Myopia

MYOPIA, nearsightedness (from Greek myo - to squint and ops - eye; it has long been noted that by squinting their eyes, nearsighted people see better), an anomaly of refraction (see), in which the disproportion between the length of the eye and its refractive power is expressed in the predominance of the former over the latter. Due to this, a bundle of parallel rays emanating from infinitely distant objects, for which the normal eye is set, will gather in the nearsighted eye at a focus located not on the retina, but in front of it, at a distance greater the greater the myopia. The rays, continuing their path from this focus to the retina, produce on it not a point, but a circle of light diffusion. Only rays requiring greater refraction than parallel ones, i.e., diverging rays—such as rays emanating from an object located close to the eye—can gather into a point on the retina of such an eye. The point in front of the eye from which the emanating rays have precisely the degree of divergence necessary for these rays, upon refraction in the eye, to gather right on the retina, will be the point for which the given eye is set, i.e., the far point of distinct vision of the given eye. Everything lying beyond this point is seen by the nearsighted eye in circles of diffusion, i.e., unclearly. This point determines the degree of myopia. The closer it is to the eye, the stronger the myopia. In order for the nearsighted eye to see distant objects emitting parallel rays, these rays must be made to diverge, i.e., a diverging lens must be placed in front of the eye. A lens providing such divergence of parallel rays as corresponds to the divergence of rays emanating from the far point of distinct vision of the nearsighted eye will determine the degree of myopia of the given eye. This will be a diverging lens (concave) with a focal length equal to the distance of the far point of distinct vision. Thus, the degree of myopia is determined by the position of the far point of distinct vision, and the latter shows the focal length, i.e., the number of diopters by which the given nearsighted eye must be weakened to make it normal (emmetropic). Without denying the existence of pure refractive myopia, i.e., that which is caused by an excessively strong refracting apparatus of the eye at its average normal length (22–23 mm), one can safely say that in clinical practice, as a rule, one deals with axial myopia, in which, with an average more or less constant power of the refracting apparatus, the anteroposterior axis of the eye is longer than normal. One can even assume without significant error that every diopter of myopia corresponds to an elongation of the eye axis by ¹/₃ mm. Of course, this is nothing more than a schema from which clinical practice cannot demand mathematical precision, and due to certain individual fluctuations in optical constants, the eye refraction can fluctuate at one and the same eye length within the limits of several diopters. From the standpoint of the theory of the hereditary origin of clinical refraction, this fact explains why the progeny of the same parents exhibit refractions that do not precisely repeat the refraction of either the paternal or maternal lines: the dioptric apparatus with its constituent parts and the length of the eye can represent separate genes and, consequently, the paternal dioptric elements, combining with the maternal length, or vice versa, will yield refractions that are not precisely present in either the paternal or maternal line. With the growth of the eye length, the mismatch between the power of the refracting apparatus and the position of the retina in the eye increases. This mismatch can be expressed solely by an increase in the degree of myopia, i.e., an increase in the lens required to correct such myopia, without the light-sensitive apparatus of the eye suffering and visual acuity dropping. This is benign myopia. But the growth of myopia can be accompanied by a whole series of complications, some relatively benign, others very severe (malignant myopia — myopia gravis), capable of leading the patient not only to the loss of working capacity, but even to complete blindness. These complications are as follows: 1. Accommodation spasm, due to which myopia appears greater than it actually is. It was incorrectly considered the culprit of myopia. True, it usually occurs in young myopes during the period of myopia growth and not infrequently precedes the objective development of myopia in children and schoolchildren, causing various unpleasant asthenopic phenomena. — 2. Muscular asthenopia. The myope, forced to keep the object of study close to the eyes, imposes too much work on the internal rectus muscles of the eye. Their fatigue can be so great that they refuse to work; then one eye drifts outward, and the myope shifts the object of study to the side of the other eye, with which they continue to work without the participation of convergence, i.e., the work of the internal rectus muscles. Thus, a common occurrence in myopes is insufficiency of the internal muscles, which find it difficult to turn large nearsighted eyes with a high demand for convergence. On this basis, myopes often develop strabismus, which in these cases is most often divergent (strabismus divergens): due to a complete breakdown in impulses for convergence and accommodation (the stronger the myopia, the less accommodation is needed and the more convergence is required), the myope sets one eye by accommodation and the other by convergence, i.e., transitions from binocular work to monocular, and the already developed insufficiency of the internal muscles directs the eye toward the temple. This true divergent strabismus should not be confused with the apparent convergent strabismus frequently observed in myopes, especially of high degrees: due to poor centering of the eye, the axis passing through the center of the pupil always forms a certain angle ($oldsymbol{ u}$) with the visual line, i.e., the line connecting the macula lutea with the fixation point. In large nearsighted eyes, this line usually passes lateral to the center of the pupil. Thus, with completely correct binocular fixation by both visual lines, an