Age features of central vision. Features of vision associated with age

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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 the 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 proper. 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 proper to 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 shells (a continuation of the meninges 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, as it were, is 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 lizard-like 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 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 circulatory vasculature 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, 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 fatty 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 helmets) 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.

Table 12. Age-related changes in visual acuity with normal refractive properties of the eye.
	Visual acuity (in conventional units)



6 months








adults

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.

Study protocol.
	Visual acuity for the right eye (in conventional units)	Visual acuity for the left eye (in conventional units)

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.

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 Zh. Neuropatologii i psikhiatrii. 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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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.

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 lizard-like 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 cerebral 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 circulatory vasculature 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 fatty body of the orbit decreases in size, partially atrophies, the eyeball protrudes less from the orbit.

The development of the visual analyzer begins at the 3rd week of the embryonic period.

Development of the peripheral department. Differentiation of the cellular elements of the retina occurs at the 6-10th week of intrauterine development. By the 3rd month of embryonic life, the retina includes all types of nerve elements. In a newborn, only rods function in the retina, providing black and white vision. The cones responsible for color vision are not yet mature and their number is small. And although newborns have the functions of color perception, the full inclusion of cones in work occurs only by the end of the 3rd year of life. As the cones mature, children begin to distinguish first yellow, then green, and then red (already from the age of 3 months, it was possible to develop conditioned reflexes to these colors); color recognition at an earlier age depends on the brightness, and not on the spectral characteristics of the color. Children begin to fully distinguish colors from the end of the 3rd year of life. At school age, the distinctive color sensitivity of the eye increases. The sensation of color reaches its maximum development by the age of 30 and then gradually decreases. Training is essential for developing this ability. The final morphological maturation of the retina ends by 10-12 years.

Development of additional elements of the organ of vision (prereceptor structures). In a newborn, the diameter of the eyeball is 16 mm and its weight is 3.0 g. The growth of the eyeball continues after birth. It grows most intensively during the first 5 years of life, less intensively - up to 9-12 years. In adults, the diameter of the eyeball is about 24 mm, and the weight is 8.0 g. In newborns, the shape of the eyeball is more spherical than in adults, the anteroposterior axis of the eye is shortened. As a result, in 80-94% of cases, they have far-sighted refraction. Increased extensibility and elasticity of the sclera in children contributes to slight deformation of the eyeball, which is important in the formation of refraction of the eye. So, if a child plays, draws or reads, tilting his head low, due to the pressure of the liquid on the front wall, the eyeball lengthens and myopia develops. The cornea is more convex than in adults. In the first years of life, the iris contains few pigments and has a bluish-grayish tint, and the final formation of its color is completed only by the age of 10-12. In newborns, due to the underdeveloped muscles of the iris, the pupils are narrow. Pupil diameter increases with age. At the age of 6-8 years, the pupils are wide due to the predominance of the tone of the sympathetic nerves that innervate the muscles of the iris, which increases the risk of retinal sunburn. At 8-10 years old, the pupil again becomes narrow, and by the age of 12-13, the speed and intensity of the pupillary reaction to light is the same as in an adult. In newborns and preschool children, the lens is more convex and more elastic than in an adult, and its refractive power is higher. This makes it possible to clearly see the object when it is closer to the eye than in an adult. In turn, the habit of viewing objects at a short distance can lead to the development of strabismus. The lacrimal glands and regulatory centers develop during the period from 2 to 4 months of life, and therefore tears during crying appear at the beginning of the second, and sometimes 3-4 months after birth.

The maturation of the conductive department of the visual analyzer is manifested:

1) myelination of pathways, starting at the 8-9th month of intrauterine life and ending by 3-4 years;
2) differentiation of subcortical centers.

The cortical part of the visual analyzer has the main signs of adults already in a 6-7-month-old fetus, however, the nerve cells of this part of the analyzer, like other parts of the visual analyzer, are immature. The final maturation of the visual cortex occurs by the age of 7. In functional terms, this leads to the possibility of forming associative and temporal connections in the final analysis of visual sensations. The functional maturation of the visual areas of the cerebral cortex, according to some sources, occurs already by the birth of a child, according to others - somewhat later. So, in the first months after birth, the child confuses the top and bottom of the object. If you show him a burning candle, then he, trying to grab the flame, will stretch out his hand not to the upper, but to the lower end.

Development of the functionality of the visual sensory system.

