SHORT-SIGHTEDNESS

From Big Medical Encyclopedia

SHORT-SIGHTEDNESS (synonym myopia) — one of types of anomalies of a refraction of an eye, at Krom the parallel rays of light getting into an eye after refraction agree in focus not on a retina, and ahead of it. The concept «short-sightedness» is caused by the fact that at this anomaly the considered subject is well visible only at a short distance. Other name B. — a myopia (grech, I close myo, I blink eyes) — is connected with the fact that persons with such anomaly better to see the remote objects, blink eyes. It promotes obtaining clearer images on a retina.

the Path of rays in a miopichesky eye: 1 — parallel beams (proceed from far located objects) are focused ahead of a retina; 2 — the dispersing beams (proceed from close located objects) are focused on a retina.

At a normal, proportional emmetropichesky refraction (see. Emmetropias ) the parallel rays of light getting into an eye after refraction agree in focus on a mesh cover; at B. of it does not occur. Parallel beams after refraction in a short-sighted eye connect in focus — in any point ahead of a mesh cover (fig., 2); therefore, the main back focal length is rather shorter than length of an eyeglobe here. It can depend or on the fact that the refracting system of an eye turns out rather strong (so-called refraction B.), or that the longitudinal (front-back) axis of an eye is excessively big in comparison with its refracting force (so-called axial B.). Refraction B. is practically not of great importance, in clinic it is necessary to deal hl. obr. with axial B.

According to some authors (E. Zh. Tron), the considerable number of cases of B. should be carried to so-called combinational B., at a cut and length of an axis of an eye, and the refracting force do not exceed the sizes which are found at an emmetropia. But both of these factors are combined in such a way that B. as a result turns out; at the same time it is necessary to specify that cases with rather low degree of this type of anomaly of a refraction belong to combinational B. usually.

If the parallel beams proceeding from infinitely far objects refract in a short-sighted eye in such a way that their focus appears ahead from a retina, then in process of approach of a subject to an eye beams will gradually accept more and more dispersing direction, and focus after their refraction in such eye will approach more and more a retina. At last, at the known provision of a subject rate of divergence of the beams going from it will turn out such that focus will just get on a retina (fig., 2), at the same time on a retina the clear, sharp image of a subject is for the first time formed. It is further point of clear sight (see). Sees all objects lying further this point, a short-sighted eye in circles of light scattering, i.e. it is not clear. The provision of this point defines so-called degree of B., to-ruyu it is accepted to express in dioptries. If the further point of clear sight is at distance 1.i before an eye, then it will correspond to B. in 1,0 dptr. At the provision of this point at distance of 50 cm from B.'s eye will equal 2,0 dptr, at distance of 25 cm — 4,0 dptr etc. Thus, the B.'s degree is higher, the distance is shorter, in limits to-rogo a short-sighted eye it is capable to see clearly.

At approach of a subject the beams proceeding from a subject are closer than a further point of clear sight of this eye to an eye accept such rate of divergence, at a cut they would have to meet only behind a retina. Actually it does not happen since there is an inclusion of accommodation and beams stronger refract and come down on a retina. The point, closest to an eye, beams from a cut still can agree in focus on a retina and edges can be clear to the accommodation seen at the maximum tension, carries the name the closest point of clear sight (see). The distance between further and next points of clear sight is that distance, in limits to-rogo a short-sighted eye can well see. In most cases this distance is small and the hl depends. obr. from B.'s degree (the B. is higher, the this distance is shorter), and also at most accommodations. The last factor, however, practically almost does not play a role at B. in 3,0 — 4,0 dptr as the further point of clear sight of such eyes lies at distance of 33 — 25 cm before an eye, i.e. is from an eye on a usual, average, most convenient working distance, and for an eye there is no need to strengthen in this case the refraction by inclusion of accommodation.

In order that a short-sighted eye could see clearly the remote objects from which go parallel (or close to them) beams, it is necessary to make these beams dispersing. It can be reached by use of the corresponding dispersing lenses. The lens giving rate of divergence of parallel beams of edge corresponds to their discrepancy from a further point of clear sight of this eye, and defines degree it B. Such lens has the focal length equal to an otstoyaniye from an eye of a further point of clear sight. Thus, on the one hand, B.'s degree is determined by the provision of a further point of clear sight, and on the other hand, by the refracting force of a lens, corrective B., it is possible to judge the provision of a further point of clear sight of this eye. The refracting force of a lens (in dioptries) shows as far as it is necessary to weaken a refraction of a short-sighted eye. These dispersing lenses are applied to correction (correction) of short-sightedness.

