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Lecture notes, cheat sheets
Eye diseases. Myopia and astigmatism (lecture notes)
Directory / Lecture notes, cheat sheets Table of contents (expand) LECTURE No. 24. Myopia and astigmatism 1. Myopia Myopia (myopia) is one of the variants of the refractive power (clinical refraction) of the eye, which is formed simultaneously with a decrease in distance vision due to a mismatch in the position of the back main focus in relation to the central zone of the retina. Myopia is congenital (hereditary, intrauterine origin), with age it progresses and can be malignant. Acquired myopia is a type of clinical refraction. Often, with age, it increases slightly and is not accompanied by noticeable morphological changes in the eyes. This process of refractogenesis is considered as a biological option. But under certain conditions, the frequency of both congenital and acquired myopic refraction is pathological: the so-called progressive myopia is developing. Such myopia progresses in most children in the early school years, so it is often called "school", although this is not entirely correct, since myopia can progress at a more mature age. Causes of myopia Myopia usually appears in childhood, progressing with age. The following factors are of great importance in the development of myopia: 1) genetic, in which myopic parents often have myopic children. Factors such as weakness of the accommodative muscle, weakness of the connective tissue (the sclera becomes extensible, resulting in an increase in the length of the eyeball) can be inherited; 2) adverse environmental conditions, especially during prolonged work at a close distance from the eye. This is a professional, school myopia, easily developing with an incomplete development of the organism; 3) weakness of accommodation, leading to an increase in the length of the eyeball, or, on the contrary, tension of accommodation (inability of the lens to relax), which leads to spasm of accommodation. In contrast to true myopia, with false myopia, vision is restored to normal with drug treatment (i.e., seven-day instillation of a 1% atropine solution). This requires careful observation and skiascopy with the participation of an ophthalmologist. Spasm of accommodation can be eliminated with the help of special therapeutic exercises for the eyes. The initial signs of false myopia, or spasm of accommodation, a person may suspect in himself: 1) during visual work at close range, rapid eye fatigue, pain in the eyes, in the forehead, in the temples may occur; 2) near visual work can often be facilitated by using weak plus lenses (in this case, this does not mean that a person has farsightedness); 3) it may be difficult or slow to "set" the eyes to different distances, especially when looking from a close object to a distant one; 4) distance vision deteriorates. Spasm of accommodation, if left untreated, becomes persistent over time, difficult to treat and can lead to true myopia. Progressive myopia Progressive myopia is any type of myopia manifested by deterioration of distance vision. There is information about the antecedent of false myopia to true, i.e., this is a condition in which there is a more or less rapid and pronounced drop in distance visual acuity due to spasm, or tension, accommodation. However, after eliminating the spasm with the help of cycloplegic drugs (atropine, scopolamine, homatropine), vision is restored to normal, and refractometry reveals emmetropia or even farsightedness. In recent decades, myopia (myopia) more often began to develop in preschoolers who, during their upbringing, had a high visual load in combination with a sedentary lifestyle, poor nutrition and weakening of the body due to frequent illnesses (tonsillitis, dental caries, rheumatism, etc.). Among students in first and second grades, myopia occurs in 36%, in third and fourth grades in 6%, in seventh and eighth grades in 16%, in ninth and tenth grades in more than 20%. Severe (high, advanced) myopia causes over 30% of low vision and blindness from all eye diseases; it is an obstacle to the choice of many professions. The mechanism of development of myopia that occurs during childhood consists of three main links, such as: 1) visual work at close range (weak accommodation); 2) burdened heredity; 3) weakening of the sclera, violation of trophism (intraocular pressure). Consequently, according to the predominance of certain causes of development, myopia can be conditionally divided into accommodative, hereditary and scleral. The development of each of these forms of myopia over time leads to irreversible morphological changes in the eyes and a pronounced decrease in visual acuity, which often does not improve much or does not improve at all under the influence of optical correction. The main reason for this is a significant elongation of the axis of the eye: instead of 2223 mm, it reaches 3032 mm or