ciliary body when its muscles are relaxed.

The iris, iris, is the most anterior part of the choroid, visible through the transparent cornea. It has the form of a disk about 0.4 mm thick, placed in the frontal plane. In the center of the iris there is a round hole - the pupil, pirilla. The pupil diameter is variable: the pupil constricts in strong light and expands in the dark, acting as the diaphragm of the eyeball. The pupil is limited by the pupillary edge of the iris, margo pupillaris. The outer ciliary edge, margo ciliaris, is connected to the ciliary body and to the sclera with the help of the comb ligament, lig. pectinatum iridis (BNA). This ligament fills the iridocorneal angle formed by the iris and cornea, angulus iridocornealis. The anterior surface of the iris faces the anterior chamber of the eyeball, and the posterior surface faces the posterior chamber and lens. The connective tissue stroma of the iris contains blood vessels. The cells of the posterior epithelium are rich in pigment, the amount of which determines the color of the iris (eye). In the presence of a large amount of pigment, the color of the eye is dark (brown, hazel) or almost black. If there is little pigment, then the iris will have a light gray or light blue color. In the absence of pigment (albinos), the iris is reddish in color, as blood vessels shine through it. Two muscles lie in the thickness of the iris. Around the pupil, bundles of smooth muscle cells are circularly located - the sphincter of the pupil, m. sphincter pupillae, and radially from the ciliary edge of the iris to its pupillary edge extend thin bundles of the muscle that dilates the pupil, m. dilatator pupillae (pupil dilator).

The inner (sensitive) shell of the eyeball (retina), tunica interna (sensoria) bulbi (retina), is tightly attached from the inside to the choroid along its entire length, from the exit of the optic nerve to the edge of the pupil. In the retina, which develops from the wall of the anterior cerebral bladder, two layers (leaves) are distinguished: the outer pigment part, pars pigmentosa, and the complex internal photosensitive part, called the nervous part, pars nervosa. Accordingly, the functions distinguish a large posterior visual part of the retina, pars optica retinae, containing sensitive elements - rod-shaped and cone-shaped visual cells (rods and cones), and a smaller, "blind" part of the retina, devoid of rods and cones. The "blind" part of the retina combines the ciliary part of the retina, pars ciliaris retinae, and the iris part of the retina, pars iridica retinae. The boundary between the visual and "blind" parts is the jagged edge, ora serrata, which is clearly visible on the preparation of the opened eyeball. It corresponds to the place of transition of the choroid itself into the ciliary circle, orbiculus ciliaris, choroid.

In the posterior part of the retina at the bottom of the eyeball in a living person, using an ophthalmoscope, you can see a whitish spot with a diameter of about 1.7 mm - the optic disc, discus nervi optici, with raised edges in the form of a roller and a small depression, excavatio disci, in the center (Fig. 203).

The disc is the exit point of the optic nerve fibers from the eyeball. The latter, being surrounded by membranes (continuation of the membranes of the brain), forming the outer and inner sheaths of the optic nerve, vagina externa et vagina interna n. optici, is directed towards the optic canal, which opens into the cranial cavity. Due to the absence of light-sensitive visual cells (rods and cones), the disc area is called the blind spot. In the center of the disk, its central artery entering the retina is visible, a. centralis retinae. Lateral to the optic disc by about 4 mm, which corresponds to the posterior pole of the eye, there is a yellowish spot, macula, with a small depression - the central fossa, fovea centralis. The fovea is the place of the best vision: only cones are concentrated here. There are no sticks in this place.

The inner part of the eyeball is filled with aqueous humor located in the anterior and posterior chambers of the eyeball, the lens and the vitreous body. Together with the cornea, all these formations are the light-refracting media of the eyeball. The anterior chamber of the eyeball, camera anterior bulbi, containing aqueous humor, humor aquosus, is located between the cornea in front and the anterior surface of the iris behind. Through the opening of the pupil, the anterior chamber communicates with the posterior chamber of the eyeball, camera posterior bulbi, which is located behind the iris and bounded behind by the lens. The posterior chamber communicates with the spaces between the fibers of the lens, the fibrae zonulares, which connect the lens sac to the ciliary body. Girdle spaces, spatia zonularia, look like a circular fissure (petite canal) lying along the periphery of the lens. They, like the posterior chamber, are filled with aqueous humor, which is formed with the participation of numerous blood vessels and capillaries that lie in the thickness of the ciliary body.