The light-perceiving function in children can be judged by the pupillary reflex, closure of the eyelids with the abduction of the eyeballs upward and other quantitative indicators of light perception, which are determined using adaptometer devices only from 4-5 years of age. The photosensitive function develops very early. Visual reflex to light (pupil constriction) - from the 6th month of intrauterine development. A protective blinking reflex to sudden light irritation is present from the first days of life. Closing of the eyelids when an object approaches the eyes appears on the 2nd-4th month of life. With age, the degree of constriction of the pupils in the light and their expansion in the dark increases (Table 14.1). Constriction of the pupils when fixing the gaze of an object occurs from the 4th week of life. Visual concentration in the form of fixation of gaze on an object with simultaneous inhibition of movements manifests itself in the 2nd week of life and lasts 1-2 minutes. The duration of this reaction increases with age. Following the development of fixation, the ability to follow a moving object with the eye and the convergence of visual axes develop. Until the 10th week of life, eye movements are uncoordinated. Eye movement coordination develops with the development of fixation, tracking, and convergence. Convergence occurs on the 2-3rd week and becomes resistant to 2-2.5 months of life. Thus, the child has a sense of light essentially from the moment of birth, but a clear visual perception in the form of visual samples is not available to him, since although the retina is developed at the time of birth, the fovea has not completed its development, the final differentiation of cones ends by the end of the year, and subcortical and cortical centers in newborns are morphologically and functionally immature. These features determine the lack of object vision and perception of space up to 3 months of life. Only from this time on, the child's behavior begins to be determined by visual afferentation: before feeding, he visually finds his mother's breast, examines his hands, and grasps toys located at a distance. The development of object vision is also associated with the perfection of visual acuity, eye motility, with the formation of complex interanalyzer connections when visual sensations are combined with tactile and proprioceptive ones. The difference in the shapes of objects appears on the 5th month.

Changes in the quantitative indicators of light perception in the form of a threshold of light sensitivity of the dark-adapted eye in children compared with adults are presented in Table. 14.2. Measurements have shown that the sensitivity to light of a dark-adapted eye sharply increases up to 20 years, and then gradually decreases. Due to the great elasticity of the lens, the eyes of children are more capable of accommodation than those of adults. With age, the lens gradually loses its elasticity and its refractive properties deteriorate, the volume of accommodation decreases (i.e., it reduces the increase in the refractive power of the lens when it is convex), the point of proximal vision is removed (Table 14.3).

Table 14.1

Age-related changes in the diameter and reactions of pupillary constriction to light

Table 14.2

Light sensitivity of the dark-adapted eye of people of different ages

Table 14.3

Change in the volume of accommodation with age

Color perception in children is manifested from the moment of birth, however, for different colors, it, apparently, is not the same. According to the results of the electroretinogram (ERG), the functioning of cones to orange light was established in children from 6 hours of life after birth. There is evidence that in the last weeks of embryonic development, the cone apparatus is able to respond to red and green colors. It is assumed that from the moment of birth to 6 months of age, the order of perception of color discrimination is as follows: yellow, white, pink, red, brown, black, blue, green, violet. At 6 months, children distinguish all colors, but correctly name them only from 3 years.

Visual acuity increases with age and in 80-94% of children and adolescents it is greater than in adults. For comparison, we present data on visual acuity (in arbitrary units) in children of different ages (Table 14.4).

Table 14.4

Visual acuity in children of different ages

Due to the spherical shape of the eyeball, short anteroposterior axis, large convexity of the cornea and lens in newborns, the refraction value is 1-3 diopters. In preschoolers and schoolchildren, farsightedness (if any) is due to the flat shape of the lens. Children in preschool and school may develop myopia when reading for a long time in a sitting position with a large tilt of the head and with accommodation tension that occurs in poor lighting while reading or looking at small objects. These conditions lead to an increase in blood supply to the eye, an increase in intraocular pressure and a change in the shape of the eyeball, which is the cause of myopia.

With age, stereoscopic vision also improves. It begins to form from the 5th month of life. This is facilitated by improving the coordination of eye movement, fixing the gaze on the object, improving visual acuity, and the interaction of the visual analyzer with others (especially with the tactile one). By the 6-9th month, an idea arises of the depth and remoteness of the location of objects. Stereoscopic vision reaches its optimal level by the age of 17-22, and from the age of 6, girls have a higher stereoscopic visual acuity than boys.

The field of vision is formed by the 5th month. Until this time, children fail to evoke a defensive blinking reflex when an object is introduced from the periphery. With age, the field of view increases, especially intensively from 6 to 7.5 years. By the age of 7, its size is approximately 80% of the size of the field of view of an adult. In the development of the visual field, sexual characteristics are observed. The expansion of the field of vision continues up to 20-30 years. The field of view determines the amount of educational information perceived by the child, i.e. throughput of the visual analyzer, and, consequently, learning opportunities. In the process of ontogenesis, the bandwidth of the visual analyzer (bps) also changes and reaches the following values in different age periods (Table 14.5).