more, which is determined using an echo-ophthalmograph. If myopia progresses within a year by less than 1,0 diopters, then it is conditionally considered benign, and if the increase is 1,0 diopters. and more malignant. However, the matter is not only in progression, but also in the size and changes in the intraocular structures (vitreous body, choroid, retina, optic nerve). A large stretching of the eyes during myopia leads to an expansion of the palpebral fissure, as a result of which a kind of bulging is created. The sclera becomes thinner, especially in the area of attachment of the lateral muscles and near the edge of the cornea. This can be determined with the naked eye by the bluish tint of the cornea due to translucence of the choroid, and sometimes by the presence of anterior staphylomas of the sclera. The cornea also stretches and thins. The anterior chamber of the eye deepens. Mild iridodonesis (trembling of the iris), destruction or liquefaction of the vitreous body may occur. Depending on the genesis and magnitude of myopia, changes in the fundus occur. It is necessary to distinguish between such changes as: 1) near-disk light reflexes; 2) myopic cones; 3) true staphylomas; 4) changes in the area of the retinal spot; 5) cystic retinal degeneration; 6) retinal detachment. Stretching of the sclera and atrophy of the pigment epithelium layer near the disc often lead to the appearance of myopic cones. Signs of a high amount of myopia are usually staphylomas, or true protrusions of the posterior sclera. In the area of the retinal spot, the most formidable changes of a degenerative and atrophic nature occur with high myopia. The formation of cracks in the choroid in the form of yellowish or whitish stripes, and then the appearance of white polymorphic, often merging foci with scattered clumps and accumulations of pigment, are the consequences of stretching the posterior segment of the eyeball. With the development of pathological changes in the area of the retinal spot, patients develop metamorphopsias (distortion of the shape and size of visible objects), weakening of vision, which eventually leads to a strong decrease, and sometimes to an almost complete loss of central vision. Progressive myopia occurs simultaneously with pathological changes in the extreme periphery of the fundus in the form of racemose retinal degeneration, and then multiple small retinal defects of slit-like, oval or round shape. Additional possibilities for the occurrence of retinal detachment explain the changes in the vitreous body. High myopia can sometimes appear in children in the first months of life, which suggests that such myopia is either hereditary or congenital. The latter develops as a result of diseases or underdevelopment in the antenatal period and is more common in children who have had a mild form of retrolental fibroplasia. Usually this myopia does not lend itself well to optical correction. Prevention and treatment of myopia. To prevent progressive myopia, the following is necessary: 1) preventing the development of myopia among the younger generation (primary prevention); 2) delay in the progression of already existing myopia (secondary prevention). The beginning of the prevention of myopia or its development should occur with the clarification of heredity and the determination of clinical refraction in children under one year old, but not later than 12 years of age. At the same time, there should be a differentiated attitude to the upbringing of the child, taking into account the state of his heredity and refraction. To do this, divide the children into two groups: 1) children with heredity aggravated by myopia, regardless of the detected size and type of refraction, with congenital myopia, with emmetropia; 2) children with farsighted refraction without heredity burdened by myopia. These are the so-called prevention groups (risk groups). Ophthalmologists must transmit lists of these groups to kindergartens and schools annually in July-August. Treatment of myopia can be conservative and surgical. Conservative treatment begins with vision correction with glasses or contact lenses. It is necessary to have the convenience of glasses and their compliance with the configuration and size of the face, ensuring visual acuity in both eyes within 0,91,0-2,03,0 and the presence of stable binocular vision. Glasses should be used constantly. In cases of moderate or high myopia, bifocal glasses can be used in such a way that the lower hemisphere of the lens is weaker than the upper one by an average of 3,0 diopters. With high myopia and anisometropia (more than XNUMX diopters), correction with hard or soft contact lenses is recommended. Treatment of rapidly progressive and severe myopia is a serious and often difficult task. The development of changes in the area of the retinal spot, the appearance of recurrent hemorrhages in the retina and vitreous body require the cessation of