Located behind the chambers of the eyeball, the lens, lens, has the shape of a biconvex lens and has a large light refractive power. The anterior surface of the lens, facies anterior lentis, and its most protruding point, the anterior pole, polus anterior, face the posterior chamber of the eyeball. The more convex posterior surface, facies posterior, and the posterior pole of the lens, polus posterior lentis, are adjacent to the anterior surface of the vitreous body. The vitreous body, corpus vitreum, covered along the periphery with a membrane, is located in the vitreous chamber of the eyeball, camera vitrea bulbi, behind the lens, where it is tightly adjacent to the inner surface of the retina. The lens is, as it were, pressed into the anterior part of the vitreous body, which in this place has a depression called the vitreous fossa, fossa hyaloidea. The vitreous body is a jelly-like mass, transparent, devoid of blood vessels and nerves. The refractive power of the vitreous body is close to the refractive index of the aqueous humor filling the chambers of the eye.

2. Development and age-related features of the organ of vision

The organ of vision in phylogenesis has gone from separate ectodermal origin of light-sensitive cells (in intestinal cavities) to complex paired eyes in mammals. In vertebrates, the eyes develop in a complex way: a light-sensitive membrane, the retina, is formed from the lateral outgrowths of the brain. The middle and outer shells of the eyeball, the vitreous body are formed from the mesoderm (middle germinal layer), the lens - from the ectoderm.

The inner shell (retina) is shaped like a double-walled glass. The pigment part (layer) of the retina develops from the thin outer wall of the glass. Visual (photoreceptor, light-sensitive) cells are located in the thicker inner layer of the glass. In fish, the differentiation of visual cells into rod-shaped (rods) and cone-shaped (cones) is weakly expressed, in reptiles there are only cones, in mammals the retina contains mainly rods; in aquatic and nocturnal animals, cones are absent in the retina. As part of the middle (vascular) membrane, already in fish, the ciliary body begins to form, which becomes more complicated in its development in birds and mammals. Muscles in the iris and in the ciliary body first appear in amphibians. The outer shell of the eyeball in lower vertebrates consists mainly of cartilaginous tissue (in fish, partly in amphibians, in most reptiles and monotremes). In mammals, it is built only from fibrous (fibrous) tissue. The anterior part of the fibrous membrane (cornea) is transparent. The lens of fish and amphibians is rounded. Accommodation is achieved due to the movement of the lens and the contraction of a special muscle that moves the lens. In reptiles and birds, the lens is able not only to move, but also to change its curvature. In mammals, the lens occupies a permanent place, accommodation is carried out due to a change in the curvature of the lens. The vitreous body, which initially has a fibrous structure, gradually becomes transparent.

Simultaneously with the complication of the structure of the eyeball, auxiliary organs of the eye develop. The first to appear are six oculomotor muscles, which are transformed from the myotomes of three pairs of head somites. Eyelids begin to form in fish in the form of a single annular skin fold. Terrestrial vertebrates develop upper and lower eyelids, and most of them also have a nictitating membrane (third eyelid) at the medial corner of the eye. In monkeys and humans, the remnants of this membrane are preserved in the form of a semilunar fold of the conjunctiva. In terrestrial vertebrates, the lacrimal gland develops, and the lacrimal apparatus is formed.