Table 14.5

Bandwidth of the visual analyzer, bit/s

Sensory and motor functions of vision develop simultaneously. In the first days after birth, eye movements are asynchronous, with the immobility of one eye, you can observe the movement of the other. The ability to fix an object with a glance, or, figuratively speaking, a "fine tuning mechanism", is formed at the age of 5 days to 3-5 months. A reaction to the shape of an object is noted already in a 5-month-old child. In preschoolers, the first reaction is the shape of the object, then its size, and lastly, the color.

At 7-8 years old, the eye in children is much better than in preschoolers, but worse than in adults; has no gender differences. In the future, in boys, the linear eye becomes better than in girls.

The functional mobility (lability) of the receptor and cortical parts of the visual analyzer is the lower, the younger the child.

Violations and correction of vision. The high plasticity of the nervous system, which makes it possible to compensate for the missing functions at the expense of the remaining ones, is of great importance in the process of teaching and educating children with sensory organ defects. It is known that deaf-blind children have increased sensitivity of tactile, gustatory and olfactory analyzers. With the help of the sense of smell, they can navigate the area well and recognize relatives and friends. The more pronounced the degree of damage to the child's sense organs, the more difficult the educational work with him becomes. The vast majority of all information from the outside world (about 90%) enters our brain through the visual and auditory channels, therefore, the organs of vision and hearing are of particular importance for the normal physical and mental development of children and adolescents.

Among visual defects, the most common are various forms of refractive error of the optical system of the eye or a violation of the normal length of the eyeball. As a result, the rays coming from the object are not refracted on the retina. With a weak refraction of the eye due to a violation of the functions of the lens - its flattening, or with a shortening of the eyeball, the image of the object is behind the retina. People with such visual impairments have trouble seeing close objects; such a defect is called farsightedness (Fig. 14.4.).

When the physical refraction of the eye is increased, for example, due to an increase in the curvature of the lens, or an elongation of the eyeball, the image of the object is focused in front of the retina, which disrupts the perception of distant objects. This visual defect is called myopia (see Fig. 14.4.).

Rice. 14.4. Refraction scheme: in the far-sighted (a), normal (b) and myopic (c) eye

With the development of myopia, the student does not see well what is written on the blackboard, and asks to be transferred to the first desks. When reading, he brings the book closer to his eyes, bows his head strongly while writing, in the cinema or in the theater he tends to take a seat closer to the screen or stage. When examining an object, the child squints his eyes. To make the image on the retina clearer, it brings the object in question too close to the eyes, which causes a significant load on the muscular apparatus of the eye. Often the muscles do not cope with such work, and one eye deviates towards the temple - strabismus occurs. Myopia can develop with diseases such as rickets, tuberculosis, rheumatism.

A partial violation of color vision is called color blindness (after the English chemist Dalton, who first discovered this defect). Color blind people usually do not distinguish between red and green colors (they seem to them to be gray in different shades). About 4-5% of all men are color blind. In women, it is less common (up to 0.5%). To detect color blindness, special color tables are used.

Prevention of visual impairment is based on the creation of optimal conditions for the functioning of the organ of vision. Visual fatigue leads to a sharp decrease in the performance of children, which affects their general condition. Timely change of activities, changes in the environment in which training sessions are held, contribute to the increase in working capacity.

Of great importance is the correct mode of work and rest, school furniture that meets the physiological characteristics of students, sufficient lighting of the workplace, etc. While reading, every 40-60 minutes you need to take a break for 10-15 minutes to give your eyes a rest; to relieve the tension of the accommodation apparatus, children are advised to look into the distance.

In addition, an important role in the protection of vision and its function belongs to the protective apparatus of the eye (eyelids, eyelashes), which require careful care, compliance with hygiene requirements and timely treatment. Improper use of cosmetics can lead to conjunctivitis, blepharitis and other diseases of the organs of vision.

Particular attention should be paid to the organization of work with computers, as well as watching television. If visual impairment is suspected, an ophthalmologist should be consulted.

Up to 5 years, hypermetropia (farsightedness) predominates in children. With this defect, glasses with collective biconvex glasses help (giving the rays passing through them a converging direction), which improve visual acuity and reduce excessive accommodation stress.

In the future, due to the load during training, the frequency of hypermetropia decreases, and the frequency of emmetropia (normal refraction) and myopia (nearsightedness) increases. By the end of school, compared with the primary grades, the prevalence of myopia increases by 5 times.