visual work, the creation of rest for the eyes, protection from harsh light and vigorous treatment. Both local and general treatment with calcium chloride, cysteine, preparations of Chinese magnolia vine, ginseng, mezaton, ethylmorphine hydrochloride (dionine), as well as subconjunctival oxygen injections, reflex therapy are recommended. It is necessary to prescribe rutin with ascorbic acid, riboflavin, thiamine, vitamin E, intermedin, adenosine triphosphoric acid, taufon, etc. If correction with glasses or contact lenses, conservative treatment methods, as well as reflexology do not stop or significantly reduce the rate of progression of the process, then surgical treatment is indicated. The decision on the timing and method of surgery is made depending on a number of factors. The younger the child, the faster the annual (over two to three years) progression of myopia (more than 1,0 diopters per year), the more significant the increase in the sagittal size of the eye, the greater the indications for strengthening the eye capsule with scleroplasty. The choice of scleroplasty technique is made in accordance with the stage of myopia, i.e., the location and magnitude of morphological changes. It is necessary to take into account that the less myopia, the more effective scleroplasty. Prevention of rapid progression of myopia through scleroplasty is effective in almost 90% of cases. Within two to three years after surgery, myopia often increases by 1,0 diopters. versus 3,04,0 diopters. with a conservative method of treatment. If myopia is stable for two to three years, but the child who has reached adulthood does not want to wear glasses and contact lenses or if it is impossible to ensure high visual acuity with their help, a keratotomy can be performed, i.e., non-through incisions on the cornea, due to which reduces its refractive power by a given amount. Keratotomy is most effective for low and moderate myopia, and for high myopia, keratomileusis is possible. Treatment of accommodative false myopia primarily requires limiting visual work at close range, correct correction of existing ametropia and anisometropia. The main methods of treatment are various training exercises for the ciliary muscle, instillation of drugs prescribed by an ophthalmologist, as well as reflexology. 2. Astigmatism Astigmatism is a refractive error in which different types of ametropia or different degrees of one type of ametropia are combined in one eye. Etiopathogenesis of astigmatism and its forms. The development of astigmatism is based on the unequal refraction of light rays in different meridians of the eye, which is associated with differences in the radius of curvature of the cornea (less often the lens). On the two main mutually perpendicular meridians, the strongest and weakest refractive power is observed. As a result of this feature, the image on the retina always turns out to be fuzzy, distorted. As a rule, the cause is an anomaly in the structure of the eye. However, such changes can occur after operations, eye injuries, diseases of the cornea. There is a simple astigmatism, in which emmetropia is noted in one of the main meridians, and ametropia (myopia or hypermetropia) in the other; complex astigmatism, when ametropia of the same type, but of varying degrees, is noted in both main meridians of the eye; mixed astigmatism, in which myopia is noted in one of the main meridians, and hypermetropia in the other. In astigmatic eyes, there are main meridians with the strongest and weakest refractive power. If the refractive power is the same throughout the meridian, then astigmatism is called correct, if different, incorrect. With direct astigmatism, the vertical main meridian has the strongest refraction, with the reverse horizontal. When the main meridians pass in an oblique direction, one speaks of astigmatism with oblique axes. Correct direct astigmatism with a difference in refractive power in the main meridians of 0,5 diopters. considered physiological, not causing subjective complaints. Clinical picture and diagnosis of astigmatism. Patients complain of a decrease in visual acuity, rapid eye fatigue during work, headache, and sometimes vision of objects twisted. Spherical convex and concave glasses do not improve vision. The study of refraction reveals the difference in the refractive power of the eye in different meridians. The basis of the diagnosis is to determine the refraction in the main refractive meridians. Treatment of astigmatism. Spectacles with cylindrical or spherical-cylindrical lenses (astigmatic lenses) are prescribed. The constant wearing of such glasses maintains high visual acuity and good performance. Author: Shilnikov L.V. << Back: Eye injury (Puncture wounds of the eyes. Contusions of the eye. Burns of the eyes. Frostbite of the eyes. Combat damage to the organ of vision) >> Forward: Primary glaucoma
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