As under the terms of the sight short-sighted people are usually forced to hold the considered subject close to eyes, eyes at the same time strongly converge (see. Convergence of eyes ). Due to the existence fiziol, bonds between convergence and accommodation of an eye (see) at short-sighted the special condition of involuntary steady excessive stress of accommodation (a so-called spasm of accommodation) can sometimes be observed that even more strengthens a refractivity of an eye, i.e. does it as if to even more short-sighted, than it is (pseudo-myopia). At strong long convergence increases on a gruzk on internal direct muscles of eyes; this circumstance can lead to the phenomena of exhaustion, the muscular fatigue (a so-called muscular asthenopia) which is followed by feeling of an ache in eyes, pains in eye-sockets, a headache. In this case it is necessary to interrupt the work connected with tension of accommodation. The phenomena of a muscular asthenopia disappear if to close one eye since during the use only of one eye convergence disappears.

Because short-sighted shall converge strongly, but do not need accommodation, relationship between these two functions is broken fiziol. The muscular konvergentsionny device which is not supported by a necessary impulse from accommodation and forced to work, besides, strenuously is exhausted, solid vision falls apart at first only temporarily, and then is long and resistant. Monocular sight therefore the eye excluded from the act of binocular fixing deviates knaruzh is established, i.e. the concomitant dispersing strabismus develops.

Visual acuity afar at short-sighted always happens below norm, however by means of the corresponding dispersing lenses, corrective B., visual acuity can be improved considerably, especially at weak and average degrees B. At higher degree of B. (higher than 6,0 dptr) visual acuity as a result of correction by lenses nevertheless remains below norm, and at B. higher than 10,0 dptr it is almost impossible to achieve correction of normal visual acuity. It is connected with the changes of an eyeground which are the most expressed at high B.

the Aetiology

On an origin and the reasons of development of B. many contradictory opinions were expressed. As a starting point at creation of various theories of B. a number of strongly established facts served. First of all the fact that children are born almost always far-sighted belongs to their number. The inborn B. stated from the first days of life, the phenomenon very rare. In an enormous most cases of B. begins to develop in school days — in elementary grades of short-sighted children less and degree of river at them is lower, than at children of the senior classes. It is more short-sighted people in those productions and workshops where it is necessary it is long to carry out hard work at a short distance from eyes. All these indisputable facts were the basis for creation of the theory of «school B.», or the «worker B.» recognizing as a proximate cause of development of B. work at distance, close from eyes. A number of authors put forward a factor of heredity as the main reason for development of B. Supporters of the hereditary theory of an origin of B. (M. N. Averbakh, etc.) referred to the fact that in the same family (in the same conditions) at one children B. develops, and others do not have it that eyes of enzygotic twins find usually amazing similarity concerning a refraction etc.

Without denying a role of heredity in B.'s origin at all, nevertheless it is necessary to tell that recognition behind factors of external environment of crucial importance in formation of a clinical refraction of an eye, in particular B., in the course of ontogenesis most answers modern scientific views. According to some authors (E. S. Avetisov, etc.), the main reason for development of B. (in any case weak and average degrees) is the weakness of a tsiliarny muscle resulting from unfavorable conditions of visual work, and in this regard insufficiency of accommodation, and consecutive lengthening of a front-back axis of an eyeglobe can be considered as some kind of adaptive, compensatory act aimed at a possibility of long work at distance, close from eyes.

A clinical picture

All found B.'s cases can be divided on their degree into 3 groups: weak degree — to 3,0 dptr, average degree — from 3,0 to 6,0 dptr and high degree — from 6,0 dptr above. Occasionally B.'s cases to 20,0 — 30,0 dptr and even meet above. It is necessary to distinguish from high B. heavy, malignant, or progressing, B., at a cut these or those complications at the bottom of an eye, in its covers are available. The progressing B. always belongs to axial, but not to refraction. As in general in clinic it is necessary to deal preferential with axial B., it must be kept in mind that lengthening of an axis of an eye on 1 mm involves strengthening of a refraction on 3,0 dptr, or that the same, strengthening of a refraction on 1,0 dptr corresponds to lengthening of an axis of an eye on 1/3 mm.