The formation and progression of myopia contributes to the lack of light. Visual acuity and stability of clear vision in students are significantly reduced by the end of the lessons, and this decrease is the sharper, the lower the level of illumination. With an increase in the level of illumination in children and adolescents, the speed of distinguishing visual stimuli increases, the speed of reading increases, and the quality of work improves. With workplace illumination of 400 lux, 74% of the work was performed without errors, with illumination of 100 lux and 50 lux, respectively, 47 and 37%.

With good lighting in normally hearing children, adolescents have an aggravated hearing acuity, which also favors working capacity and has a positive effect on the quality of work. So, if the dictations were conducted at an illumination level of 150 lux, the number of omitted or misspelled words was 47% less than in similar dictations conducted at an illumination level of 35 lux.

The development of myopia is influenced by the study load, which is directly related to the need to consider objects at close range, its duration during the day.

You should also know that in students who are little or not at all in the air around noon, when the intensity of ultraviolet radiation is maximum, phosphorus-calcium metabolism is disturbed. This leads to a decrease in the tone of the eye muscles, which, with high visual load and insufficient illumination, contributes to the development of myopia and its progression.

Myopic children are considered to be those whose myopic refraction is 3.25 diopters and above, and corrected visual acuity is 0.5-0.9. Such students are recommended physical education classes only according to a special program. They are also contraindicated in heavy physical work, prolonged stay in a bent position with their heads bowed.

With myopia, glasses with scattering biconcave glasses are prescribed, which turn parallel rays into divergent ones. Myopia in most cases is congenital, but it can increase at school age from elementary to senior grades. In severe cases, myopia is accompanied by changes in the retina, which leads to a decrease in vision and even retinal detachment. Therefore, children suffering from myopia must strictly follow the instructions of the ophthalmologist. Timely wearing of glasses by schoolchildren is mandatory.

In the development of the visual analyzer after birth, 5 periods are distinguished:

the formation of the area of the macula and the central fovea of the retina during the first half of life - out of 10 layers of the retina, mainly 4 remain (visual cells, their nuclei and boundary membranes);
increase in the functional mobility of the visual pathways and their formation during the first six months of life
improvement of the visual cellular elements of the cortex and cortical visual centers during the first 2 years of life;
formation and strengthening of connections of the visual analyzer with other organs during the first years of life;
morphological and functional development of cranial nerves in the first 2-4 months of life.

The formation of the visual functions of the child occurs in accordance with these stages of development.

Anatomical features

Eyelid skin in newborns, it is very tender, thin, smooth, without folds, the vascular network shines through it. The palpebral fissure is narrow and corresponds to the size of the pupil. The child blinks 7 times less than adults (2-3 blinks per minute). During sleep, there is often no complete closure of the eyelids and a bluish strip of sclera is visible. By 3 months after birth, the mobility of the eyelids increases, the child blinks 3-4 times per minute, by 6 months - 4-5, and by 1 year - 5-6 times per minute. By the age of 2, the palpebral fissure increases, acquires an oval shape as a result of the final formation of the muscles of the eyelids and an increase in the eyeball. The child blinks 7-8 times per minute. By the age of 7-10, the eyelids and palpebral fissure correspond to those of adults, the child blinks 8-12 times per minute.

Lacrimal gland begins to function only 4-6 weeks or more after birth, children at this time cry without tears. However, the lacrimal accessory glands in the eyelids immediately produce tears, which is well defined by a pronounced lacrimal stream along the edge of the lower eyelid. The absence of a lacrimal stream is regarded as a deviation from the norm and may be the cause of the development of dacryocystitis. By 2-3 months of age, the normal functioning of the lacrimal gland and lacrimation begins. At the birth of a child, the lacrimal ducts in most cases are already formed and passable. However, in about 5% of children, the lower opening of the lacrimal canal opens later or does not open at all, which may cause the development of dacryocystitis in the newborn.

eye socket(orbit) in children under 1 year old is relatively small, so it gives the impression of large eyes. In shape, the orbit of newborns resembles a trihedral pyramid, the bases of the pyramids have a convergent direction. The bone walls, especially the medial one, are very thin and contribute to the development of collateral edema of the eye tissue (cellulitis). The horizontal size of the eye sockets of a newborn is larger than the vertical one, the depth and convergence of the axes of the eye sockets is less, which sometimes creates the impression of convergent strabismus. The size of the eye sockets is about 2/3 of the corresponding size of the eye sockets of an adult. The eye sockets of a newborn are flatter and smaller, therefore they protect the eyeballs from injury less well and give the impression of standing eyeballs. The palpebral fissures in children are wider due to insufficient development of the temporal wings of the sphenoid bones. The rudiments of the teeth are located closer to the contents of the orbit, which facilitates the entry of an odontogenic infection into it. The formation of the orbit ends by the age of 7, by 8-10 years the anatomy of the orbit approaches that of adults.