The human eyeball also develops from several sources. The light-sensitive membrane (retina) comes from the side wall of the brain bladder (the future diencephalon); the main lens of the eye - the lens - directly from the ectoderm; vascular and fibrous membranes - from the mesenchyme. At an early stage of development of the embryo (the end of the 1st, the beginning of the 2nd month of intrauterine life), a small paired protrusion appears on the side walls of the primary cerebral bladder (prosencephalon) - eye bubbles. Their terminal sections expand, grow towards the ectoderm, and the legs connecting with the brain narrow and later turn into optic nerves. In the process of development, the wall of the optic vesicle protrudes into it and the vesicle turns into a two-layer ophthalmic cup. The outer wall of the glass further becomes thinner and transforms into the outer pigment part (layer), and the complex light-perceiving (nervous) part of the retina (photosensory layer) is formed from the inner wall. At the stage of formation of the eyecup and differentiation of its walls, at the 2nd month of intrauterine development, the ectoderm adjacent to the eyecup in front thickens at first, and then a lens fossa is formed, which turns into a lens vesicle. Separated from the ectoderm, the vesicle plunges into the eye cup, loses the cavity, and the lens is subsequently formed from it.

At the 2nd month of intrauterine life, mesenchymal cells penetrate into the eye cup through the gap formed on its lower side. These cells form a blood vascular network inside the glass in the vitreous body that is forming here and around the growing lens. From the mesenchymal cells adjacent to the eye cup, the choroid is formed, and from the outer layers, the fibrous membrane. The anterior part of the fibrous membrane becomes transparent and turns into the cornea. The fetus is 6-8 months old. the blood vessels in the lens capsule and in the vitreous disappear; the membrane covering the opening of the pupil (pupillary membrane) is resorbed.

The upper and lower eyelids begin to form in the 3rd month of intrauterine life, initially in the form of ectoderm folds. The epithelium of the conjunctiva, including the one that covers the front of the cornea, comes from the ectoderm. The lacrimal gland develops from outgrowths of the conjunctival epithelium that appear on the 3rd month of intrauterine life in the lateral part of the emerging upper eyelid.

The eyeball of a newborn is relatively large, its anteroposterior size is 17.5 mm, its weight is 2.3 g. The visual axis of the eyeball runs more lateral than in an adult. The eyeball grows in the first year of a child's life faster than in subsequent years. By the age of 5, the mass of the eyeball increases by 70%, and by the age of 20-25 - 3 times compared with a newborn.

The cornea of ​​a newborn is relatively thick, its curvature almost does not change during life; the lens is almost round, the radii of its anterior and posterior curvature are approximately equal. The lens grows especially rapidly during the first year of life, and then its growth rate decreases. The iris is convex anteriorly, there is little pigment in it, the pupil diameter is 2.5 mm. As the age of the child increases, the thickness of the iris increases, the amount of pigment in it increases, and the diameter of the pupil becomes large. At the age of 40-50 years, the pupil narrows slightly.

The ciliary body in a newborn is poorly developed. The growth and differentiation of the ciliary muscle is carried out quite quickly. The optic nerve in a newborn is thin (0.8 mm), short. By the age of 20, its diameter almost doubles.

The muscles of the eyeball in a newborn are well developed, except for their tendon part. Therefore, eye movement is possible immediately after birth, but the coordination of these movements begins from the 2nd month of a child's life.

The lacrimal gland in a newborn is small, the excretory ducts of the gland are thin. The function of tearing appears on the 2nd month of a child's life. The vagina of the eyeball in a newborn and infants is thin, the fatty body of the orbit is poorly developed. In elderly and senile people, the fat body of the orbit decreases in size, partially atrophies, the eyeball protrudes less from the orbit.

The palpebral fissure in a newborn is narrow, the medial angle of the eye is rounded. In the future, the palpebral fissure rapidly increases. In children under 14-15 years old, it is wide, so the eye seems larger than in an adult.

3. Anomalies in the development of the eyeball

The complex development of the eyeball leads to birth defects. More often than others, an irregular curvature of the cornea or lens occurs, as a result of which the image on the retina is distorted (astigmatism). When the proportions of the eyeball are disturbed, congenital myopia (the visual axis is elongated) or hyperopia (the visual axis is shortened) appear. A gap in the iris (coloboma) often occurs in its anteromedial segment.