Cases of weak and average degree of B. most often occur among total number short-sighted, more than a half known belong to B. combined. B. high degrees, progressing, followed by various complications, it is treated as morbid condition, a cut it can be caused by inborn inferiority of body or acquired under unfavorable external conditions owing to which lengthening of a front-back axis of an eye with the subsequent development of degenerative and atrophic changes in its fabrics and covers became possible.

Extremely frequent symptom at B. are the so-called «the flying front sights» seen by the patient in the form of the small grayish opacifications moving at the movement of an eyeglobe.

Fig. 1. Back double cone
Fig. 4. True back staphyloma.

At B. of averages and especially high degrees outward of eyes has some characteristic signs: eyeballs will stand a little forward, the palpebral fissure seems more widely, than normal, the anterior chamber of an eye is deeper normal, a pupil — bigger diameter. At an oftalmoskopichesky research of a bottom of an eye even at weak degrees of B. as a result of relative stretching and an atrophy of covers of an eye, in particular a choroid, the so-called back cone, or a back staphyloma is often noted near an optic disk, and at high degrees of B. — a true back staphyloma (tsvetn. fig. 1 and 4). On the mechanism of development a back cone call distraktsionny, i.e. a cone from stretching.

Fig. 2. A back staphyloma and the central chorioretinitis with hemorrhage
Fig. 3. The central chorioretinitis with hemorrhages.

In mild cases at an oftalmoskopiya the sickle from the temporal party of an optic disk is visible white or yellowish color. In more hard cases in a choroid and in a retina around an optic nerve there is gradually progressing degenerative and atrophic process taking sometimes an extensive zone, including and the most important area of a macula lutea in the functional (visual) relation. Similar process can happen also in peripheral parts of an eyeground where development has it, however, smaller value for function of sight. At defeats of area of a macula lutea — a so-called miopichesky maculitis, or the central miopichesky chorioretinitis, owing to a rupture of small blood vessels repeated retinal apoplexies and even in a vitreous are quite often observed, and hemorrhages in tissue of a retina often do not resolve completely and on their place the spot (a black spot of Fuchs) is formed grayish or even black (in connection with the subsequent pigmentation) (tsvetn. fig. 2 and 3). Sight at this complication suffers strongly. At the specified changes in a retina as a result of the shift of nervous elements the metamorphopsia, i.e. vision of objects in the distorted look quite often is observed.

The heaviest complication at B. is amotio of a mesh cover (see). This complication which is found usually only at average and high degrees of B. sharply reduces sight and can lead to a total blindness if surgery is not timely made, edges will be provided by the return prileganiye of the exfoliated retina. Any conservative treatment is usually unsuccessful.

Diagnosis

B.'s Diagnosis is based on data of an objective research by means of so-called shadow test (see Skiaskopiya) and by means of special devices — refractometers (see. Refractometry of an eye ), and also on the basis of subjective indications investigated in the course of definition of visual acuity using corrective B. of lenses (see. Visual acuity ).

Treatment

the Vast majority of cases of B. demands only correction by glasses; the progressing, malignant B., in addition to correction, demands also systematic general and topical treatment. At faces with a malignant current B., especially at children, symptoms of the general diseases of an organism quite often are found; at atherosclerosis, a hypertension, a climax, etc. B. accepts an adverse current. These diseases are the burdening factors capable to lead to a number of complications in a miopichesky eye.

A problem of correction of B. — first of all to improve sight of a short-sighted eye by means of optical glasses (see. Points ) and by that to put it or to bring closer at least to conditions of sight of an emmetropichesky eye.

Most of authors considers that it is necessary to appoint glasses, completely corrective B. Full correction provides not only the highest visual acuity, greatest possible for this eye, but also recovers proper correlations between convergence and accommodation, favorably influencing thereby many fiziol, processes in an eye. Short-sighted weak and average degrees during the work with a subject which is at a short distance from eyes can not use points or it appoints glasses on 1,0 — 2,0 dptr weaker, than necessary for a distance.

Speaking about full correction of B., it is necessary to specify, however, that the persons suffering from B. can not always transfer at constant carrying full correction by glasses. Children and teenagers, as a rule, without effort transfer full correction and with success use it both at weak, and at average degrees B. If points are appointed for the first time at more advanced age and at B. not of weak degrees, then distance spectacles, completely corrective B., can be transferred by them well, however use of these points for occupations can be difficult. It is connected with the fact that at full correction occupations at a short distance require inclusion of accommodation. Eyes of young people with a good volume of accommodation without any effort reach necessary rate of strain of accommodation. Young people can work is long also without the unpleasant phenomena of exhaustion of eyes. At short-sighted the volume of accommodation is less than advanced age and therefore they often do not transfer full correction for a bliza. In similar cases appoint points which not completely korrigirut B.