Conjunctiva the newborn is thin, tender, not moist enough, with reduced sensitivity, can be easily injured. By the age of 3 months, it becomes more moist, shiny, sensitive. Pronounced moisture and pattern of the conjunctiva may be a sign of inflammatory diseases (conjunctivitis, dacryocystitis, keratitis, uveitis) or congenital glaucoma.

Cornea newborns is transparent, but in some cases in the first days after birth it is somewhat dull and, as it were, opalescent. Within 1 week, these changes disappear without a trace, the cornea becomes transparent. This opalescence should be distinguished from corneal edema in congenital glaucoma, which is relieved by the installation of a hypertonic solution (5%) of glucose. Physiological opalescence does not disappear when these solutions are instilled. It is very important to measure the diameter of the cornea, since its increase is one of the signs of glaucoma in children. The diameter of the cornea of a newborn is 9-9.5 mm, by 1 year it increases by 1 mm, by 2-3 years - by another 1 mm, by 5 years it reaches the diameter of the cornea of an adult - 11.5 mm. In children under 3 months of age, the sensitivity of the cornea is sharply reduced. The weakening of the corneal reflex leads to the fact that the child does not respond to the ingress of foreign bodies into the eye. Frequent eye examinations in children of this age are important for the prevention of keratitis.

Sclera the newborn is thin, with a bluish tinge, which gradually disappears by the age of 3 years. This sign should be carefully considered, since blue sclera can be a sign of diseases and stretching of the sclera with increased intraocular pressure in congenital glaucoma.

Front camera in newborns it is small (1.5 mm), the angle of the anterior chamber is very sharp, the root of the iris has a slate color. It is believed that this color is due to the remnants of embryonic tissue, which is completely absorbed by 6-12 months. The angle of the anterior chamber gradually opens up and by the age of 7 becomes the same as in adults.

iris in newborns it is bluish-gray in color due to the small amount of pigment, by the age of 1 it begins to acquire an individual color. The color of the iris is finally established by 10-12 years of age. Direct and friendly pupillary reactions in newborns are not very pronounced, the pupils are poorly dilated by medications. By the age of 1 year, the pupil reaction becomes the same as in adults.

ciliary body in the first 6 months is in a spastic state, which causes myopic clinical refraction without cycloplegia and a sharp change in refraction towards hyperopic after installations of a 1% solution of homatropin.

Ocular fundus newborns are pale pink in color, with more or less pronounced parquet and a lot of light reflections. It is less pigmented than in an adult, the vasculature is clearly visible, retinal pigmentation is often finely punctate or spotted. On the periphery, the retina is grayish in color, the peripheral vascular network is immature. In newborns, the optic nerve head is pale, with a bluish-gray tint, which can be mistaken for its atrophy. Reflexes around the macula are absent and appear during the 1st year of life. During the first 4-6 months of life, the fundus becomes almost identical to the fundus of an adult, by the age of 3 there is a reddening of the tone of the fundus. In the optic disc, the vascular funnel is not determined, it begins to form by the age of 1 and ends by the age of 7.

Functional features

A feature of the activity of the nervous system of the child after birth is the predominance of subcortical formations. The brain of the newborn is still underdeveloped, the differentiation of the cortex and pyramidal pathways is not completed. As a result, newborns have a tendency to diffuse reactions, to their generalization and irradiation, and such reflexes are caused, which in adults occur only in pathology.

The specified ability of the central nervous system of the newborn has a significant impact on the activity of sensory systems, in particular visual. With a sharp and sudden illumination of the eyes, generalized protective reflexes may occur - a shudder of the body and the Peiper phenomenon, which is expressed in the narrowing of the pupil, the closing of the eyelids and the strong tilting of the child's head back. The main reflexes also appear when other receptors are stimulated, in particular the tactile one. So, with intensive scratching of the skin, the pupils dilate, with a light tapping on the nose, the eyelids close. There is also the phenomenon of "doll eyes", in which the eyeballs move in the opposite direction to the passive movement of the head.

In conditions of illumination of the eyes with bright light, a blinking reflex and abduction of the eyeballs upward occur. Such a protective reaction of the organ of vision to the action of a specific stimulus is obviously due to the fact that the visual system is the only one of all sensory systems that is affected by adequate afferentation only after the birth of a child. It takes some getting used to the light.

As is known, other afferentations - auditory, tactile, interoceptive and proprioceptive - exert their influence on the corresponding analyzers even in the period of intrauterine development. However, it should be emphasized that in postnatal ontogenesis the visual system develops at an accelerated pace, and visual orientation soon outstrips auditory and tactile-proprioceptive ones.

