What causes myopia?

In the etiology of congenital myopia, the leading role is given to heredity (55-65%) and perinatal pathology.

Congenital myopia is usually characterized by a high degree, an increase in the length of the anteroposterior axis, anisometropia, astigmatism, a decrease in maximum corrected visual acuity, changes in the fundus associated with developmental anomalies of the optic nerve and macular region.

Acquired myopia appears in preschool (early acquired), school age, less often in adults, and its occurrence and progression is based on the elongation of the anterior-posterior axis of the eye.

In most cases, the visual acuity of the nearsighted eye, under optical correction with diverging lenses of the appropriate diopter, increases to normal values (1.0 or 6/6 or 20/20, depending on the measurement system). Such myopia is called uncomplicated. With complicated myopia, visual acuity not only at a distance but also at a close distance remains reduced even with full optical correction of refractive error. Such uncorrectable vision loss can be caused by amblyopia (cortical inhibition), dystrophic changes in the central part (macular zone) of the retina, its detachment, and clouding of the lens (cataract). In children, the most common cause of uncorrectable vision loss with myopia is amblyopia. It accompanies only congenital myopia of a high and, less often, moderate degree. The reason for its development is the prolonged projection of unclear images onto the retina (refractive amblyopia). An even more persistent decrease in vision is observed with anisometropic or unilateral congenital myopia (anisometropic amblyopia).

In addition to amblyopia, uncorrectable decrease in visual acuity in congenital myopia may be caused by organic changes in the visual system. Congenital myopia is often combined with various types of pathology and anomalies in the development of the eye (nystagmus, strabismus, colobomas of the optic nerve, eye membranes, subluxation of the lens, partial or complete cataract, spherophakia, lenticonus, remnants of embryonic tissue, pathology of the retinal pigment epithelium, partial atrophy and hypoplasia of the optic nerve), as well as systemic ectodermal malformations and types of connective tissue dysplasia (Marfan, Stickler, Marchesani syndromes; blue sclera, chest deformity, flat feet, umbilical hernias, etc.).

Unlike congenital myopia, acquired myopia develops gradually, with a minor optical defect that initially reduces only distance visual acuity. The latter increases to 1.0 when weak diverging ("negative") lenses are applied. Near visual acuity with acquired myopia of a weak or even moderate degree remains normal and does not interfere with the correct development and maturation of the visual system. Amblyopia is not typical for acquired myopia.

In the etiology of acquired myopia, a combination of hereditary and environmental factors plays a role. In children of healthy parents, myopia is detected in 7.3% of cases, in 26.2% of cases with one nearsighted child, and in 45% of cases with both. Myopia is inherited in an autosomal dominant (usually low-grade, uncomplicated) and autosomal recessive manner (usually rapidly progressing, high, complicated).

At the same time, there is undoubtedly an influence of various environmental factors both on the occurrence of myopia and on the nature of its course.

Such factors may be various diseases, acute and chronic infections (especially those accompanied by hyperthermia, prolonged course, weight loss): hypovitaminosis, lack of complete proteins in food, physical inactivity, heavy physical and visually intense work; maternal illnesses during pregnancy, toxicosis, alcoholism and other intoxications. Prematurity and low birth weight are also often associated with the development of myopia. However, the most significant environmental factor is visual work at close range. In recent years, it has been proven that the incidence and progression of myopia are directly related to the number of hours spent reading (and the inverse relationship has been traced with hours of physical activity outside the home). It is a known fact that the population of "myopes" is reliably more read and educated, compared to the non-myopic (Grossvenor, Goss, 1999).

In addition to heredity, two other factors participate in the pathogenesis of acquired myopia: weakened accommodation and weakened sclera (Avetisov E.S., 1965). Accommodation disorders precede the development of myopia and accompany it. Various unfavorable environmental factors (poor hygienic conditions, various diseases, injuries that disrupt the blood supply to the ciliary muscle, physical inactivity) exert their influence through the accommodation apparatus.

Progressive myopia of medium and especially high degree is a disease of the sclera: disorder of its metabolism, microstructure, weakening of supporting properties. In the process of progression of myopia, stretching and thinning of the fibrous membrane of the eye (sclera) occurs, an increase in all its dimensions (anteroposterior, horizontal, vertical) and volume, a decrease in rigidity, acoustic, X-ray optical density. This process is accompanied by mechanical stress, stretching, damage to the inner membranes of the eye (choroid and retina), the development of dystrophic changes in them and in the vitreous body.