The remnants of the branches of the artery of the vitreous body interfere with the passage of light in the vitreous body. Sometimes there is a violation of the transparency of the lens (congenital cataract). Underdevelopment of the venous sinus of the sclera (canal schlemms) or spaces of the iridocorneal angle (fountain spaces) causes congenital glaucoma.

4. Determination of visual acuity and its age characteristics

Visual acuity reflects the ability of the optical system of the eye to build a clear image on the retina, that is, it characterizes the spatial resolution of the eye. It is measured by determining the smallest distance between two points, sufficient so that they do not merge, so that the rays from them fall on different receptors in the retina.

The measure of visual acuity is the angle that is formed between the rays coming from two points of the object to the eye - the angle of view. The smaller this angle, the higher the visual acuity. Normally, this angle is 1 minute (1"), or 1 unit. In some people, visual acuity may be less than one. With visual impairments (for example, with myopia), visual acuity deteriorates and becomes greater than one.

Visual acuity improves with age.

In the table parallel rows of letters are arranged horizontally, the size of which decreases from the top row to the bottom. For each row, the distance is determined from which the two points limiting each letter are perceived at an angle of view of 1 ". The letters of the uppermost row are perceived by the normal eye from a distance of 50 meters, and the lower - 5 meters. To determine visual acuity in relative units, the distance, from which the subject can read the line is divided by the distance from which it should be read under the condition of normal vision.

The experiment is carried out as follows.

Place the subject at a distance of 5 meters from the table, which must be well sanctified. Cover one eye of the subject with a screen. Ask the subject to name the letters in the table from top to bottom. Mark the last of the lines that the subject was able to read correctly. By dividing the distance at which the subject is from the table (5 meters) by the distance from which he read the last of the lines he distinguished (for example, 10 meters), find visual acuity. For this example: 5 / 10 = 0.5.

Conclusion

So, in the course of writing our work, we came to the following conclusions:

- The organ of vision develops and changes with the age of a person.

The complex development of the eyeball leads to birth defects. More often than others, an irregular curvature of the cornea or lens occurs, as a result of which the image on the retina is distorted (astigmatism). When the proportions of the eyeball are disturbed, congenital myopia (the visual axis is elongated) or hyperopia (the visual axis is shortened) appear.

The measure of visual acuity is the angle that is formed between the rays coming from two points of the object to the eye - the angle of view. The smaller this angle, the higher the visual acuity. Normally, this angle is 1 minute (1"), or 1 unit. In some people, visual acuity may be less than one. With visual impairments (for example, with myopia), visual acuity deteriorates and becomes greater than one.

Age-related changes in the organ of vision must be studied and controlled, since vision is one of the most important human senses.

Literature

1. M.R. Guseva, I.M. Mosin, T.M. Tskhovrebov, I.I. Bushev. Features of the course of optic neuritis in children. Tez. 3 All-Union Conference on Topical Issues of Pediatric Ophthalmology. M.1989; pp.136-138

2. E.I. Sidorenko, M.R. Guseva, L.A. Dubovskaya. Cerebrolysian in the treatment of partial atrophy of the optic nerve in children. J. Neuropathology and psychiatry. 1995; 95:51-54.

3. M.R. Guseva, M.E. Guseva, O.I. Maslova. Results of the study of the immune status in children with optic neuritis and a number of demyelinating conditions. Book. Age features of the organ of vision in normal and pathological conditions. M., 1992, p.58-61

4. E.I. Sidorenko, A.V. Khvatova, M.R. Guseva. Diagnosis and treatment of optic neuritis in children. Guidelines. M., 1992, 22 p.

5. M.R. Guseva, L.I. Filchikova, I.M. Mosin et al. Electrophysiological methods in assessing the risk of multiple sclerosis in children and adolescents with monosymptomatic optic neuritis J.Neuropatology and psychiatry. 1993; 93:64-68.