Already at the birth of a child, a number of unconditioned visual reflexes are noted - a direct and friendly reaction of the pupils to light, a short-term orienting reflex of turning both eyes and head to a light source, an attempt to track a moving object. However, the expansion of the pupil in the dark is slower than its narrowing in the light. This is explained by the underdevelopment at an early age of the iris dilator or the nerve innervating this muscle.

On the 2-3rd week, as a result of the appearance of conditioned reflex connections, the complication of the activity of the visual system begins, the formation and improvement of the functions of object, color and spatial vision.

Thus, light sensitivity appears immediately after birth. True, under the action of light, even an elementary visual image does not arise in a newborn, and mainly inadequate general and local defensive reactions are caused. At the same time, from the very first days of a child's life, light has a stimulating effect on the development of the visual system as a whole and serves as the basis for the formation of all its functions.

With the help of objective methods of recording changes in the pupil, as well as other visible reactions (for example, the Peiper reflex) to light of different intensity, it was possible to get some idea of the level of light perception in young children. The sensitivity of the eye to light, measured by the pupillomotor reaction of the pupil with the help of a pupilloscope, increases in the first months of life and reaches the same level as in an adult at school age.

Absolute Light Sensitivity in newborns it is sharply reduced, and under conditions of dark adaptation it is 100 times higher than during adaptation to light. By the end of the first six months of a child's life, light sensitivity increases significantly and corresponds to 2/3 of its level in an adult. In the study of visual dark adaptation in children aged 4-14, it was found that with age, the level of the adaptation curve increases and becomes almost normal by the age of 12-14.

Reduced light sensitivity in newborns is explained by the insufficient development of the visual system, in particular the retina, which is indirectly confirmed by the results of electroretinography. In young children, the shape of the electroretinogram is close to normal, but its amplitude is reduced. The latter depends on the intensity of the light falling on the eye: the more intense the light, the greater the amplitude of the electroretinogram.

J. Francois and A. de Rouk (1963) found that wave a in the first months of a child's life is below normal and reaches its normal value after 2 years.

Photopic wave b 1 develops even more slowly and at the age of over 2 years still has a low value.
Scotopic wave b 2 with weak stimuli in children from 2 to 6 years is significantly lower than in adults.
The curves of the a and b waves in dual pulses are quite different from those seen in adults.
The refractory period is shorter at the beginning.

Shaped central vision appears in a child only on the 2nd month of life. In the future, its gradual improvement takes place - from the ability to detect an object to the ability to distinguish and recognize it. The ability to distinguish the simplest configurations is provided by the appropriate level of development of the visual system, while the recognition of complex images is associated with the intellectualization of the visual process and requires training in the psychological sense of the word.

By studying the child's reaction to the presentation of objects of different sizes and shapes (the ability to differentiate them during the development of conditioned reflexes, as well as the reaction of optokinetic nystagmus, it was possible to obtain information about uniform vision in children even at an early age. Thus, it was found that

at the 2-3rd month notices the mother's breasts,
at the 4-6th month of life, the child reacts to the appearance of persons serving him,
at the 7-10th month, the child develops the ability to recognize geometric shapes (cube, pyramid, cone, ball), and
on the 2-3rd year of life, painted images of objects.

Perfect perception of the shape of objects and normal visual acuity develop in children only during the period of schooling.

In parallel with the development of shaped vision, the formation color vision , which is also primarily a function of the retinal cone apparatus. With the help of a conditioned reflex technique, it was found that the ability to differentiate color first appears in a child at the age of 2-6 months. It is noted that color discrimination begins primarily with the perception of red, while the ability to recognize colors of the short-wavelength part of the spectrum (green, blue) appears later. This is obviously due to the earlier formation of red receivers compared to receivers of other colors.

By the age of 4-5, color vision in children is already well developed, but continues to improve in the future. Anomalies of color perception in them occur with approximately the same frequency and in the same quantitative ratios between males and females as in adults.

Field of vision boundaries in preschool children by about 10% narrower than in adults. At school age, they reach normal values. The dimensions of the blind spot vertically and horizontally, determined by a campimetric study from a distance of 1 m, are on average 2-3 cm larger in children than in adults.

For the emergence binocular vision a functional relationship is necessary between both halves of the visual analyzer, as well as between the optical and motor apparatus of the eyes. Binocular vision develops later than other visual functions.

It is hardly possible to speak about the presence of true binocular vision, i.e., the ability to merge two monocular images into a single visual image, in infants. They have only the mechanism of binocular fixation of the object as the basis for the development of binocular vision.