observer judging the position of the eyes by the arrangement of the pupil centers gets the impression that the eyes are crossed inward, whereas in reality no strabismus, i.e., absence of intersection of the visual lines on the fixed point, exists. However, in myopes, especially of high degrees, true convergent strabismus is also encountered. — 3. Floaters (mouches volantes), swimming in any vitreous body as invisible dead cells, due to the hyperesthesia of the retina of nearsighted eyes and due to the greater distance from the retina in the long eye, cast large, unpleasantly perceived shadows when looking at bright objects and surfaces. — 4. Posterior conus, posterior staphyloma. In mild cases, we are dealing with the appearance of a white crescent on one side, usually the temporal side, of the optic nerve papilla. Here, essentially, there are no atrophic changes in the deep membranes of the eye. This conus is simply an expression of the unfolding of the scleral canal of the optic nerve during eye growth. The wall of this canal during ophthalmoscopy looks like a white crescent at the disc. Such a conus is not accompanied by any visual disturbance. It can also be present in a non-nearsighted eye. In severe cases, a genuine progressive degenerative-inflammatory process occurs around the disc in the choroid and, partly, the retina with their atrophy, especially the former, with thinning, softening, and protrusion of the sclera [sclerotico-chorioiditis posterior, staphyloma posticum verum, see table (pp. 531–532), Fig. 3]. The staphyloma forms either on one side of the disc or on all sides unevenly. It is mostly accompanied by a more severe complication, namely, — 5. Chorioretinitis centralis (maculitis) myopica [see table (pp. 531–532), Fig. 4], which represents approximately the same inflammatory-degenerative-atrophic process in the macula lutea, with recurrent hemorrhages into the retina and vitreous body, opacities of the latter, either fixed or floating, and leads in the vast majority of cases to the destruction of the macula lutea, i.e., to the loss of central vision. The disease begins with a complaint of a suddenly appeared spot in front of the eye and metamorphopsia, i.e., distortion of an object, font, etc., and ends with the loss of the ability to read and perform fine work. But the most bleak complication of malignant myopia is retinal detachment. — 6. Retinal detachment. According to some statistics, the frequency of detachment reaches 5% of all myopias exceeding 10.0 D. The disease begins almost always with a sudden and seemingly causeless loss of a significant part of the visual field or even complete loss of vision. Rarely, it is preceded by the sensation of fiery flashes and zigzags for several days. Objectively, some time before the appearance of detachment, it is possible to ascertain an uncharacteristic hypotonia for the given eye, which persists for a long time even after the onset of detachment. After some fluctuations of improvement and worsening, myopic detachment, with extremely rare exceptions, ends in complete blindness of the eye, accompanied by a whole series of sequential complications (cataracts, iritis, etc.).

The last two complications of myopia, especially the lesion of the macula, are all the more terrible because they have a great tendency sooner or later to become bilateral. Thus, the question arises whether that myopia which simply represents an anomaly of refraction requiring only correction with glasses, and that malignant myopia which occupies such a prominent place among the causes of blindness (especially occurring at the age of 40-50 years and older), are simply different degrees of the same pathological state or whether they are completely different states that share the elongation of the eye. At present, clinical practice is close to recognizing the correctness of the latter point of view. True, malignant myopia is mostly high myopia, but severe changes in the retina and choroid are far from rarely seen in medium and even low degrees of myopia, and myopia gravis in only one eye is frequently ascertained as a very early and even congenital condition. A gradual increase in myopia and its subsequent transition into a malignant form is almost never observed in clinical practice. If myopia turns out to be malignant already in childhood or young years, then tuberculosis or other severe lesions of the organism are very often simultaneously ascertained in the given subject. In other cases, malignancy is discovered at an age when the climax, arteriosclerosis, etc., are new factors affecting the previously healthy membranes of the eye. It is very difficult for the clinician to decide whether the eye is diseased with myopia or whether it is myopic because it is diseased. Origin of Myopia. The existing theories are based primarily on long-established facts and observations: 1) people are born mostly hyperopic and, in any case, not myopic; 2) there are fewer myopic individuals in primary school than in secondary and higher schools; 3) with the grade, the number of myopic individuals and the degree of myopia increase; 4) in various industries and enterprises, a large number of myopic individuals are observed in those workshops where there is prolonged intensive work at a close distance. Hence the conclusion was drawn: work at a close distance produces myopia. Thus the doctrine of school and occupational myopia was formed—a hypothesis that firmly seized the minds of ophthalmologists, hygienists, and educators. But this opinion has not been able to definitively establish itself to this day, primarily due to the impossibility of finding a factor that would explain exhaustively, without running into destructive contradictions, the elongation of the eye under the influence of work at a close distance. After greater or lesser criticism and polemics, such assumptions as an increase in intraocular pressure in general, caused by accommodation, convergence, the role of internal and external muscles, and the superior oblique, gradually fell away. Even less convincing is the influence of a number of anatomical factors, such as the width of the skull and the large distance between the eyes, a low orbit, a