6. I.A. Zavalishin, M.N. Zakharova, A.N. Dziuba et al. Pathogenesis of retrobulbar neuritis. J. Neuropathology and Psychiatry. 1992; 92:3-5.

7. I.M. Mosin. Differential and topical diagnosis of optic neuritis in children. Candidate of Medical Sciences (14.00.13) Moscow Research Institute of Eye Diseases. Helmholtz M., 1994, 256 s,

8. M.E. Guseva Clinical and paraclinical criteria for demyelinating diseases in children. Abstract of diss.c.m.s., 1994

9. M.R. Guseva Diagnosis and pathogenetic therapy of uveitis in children. Diss. doctor of medical sciences in the form of a scientific report. M.1996, 63s.

10. IZ Karlova Clinical and immunological features of optic neuritis in multiple sclerosis. Abstract of diss.c.m.s., 1997

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At the age of forty (or a little older), most people begin to feel difficulty when they need to see closely spaced objects - when reading, needlework, and also when working at a computer. Most likely, such visual impairments are associated with age-related changes in the accommodative system of the eyes, which are called presbyopia.

The reasons

Presbyopia is a disease that many people over 40 experience. The lens, located in the eye, performs the important function of accurately focusing surrounding objects that are at different distances. Over time, under the influence of age-related changes, the lens thickens and loses its original elasticity. Because of this, the lens is no longer able to change its curvature, as a result, it is difficult to clearly focus vision on near and distant objects.

The loss of the lens elasticity and ability to change shape distinguishes presbyopia from other visual impairments (farsightedness, myopia, astigmatism), which are mainly due to either genetic or external factors.

Presbyopia is based on natural involutional processes occurring in the organ of vision and leading to a physiological weakening of accommodation. The development of presbyopia is an inevitable age-related process: for example, by the age of 30, the accommodative ability of the eye is reduced by half, by the age of 40 by two-thirds, and by 60 it is almost completely lost.

Accommodation is the ability of the eye to adapt to seeing objects located at different distances. The accommodative mechanism is provided due to the property of the lens to change its refractive power depending on the degree of remoteness of the object and focus its image on the retina.

The main pathogenetic link in presbyopia is sclerotic changes in the lens (phacosclerosis), characterized by its dehydration, compaction of the capsule and nucleus, and loss of elasticity. In addition, with age, the adaptive capabilities of other structures of the eye are also lost. In particular, dystrophic changes develop in the ciliary (ciliary) muscle of the eye that holds the lens. Dystrophy of the ciliary muscle is expressed by the cessation of the formation of new muscle fibers, their replacement by connective tissue, which leads to a weakening of its contractility.

As a result of these changes, the lens loses its ability to increase the radius of curvature when viewing objects located close to the eye. With presbyopia, the point of clear vision gradually moves away from the eye, which is manifested by the difficulty of doing any work near.

Symptoms of presbyopia

Presbyopia is characterized by blurred vision at close range. When you try to better examine objects that are at a short distance (usually closer than 25-30 cm from the eyes), visual fatigue, headaches occur, the situation worsens in low light conditions. Presbyopia is often referred to as the disease of short hands, since most people try to move a small print book (or needlework) away from their eyes to improve visual acuity. But since the disease is progressive, sooner or later this is not enough, and you have to use the appropriate glasses.

Presbyopia can occur against the background of excellent vision, it also does not spare people who are nearsighted or farsighted. People with hypermetropia will experience near vision deterioration at a younger age than those who have had good vision all their lives. Nearsighted people usually develop presbyopia later in life. Impaired near vision in nearsighted people is manifested when wearing distance glasses or contact lenses.

Age-related visual impairment is a problem that is extremely common throughout the world, especially in economically developed countries, where the number of older people is constantly increasing.