In order to objectively judge the dynamics of the development of binocular vision in children, you can use a test with a prism. The adjusting movement that occurs during this test indicates that there is one of the main components of the combined activity of both eyes - fusion reflex. L.P. Khukhrina (1970), using this technique, found that 30% of children in the first year of life have the ability to move an image shifted in one of the eyes to the central fovea of the retina. The frequency of the phenomenon increases with age and reaches 94.1% in the 4th year of life. In the study using a color device, binocular vision at the 3rd and 4th years of life was detected in 56.6 and 86.6% of children, respectively.

The main feature of binocular vision is, as is known, a more accurate assessment of the third spatial dimension - the depth of space. The average threshold value of binocular deep vision in children aged 4-10 years is gradually decreasing. Consequently, as children grow and develop, the estimation of the spatial dimension becomes more and more accurate.

The following main stages in the development of spatial vision in children can be distinguished. At birth, a child does not have conscious vision. Under the influence of bright light, his pupil constricts, his eyelids close, his head jerkily leans back, but his eyes wander aimlessly independently of each other.

2-5 weeks after birth, strong illumination already encourages the child to keep his eyes relatively still and stare at the light surface. The effect of light is especially noticeable if: it hits the center of the retina, which by this time has developed into a highly valuable area that allows you to get the most detailed and vivid impressions. By the end of the first month of life, optical stimulation of the periphery of the retina causes a reflex movement of the eye, as a result of which the light object is perceived by the center of the retina.

This central fixation at first takes place fleetingly and only on one side, but gradually, due to repetition, it becomes stable and bilateral. The aimless wandering of each eye is replaced by the coordinated movement of both eyes. Arise convergent and tied to them fusional movement, the physiological basis of binocular vision is formed - the optomotor mechanism of bifixation. During this period, the average visual acuity in a child (measured by optokinetic nystagmus) is approximately 0.1, by the age of 2 it rises to 0.2-0.3 and only by 6-7 years reaches 0.8-1.0.

Thus, (the binocular visual system is formed, despite the still obvious inferiority of the monocular visual systems, and is ahead of their development. This happens, obviously, in order to ensure, first of all, spatial perception, which to the greatest extent contributes to the perfect adaptation of the organism to the conditions of external By the time high foveal vision makes more and more stringent demands on the apparatus of binocular vision, it is already quite developed.

During the 2nd month of life, the child begins to master the near space. This involves visual, proprioceptive and tactile stimuli that mutually control and complement each other. At first, close objects are seen in two dimensions (height and width), but thanks to the sense of touch they are perceptible in three dimensions (height, width and depth). This is how the first ideas about the corporeality (volume) of objects are invested.

At the 4th month, children develop a grasping reflex. At the same time, most children determine the direction of objects correctly, but the distance is estimated incorrectly. The child also makes mistakes in determining the volume of objects, which is also based on an estimate of distance: he tries to grasp the incorporeal sun spots on the blanket and moving shadows.

From the second half of life, the development of distant space begins. The sense of touch is replaced by crawling and walking. They allow you to compare the distance over which the body moves with changes in the size of the images on the retina and the tone of the oculomotor muscles: visual representations of the distance are produced. Therefore, this function develops later than others. It provides a three-dimensional perception of space and is compatible only with complete coordination of the movements of the eyeballs and symmetry in their position.

It should be borne in mind that the mechanism of orientation in space goes beyond the scope of the visual system and is the product of a complex synthetic activity of the brain. In this regard, the further improvement of this mechanism is closely connected with the cognitive activity of the child. Any significant change in the environment, perceived by the visual system, serves as the basis for constructing sensorimotor actions, for acquiring knowledge about the relationship between an action and its result. The ability to remember the consequences of one's actions, in fact, is the process of learning in the psychological sense of the word.

Significant qualitative changes in spatial perception occur at the age of 2-7 years, when the child masters speech and develops abstract thinking. The visual assessment of space is improved at an older age.

In conclusion, it should be noted that the development of visual sensations involves both innate mechanisms developed and fixed in phylogeny, and mechanisms acquired in the process of accumulating life experience. In this regard, the long-standing dispute between supporters of nativism and empiricism about the leading role of one of these mechanisms in the formation of spatial perception seems pointless.

Features of the optical system and refraction

The eye of a newborn has a significantly shorter anteroposterior axis (approximately 17-18 mm) and a higher refractive power (80.0-90.9 diopters) than the eye of an adult. The differences in the refractive power of the lens are especially significant: 43.0 diopters in children and 20.0 diopters in adults. The refractive power of the cornea of the eye of a newborn is on average 48.0 diopters, an adult - 42.5 diopters.

