What causes myopia?

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

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

The acquired myopia appears in preschool (early-acquired). School age, less often - in adults, and the basis of its appearance and progression is lengthening anteroposterior axis of the eye.

In most cases, the visual acuity of the near-sighted eye under optical correction conditions by the diffusing lenses of the corresponding diopter is increased to normal values (1.0 or 6/6 or 20/20 depending on the measurement system). Such a myopia is called uncomplicated. With complicated myopia, the visual acuity not only in the distance, but also near to the refractive error, even with a full optical correction, remains reduced. This uncorrected 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 cause of uncorrectable vision loss in myopia is most often amblyopia. It accompanies only congenital myopia of high and, rarely, of medium degree. The reason for its development is the prolonged projection onto the retina of obscure images (refractive amblyopia). Even more persistent decline in vision is noted with anisometropic or one-sided congenital myopia (anisometropic amblyopia).

In addition to amblyopia, uncorrectable reduction in visual acuity in congenital myopia can 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, optic nerve colonies, eye membranes, lens subluxation, partial or complete cataracts, spherofakia, lenticone, embryonic tissue, pathology of retinal pigment epithelium, partial atrophy and hypoplasia of the optic nerve), as well as systemic ectodermal developmental defects and types of connective tissue dysplasia (Marfan, Stickler, Markesan syndrome, blue sclera, chest deformity , Flat, umbilical hernia and others.).

Unlike congenital, acquired myopia occurs gradually, with a slight optical defect, which first reduces only visual acuity in the distance. The latter rises to 1.0 with the attachment of weak scattering ("negative") lenses. The visual acuity near with the acquired myopia of weak and even medium degree remains normal and does not interfere with the proper development and maturation of the visual system. Amblyopia for acquired myopia is not typical.

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, with one short-sighted - in 26.2%, with both - in 45%. Myopia is inherited by autosomal dominant (often - low degree, uncomplicated) and autosomal recessive type (more often - rapidly progressing, high, complicated).

At the same time, undoubtedly the influence of various factors of the environment on the occurrence of myopia, as well as on the nature of its course.

Such factors can be various diseases, acute and chronic infections (especially accompanied by hyperthermia, prolonged course, weight loss): hypovitaminosis, lack of high-grade proteins in food, physical inactivity, heavy physical as well as visually-strenuous work; diseases of the mother during pregnancy, toxicosis, alcoholism and other intoxication. Prematurity and a small body mass at birth are also often associated with the onset of myopia. However, the most significant factor of the external environment is visual work at close range. In recent years, it has been proven that the frequency and progression of myopia are directly related to the number of hours spent reading (and feedback is tracked with hours of physical activity outside the home). The fact is known that the population of "myopes" is significantly more readable and educated, compared with non-miopic (Grossvenor, Goss, 1999).

In the pathogenesis of acquired myopia, in addition to heredity, two more factors are involved: a weakened accommodation and a weakened sclera (Avetisov ES, 1965). Accommodation disorders precede the development of myopia and accompany it. Through the accommodation apparatus, various unfavorable factors of the external environment (bad hygienic conditions, various diseases, traumas that disrupt the blood supply of the ciliary muscle, inactivity) realize their influence.

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