The most typical changes are the following:

• Reducing pupil size. The change in pupil size occurs due to the weakening of the muscles responsible for the regulation of the pupils. The main consequence of the reduction of the pupils is the deterioration of their response to the light flux. This means that when the light is not too bright, you will not be able to read, that when you leave a dark house on a street flooded with sunlight, it will take you much longer to get used to the bright light. Older people are much more annoyed by flashes of light than young people, precisely because their eyes have a harder time adjusting to changes in the brightness of the light.
• Deterioration of peripheral vision. It is expressed in the narrowing of the field of view and the deterioration of lateral vision. This feature of vision must be taken into account - especially for people who continue to drive a car even in old age. Also, the deterioration of peripheral vision after 65 years of age can adversely affect those who, by the nature of their activities, need it.
• Increased dryness of the eyes. Dry eye syndrome in old age may not be due to common factors, such as an unhealthy eye strain regimen or being in an environment with a high content of smoke and dust. After 50-55 years, the production of tear fluid decreases, which makes the moisturization of the eyes much worse than at a younger age (this is especially true for women during menopause). Increased dryness can be expressed in redness of the eyes, in tearing under the influence of the wind, in pain in the eyes.
• Deterioration of color recognition. With age, the human eye perceives the world around us more and more dimly, with a decrease in contrast, brightness of the “image”. This happens due to a decrease in the number of retinal cells that perceive color, shades, contrast, brightness. In practice, this effect is felt as if the surrounding world "fades". The ability to recognize shades that are especially close in color (for example, mauve and violet) may also be impaired.

Other age-related eye diseases

Cataract. Cataract is so common among eye diseases today that it can be considered as a natural process of aging of the body. Modern cataract surgery is one of the most high-tech areas in medicine, so effective and safe that it can often restore the patient's previous vision or even surpass it. The appearance of cataract symptoms should prompt you to contact your eye doctor, as timely surgical treatment of cataracts is the key to a minimal risk of complications from the operation.

age-related macular degeneration- is the leading cause of irreversible vision loss among modern pensioners. The population of developed countries is aging at a rapid pace, and the proportion of patients with age-related macular degeneration is steadily increasing, significantly worsening the quality of life.

Glaucoma. On the contrary, this disease begins to get younger, so regular eye examinations for glaucoma are carried out from the age of 40. With every decade of life after age 40, the risk of glaucoma increases many times over.

Diabetic retinopathy. The incidence of diabetes in developed countries is reaching catastrophically threatening levels. One of the first organs affected by diabetic changes is the retina. Regular examinations by an ophthalmologist can detect the earliest changes in the retina and suspect the onset of diabetes in a patient. Diabetic retinopathy causes permanent visual impairment.

Prevention of presbyopia

It is not possible to completely exclude the development of presbyopia - with age, the lens inevitably loses its original properties. In order to delay the onset of presbyopia and slow down the progressive deterioration of vision, it is necessary to avoid excessive visual stress, choose the right lighting, perform gymnastics for the eyes, take vitamin preparations (A, B1, B2, B6, B12, C) and trace elements (Cr, Cu , Mn, Zn etc.).

It is important to visit an ophthalmologist annually, to carry out timely correction of refractive errors, to treat eye diseases and vascular pathology.

Presbyopia treatment

There are several ways to correct visual impairment in the development of presbyopia. The easiest and most affordable way is to select glasses for reading and needlework. However, if you already wear glasses in everyday life, you will need to use several pairs of glasses, separately for distance and separately for work at close range. A more convenient option in this case would be the selection of glasses with bifocal or progressive lenses. In bifocal glasses, the lens consists of two parts, the top of the lens is for distance vision, the bottom is for reading and working at close range. In progressive glasses, the transition line between the individual parts of the lens is smoothed and the transition is smoother, which allows you to see well not only at a distance or near, but also at medium distances.

To improve vision, the modern industry offers multifocal contact lenses. The peripheral and central zones of these lenses are responsible for clear vision at different distances.

There is an option for using lenses for age-related farsightedness, called "monovision". In this case, one eye is corrected for good distance vision, and the other eye is corrected for near vision. In this situation, the brain independently chooses a clear image that a person needs at the moment. But not all patients are able to get used to this method of correcting presbyopia.