The eye of a newborn, as a rule, has a hyperopic refraction. Its degree is on average 2.0-4.0 diopters. In the first 3 years of a child's life, intensive growth of the eye occurs, as well as flattening of the cornea and especially the lens. By the 3rd year, the length of the anteroposterior axis of the eye reaches 23 mm, i.e., it is approximately 95% of the size of the adult eye. The growth of the eyeball continues up to 14-15 years. By this age, the length of the axis of the eye reaches an average of 24 mm, the refractive power of the cornea is 43.0 diopters, and the lens is 20.0 diopters.

As the eye grows, the variability of its clinical refraction decreases. The refraction of the eye slowly increases, i.e., it shifts towards emmetropic.

There are good reasons to believe that the growth of the eye and its parts during this period is a self-regulating process, subject to a specific goal - the formation of a weak hyperopic or emmetropic refraction. This is evidenced by the presence of a high inverse correlation (from -0.56 to -0.80) between the length of the anteroposterior axis of the eye and its refractive power.

Static refraction continues to slowly change throughout life. In the general trend towards a change in the average refraction value (starting from birth and ending at the age of 70 years), two phases of hypermetropization of the eye, weakening (refraction) can be distinguished - in early childhood and in the period from 30 to 60 years, and two stages of myopization of the eye (intensification of refraction) aged 10 to 30 years and after 60 years. It should be borne in mind that the opinion about the weakening of refraction in early childhood and its strengthening after 60 years is not shared by all researchers.

With increasing age, the dynamic refraction of the eye also changes. Three age periods deserve special attention.

The first - from birth to 5 years - is characterized primarily by the instability of the indicators of dynamic refraction of the eye. During this period, the accommodation response to visual requests and the tendency of the ciliary muscle to spasm are not quite adequate. Refraction in the zone of further vision is labile and easily shifts to the side of myopia. Congenital pathological conditions (congenital myopia, nystagmus, etc.), in which the activity of the dynamic refraction of the eye decreases, can delay its normal development. The tone of accommodation usually reaches 5.0-6.0 diopters or more, mainly due to hypermetropic refraction, characteristic of this age period. In violation of binocular vision and binocular interaction of dynamic refraction systems, various types of eye pathology can develop, primarily strabismus. The ciliary muscle is not efficient enough and is not yet ready for active visual work at close range.
The other two periods are, apparently, critical age periods of increased vulnerability of dynamic refraction: the age of 8-14 years, at which the formation of the dynamic refraction system of the eye is especially active, and the age of 40-50 years and more, when this system undergoes involution. In the age period of 8-14 years, static refraction approaches emmetropia, as a result of which optimal conditions are created for the activity of the dynamic refraction of the eye. At the same time, this is a period when general body disorders and adynamia can have an adverse effect on the ciliary muscle, contributing to its weakening, and the visual load increases significantly. The consequence of this is a tendency to a spastic state of the ciliary muscle and the occurrence of myopia. The increased growth of the body during this prepubertal period contributes to the progression of myopia.

Of the features of the dynamic refraction of the eye in persons 40-50 years of age and older, changes should be distinguished that are natural manifestations of the age-related involution of the eye, and changes associated with the pathology of the organ of vision and general diseases of the elderly and senile age. Typical manifestations of the physiological aging of the eye include presbyopsia, which is mainly due to a decrease in the elasticity of the lens, a decrease in the volume of accommodation, a slow weakening of refraction, a decrease in the degree of myopia, the transition of edimetropic refraction to farsightedness, an increase in the degree of farsightedness, an increase in the relative frequency of astigmatism of the reverse type, more rapid eye fatigue due to decrease in adaptive capacity. Of the conditions associated with age-related pathology of the eye, changes in refraction with the onset of clouding of the lens come to the fore. Of the common diseases that have the greatest effect on dynamic refraction, one should single out diabetes mellitus, in which the optical settings of the eye are characterized by great lability.

The human eyeball develops from several sources. The photosensitive membrane (retina) comes from the side wall of the cerebral bladder (the future diencephalon), the lens - from the ectoderm, the vascular and fibrous membranes - 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 bubbles. 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). 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 is formed 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, 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.
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, its 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 to the 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, fatty
the 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.
Questions for repetition and self-control:

List the sense organs, give each of them a functional description.
Describe the structure of the membranes of the eyeball.
Name the structures related to the transparent media of the eye.
List the organs that belong to the auxiliary apparatus of the eye. What are the functions of each of the auxiliary organs of the eye?
Describe the structure and functions of the accommodative apparatus of the eye.
Describe the pathway of the visual analyzer from the receptors that perceive light to the cerebral cortex.
Describe the adaptation of the eye to light and color vision.