short optic nerve, etc. All these are moments present in one subject and completely absent in the majority of other myopes. Neither did the later, seemingly very plausible hypothesis of Levinsohn regarding the pulling action of the gravity of the eye in a tilted head position and orbital hyperemia gain recognition. This theory was unconvincing despite the fact that painful experiments on growing monkeys sometimes succeed in producing the development of myopia and even the formation of changes in the fundus resembling myopic ones. Each of the put-forward theories has its own special, weighty, unrefuted objections, but all of them together do not explain one simple fact: the development of myopia in only one of the two eyes. The gathering of material on myopia gradually undermined the doctrine of occupational myopia: 1. A considerable number of children are born myopic and even to a high degree (Henry), and severe myopia in one eye is very often congenital. 2. Very often myopia is detected in preschool children. 3. Myopia was widespread among our most distant ancestors. 4. Among Papuans and cannibals, who know neither literacy nor any craft, Wick observed a large number of myopes and even of high degrees. Among the native population of Egypt, the number of myopic individuals is no less than in the most cultured countries of Europe (Meyerhof). 5. High degrees of myopia are encountered equally frequently among Swedes and Finns, despite the well-known difference in their cultures (the opinion of Heinonen, who lives among them). Among Copts in Egypt, a huge number of myopics are found (Druault-Toufesco), while the Nubians and Sudanese living nearby under the same conditions almost do not know myopia (Meyerhof). 6. Among the peasants of the Moscow Governorate of conscription age, Dr. Vasmut encountered a large number of myopics. They were pure agriculturists, illiterate, knowing no craft, who did not go to school because of poor vision even before school. Similarly, Prof. Ochapovsky found 1% of moderate and high myopes among the agricultural population of the Kuban. 7. Among domestic animals, both small and large (rabbits, dogs, pigs, sheep, horses, cows), as well as among wild predatory beasts, there are not a few myopes, sometimes from birth (in domestic animals myopia occurs in over 30%). 8. The model gymnasium in Giessen, organized and built according to all the requirements of school hygiene and engineering, nevertheless yielded 12.5% myopia and an increase of it in 57.5% of already myopic students. The degree of increase of myopia in schoolchildren working under ideal conditions and under poor conditions is almost identical (Mortimer). Despite the colossal progress of hygienic knowledge and the annual growth of requirements placed on students, myopia among medical students in 1902 constituted the same 60% as in 1866 (Cohn). 9. The progression of myopia in secondary school from year to year is observed mainly in those schoolchildren in whom myopia was already ascertained in the lower grades. 10. Severe forms of myopia with lowered vision are most often encountered not in professions associated with fine work at a close distance, but among merchants, clerks, etc., who go into these professions from childhood because of poor vision. 11. Children of the same family, living and working under completely identical conditions, some become myopic, others remain normal or hyperopic. 12. Workshops giving a high percentage of myopia in one factory or enterprise unexpectedly reveal diametrically opposite figures in another production and enterprise. 13. The eyes of identical twins exhibit striking similarity not only in refraction, but even in corneal radii and the degree of myopia (Ivanova). All the cited facts show with indisputable clarity: I. Myopia can arise and develop independently of work at a close distance. II. Myopia is based on congenital factors that manifest myopia either at birth or are discovered later. In this regard, the following facts are interesting: 1. In high myopia, in 82 (Lutkevich) and even 88% (Schmidt-Rimpler) of cases, myopia exists in one or both parents. 2. If a thorough examination of genealogical (pedigree) trees is performed, in rare cases it is not possible to discern dominant or recessive hereditary transmission. 3. A thorough examination of workshops where a high percentage of myopia is found shows that among the children and blood relatives of workers in these workshops, the percentage of myopia is significantly higher than among the children and relatives of workers in other workshops. 4. There are hundreds of family cards showing that each family, each lineage is characterized by its own basic refraction, deviations from which occur insofar as new elements flow into the family (Auerbach). Thus, myopia is a condition that is not only congenital but also hereditary. Occupational myopia as such does not exist; work at a close distance, if it plays a role, is secondary, contributing where there is a congenital predisposition to myopia. The number of defenders of pure occupational myopia decreases every year. Hippel is right when he asserts that already at the moment of the spermatozoon's encounter with the ovum, the question of the future human's refraction is decided. What is inherited in myopia is still an open question; of course, a whole series of anatomical and physical properties, perhaps (Vogt) the tendency of the normal retina to postembryonic growth, which entails an enlargement of the eye (axial myopia). Simultaneously with this, a congenitally lowered capacity of the elements of the retina and choroid may be inherited (malignant myopia). If one adopts this point of view, the question of the prophylaxis of myopia becomes primarily a eugenic question. Individuals suffering from malignant myopia must firmly remember that they have many chances to transmit this sometimes severe disease to their children and must draw appropriate conclusions from this. This does not diminish the significance of our sanitary and hygienic measures in schools and industries in the least. These measures have the purpose of preventing myopia and its progression; but the effect of these measures is not direct.