At high degrees of B. (higher than 6,0 dptr) full correction sometimes is badly transferred; even for a distance it is necessary to appoint those points which are practically transferred and, whenever possible, give satisfactory visual acuity. Points, not quite corrective high B., are most often used at the same time for a distance and for occupations at a short distance. It is in some cases better to have distance spectacles, whenever possible completely corrective B., and points on 2,0 — 3,0 dptr is weaker — for work close.

At appointment short-sighted points often it is necessary to consider the weakness of internal direct muscles which is available for them and to decenter glasses (to increase center distance of glasses by 1 — 2 mm) to facilitate visual work at a short distance. At such detsentrirovka prismatic effect of glasses facilitates work of internal direct muscles of an eye. Corrective glasses of the disseminating action are produced most often in the form of convexo-concave (so-called meniscuses, punktalny glasses, etc.). Their optical action is more perfect, than effect of earlier applied biconcave glasses. Convexo-concave glasses eliminate a so-called astigmatism of slanting beams more fully and korrigirut not only a motionless eye, but also making these or those movements at the changing directions of a look.

At high B. and considerable decrease in visual acuity (lower than 0,2 with correction) usual points often do not give due improvement of sight especially as full correction in these cases is badly transferred; increase visual acuity by means of a so-called telescopic spectacles. They have outward of the small field-glass which is put on like points. The telescopic system represents individually picked up combination of a dispersing lens (as an eyepiece) with a converging lens (as a lens) — by the principle of opera glasses or the galileevsky telescope. Feature of similar points is an opportunity to receive full correction of B. that provides the correct focusing of the image on a retina, promotes increase in sight. Besides, the telescopic system gives a nek-swarm increase (approximately by 1,7 times) images of objects on a retina (what usual corrective glass does not give) that also creates more favorable conditions for sight. A negative side of a telescopic spectacles is restriction of a field of vision at their use; besides, they are bulky. During the use of a telescopic spectacles work close requires a special nozzle (i.e. an attachment lens); practically only one eye (monocular sight) works at the same time.

By means of the contact lenses which are putting on directly a front surface of an eyeglobe (for eyelids), perhaps bigger, in comparison with ocular glasses, improvement of correction of B., especially high degrees.

At B.'s treatment it is necessary to carry out to lay down. - professional, actions, development and progressing to some extent detaining B. Apply means, the promoting rassasyvaniya of decomposition products of the damaged fabrics and the stimulating visual and nervous elements in a varying degree damaged to treatment of various complications (degenerative and atrophic changes in the covers of the stretched miopichesky eye) which are found at B., but capable to function at the level lowered in comparison with norm.

As resorptional means of a systemic effect use various drugs of iodine inside in small doses. Locally, in the form of eye drops, 1 — 10% solutions of dionine are widely applied. Dionine in the form of 2 — 5% of solution is applied also to subconjunctival injections. Under a conjunctiva also enter 3 — 5% solution of sodium chloride on 0,5 ml. Introduction under a conjunctiva of oxygen (a so-called oxygenotherapy) practices.

As excitant is appointed by subcutaneous injections of vitamin B 1 (5% solution) on 1 ml, on a course to 25 — 30 injections. Broad application is found by treatment by biogenic stimulators (across Filatov) in the form of injections of extract of an aloe, a placenta, FIBS, a peloidodistillyat (on 1 — 2 ml daily; on a course 30 — 45 injections with repetition in 2 — 3 months; 4 courses a year). V. P. Filatov put forward the idea of need of early and systematic use of fabric therapy for not only treatments by the complicated B. but also as the action, capable, in his opinion, in a varying degree to prevent development and progressing B.

At bent to hemorrhages in covers of an eye and in a vitreous it is necessary to resort to purpose of antihemorrhagic means (redoxons and P, Rutinum, etc.).

In 60 — the 70th years of the 20th century in foreign and domestic literature there were messages on attempts in the surgical way to suspend the progressing stretching of a sclera of a short-sighted eye and, thus, to avoid progressing of pathological process in a mesh cover. For these purposes the cadaveric wide fascia of a hip and a cadaveric sclera were usually used.