They are necessary insofar as they affect the general physical and mental development and condition of the schoolchild and the worker. These measures acquire a completely special, paramount significance in the prevention of myopia in the eyes of those hygienists and ophthalmologists who consider work at close range to be the primary factor producing the elongation of the eye along the anteroposterior axis. Everything that contributes to the prolonged approximation of the eyes and head to the object of study must be carefully eliminated both in school and at the factory. Anything that requires prolonged, motionless work in enclosed spaces, especially with an inclined position of the head and torso, is harmful. Hence the concern for natural and artificial illumination, for the design of desks and benches, for the position of the head and torso, for print, textbooks, and writing supplies, for the quantity and quality of work, for work breaks to rest the muscles and blood vessels of the eye and orbit (school hygiene), and for lighting, the improvement of technology and production tools, and vocational selection (occupational hygiene). Treatment. Here the primary issue is not the treatment of existing myopia, but its correction with glasses. Only that eye is in a condition of normal nutrition and circulation in which the ciliary muscle functions normally. Such is the emmetropic eye; such can become the myopic eye to which a lens is fitted that fully corrects its ametropia. The material accumulated over the last 3-4 decades undoubtedly shows that full correction of myopia for constant wear, if it does not prevent the development of myopia, at least, according to large statistical figures, results in significantly smaller increases in it than the absence of correction or incomplete correction. The results of full correction are better 5G1 and it is more pleasant and acceptable to the patient the earlier it is applied. Unaccustomed to work due to the disuse of accommodation, the ciliary muscle develops poorly or atrophies, and such an eye, having immediately received a full correction requiring the free play of accommodation, does not tolerate this correction and feels poor. Also of some significance in this regard is the somewhat unusual reduction and alteration of objects caused by strong concave lenses. In such cases, full correction must be approached gradually, making greater or lesser individual departures, especially for near work. Correction in myopia frequently increases vision tenfold or more, and refusal to wear glasses should rarely be taken seriously. In the vast majority of cases, the refusal is based on prejudices. In view of the fact that myopes mostly suffer from insufficiency of the internal rectus muscles, it is better to set the lenses so that their centers lie outward from the centers of the pupils: the resulting prismatic action of the lens facilitates the work of the weak muscle. The treatment of severe complications of myopia involving the choroid and retina cannot yet claim particular success. Dionin in the form of drops (3-20%) or, better, subconjunctival injections (1-10%), iodine preparations internally, and local bloodletting produce either temporary significant improvement, or only subjective improvement, or none at all. Proper posture, the absence of blood surges to the head, the prohibition of alcohol, and physical exertion have their own rationale. The prohibition of reading and eye work in general is hardly based on objective data. Complete cessation of studies does not guarantee the cessation of the process or the prevention of disease in the second eye, just as the continuation of studies is hardly the true cause of relapses and the progression of the process. It is a matter of the physician's tact in each individual case to decide this question based on the totality of all individual physical and mental factors. But, like any diseased organ, eyes with malignant myopia should be recommended as much rest as possible. Originating from the idea of abbot Desmouceaux and having survived a period of colossal enthusiasm at the end of the last and the beginning of the current century, the surgical treatment of high myopia is rarely used at present. Accumulated experience has shown (Lutkevich) that not only does it not improve or prevent the severe complications of myopia, but it even probably contributes to them. The treatment consists in the removal of the crystalline lens, which reduces myopia by 14-15 diopters. In any case, the idea of surgical treatment may occur to the physician in cases of myopia of no less than 20 diopters.