The forecast

At B. of weak and average degree the corresponding correction allows to keep working capacity. At B. of average degree with a tendency to progressing and high degree the forecast generally depends on possible complications. The forecast at malignant B. is adverse, at a cut pathological changes on an eyeground quite often tend to progressing.

Prevention

the Correct point of view in a question of genesis of B. has essential value for the organization of fight against B. and prevention of its development. Recognition behind environmental factors of major importance for B.'s development brings the most serious reasons under all set a dignity. - a gigabyte. the actions which are carried out for the purpose of the prevention of development and progressing B. Among these actions which implementation is especially important in relation to children of school age it is necessary to specify the following. Excessive approach of a subject of occupations to eyes, connected besides with a strong ducking forward (down), shall be limited; it is necessary to care for sufficient and rational natural and artificial lighting at schools and workrooms, for the device of convenient school desks and benches, for the correct position of a trunk of the school student during the occupations. Quality of printing of school textbooks is of great importance (see. Sight , hygiene).

Persons with the complicated B. should avoid everything that can cause rush of blood to the head; it is reasonable to protect the head from direct sunshine; at bright lighting it is necessary to use the darkened points (corrective filters) of average intensity. Such persons shall avoid, whenever possible, physical. tension and sharp movements for protection from possible hemorrhages and amotio of a mesh cover.

The duty is of great importance; occupations shall be organized so that for each 40 — 45 min. visual work it was necessary to 10 — 15 min. full rest for eyes. Important rational and well thought over lighting sufficient on force and well lighting workplace and a subject of occupations, but leaving head and a face in a shadow. It is not necessary to bend close to a subject of occupations (whenever possible, 30 — 35 cm are not closer). The correct landing providing normal respiration and blood circulation shall be one of the conditions necessary for normal development of the growing organism.

Often there is a question of choice of profession for short-sighted, graduating from high school, and this question quite often ask behind consultation the oculist. At choice of profession short-sighted young people should give preference to specialties and those industries of work where visual and physical. loading is easier where it is less shown requirements to sight.

The sparing operating duty (restriction of the working day) is necessary for persons with the progressing B. and changes at the bottom of eyes. However total failure from work in most cases is not advisable; transition to disability and total failure prof. of work do not guarantee against usual how he shows experience, a stop of process or the prevention of a disease of other eye at defeat of one at all. This question, very serious from the point of view of labor examination, it is necessary to solve individually; in each separate case it is necessary to take into account not only a condition of eyes and character of a profession, but also the general condition of an organism.

Some of the complications caused by B. can demand surgical treatment. Operational treatment is shown at amotio of a retina. It is necessary to resort to surgical treatment for removal of the complicated cataract which is quite often developing in eyes with heavy short-sightedness.

See also Eye , Refraction of an eye .


Bibliography: Averbakh M. I. Ophthalmologic sketches, page 220, etc., M., 1949; Avetisov E. S. Protection of sight of children, M., 1975, bibliogr.; Avetisov E. S. and To about l of l yu x V. A. Kliniko-genetichesky researches at short-sightedness, in book: Vopr, oftalmogenetik, iod of an edition of E. S. Avetisov, page 51, M., 1973; Aksenfeld T. The guide to eye diseases, the lane with it., page 89, M. — JI., 1939; Dashevsky A. I. Short-sightedness, JI., 1962, bibliogr.; Dymshits JI. A. Fundamentals of ophthalmology of children's age, D., 1970, bibliogr.;' Kovalyova and YB. I. Children's ophthalmology, M., 1970; The Multivolume guide to eye diseases, under the editorship of V. N. Arkhangelsky, t. 1, book 1, page 252, M., 1962; Radzikhovsky B. L. Astigmatizm of a human eye, M., 1969, bibliogr.; Der Augenarzt, hrsg. at. To. Velhagen, Bd 2, Lpz., 1972; Badt-k e G. Myopieprobleme, in book: Zeitfragen d. Augenheilk., S. 338, Lpz., 1953; Fran-goisJ. et Goes F. Biomitrie de la myopie, Ophthalmologica (Basel), t. 167, p. 49, 1973; System of Ophthalmology, ed. by S. Duke-Elder, v. 5, L., 1970; Thiel R. Atlas der Augenheilkunde, S. 196, Lpz., 1947.

M. L. Krasnov.

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