Myopia is a disease in which a person poorly distinguishes objects located at a distance. With myopia, the image does not occur in a specific area of the retina, but is located in the plane in front of it.
Currently, there is no single scientific concept of the emergence and development of myopia. The most recognized is the three-component hypothesis of the origin of myopia, according to which three links play a role in its development:
1) visual work at close range combined with weakened accommodation;
2) hereditary condition of myopia;
3) the effect of intraocular pressure (IOP) on a weakened sclera.
There are such types of myopia:
- Depending on the severity:
- weak (from -0.25 to -3.0 diopters);
- average (from -3.25 to -6.0 diopters);
- high (more than -6.0 diopters).
- Depending on the clinical course:
- non-progressive (stationary);
Non-progressive myopia is an abnormality of refraction, which is clinically manifested by a decrease in distance vision, well corrected and does not require treatment. If during the year the degree of myopia increases by more than 1.0 diopters, myopia is considered progressive. Continuous progression (the degree of myopia continues to increase throughout life) is called malignant myopia, or myopic disease. This is a disease that requires treatment and leads to visual disability.
The clinical picture of myopia is associated with the presence of the primary weakness of accommodation, the overstrain of convergence and stretching of the eyeball, which occurs after the eye stops growing (after 10-12 years) and leads to anatomical and physiological changes in the eye. The greatest risk of developing myopia occurs between the ages of 8 and 20 years.
Since the myope examines objects only at close range, the eye is constantly forced to converge. Moreover, its accommodation is at rest. The inconsistency between convergence and accommodation can lead to fatigue of internal rectus muscles and the appearance of visual fatigue – muscular asthenopia (myopes cause headache and eye fatigue during work), as well as the development of heterophoria, monocular vision and divergent concomitant strabismus.
Anterior-posterior axis of the eye with myopia can be extended up to 30-32 mm or more. Stretching the eyeball leads to an expansion of the palpebral fissure, resulting in the impression of a small puiglasia. The sclera becomes thinner, especially in the area of attachment of the lateral muscles and near the edge of the cornea, which can be seen with the naked eye on the bluish tinge of the sclera due to translucency of the choroid. Occasionally, anterior staphyloma of the sclera may occur. The cornea is also stretched and thinned. The anterior chamber of the eye deepens. Iris tremor (iridodone) may occur. Destruction or liquefaction occurs in the vitreous – the vitreous fibrils are thicken, disintegrate, stick together to form conglomerates. The shade of such cells on the retina in a stretched myopic eye is more than in the eyes with a different refraction, so myopic people often complain of “flying flies” (muscae volitantes), “threads”, “balls of wool” before their eyes. In the fundus of the eye, depending on the genesis and degree of myopia, the following changes occur: near-disc light arc reflexes; myopic cones; rear staphyloma (false and true); changes in the yellow spot of the retina; peripheral retinal degeneration; retinal disinsertion.
The myopic cone is a small rim in the form of a sickle at the temporal edge of the optic nerve head, which results in stretching the sclera and atrophy of the pigment epithelium layer located near the disk. The retinal pigment epithelium and choroid lag are behind the edge of the optic nerve head, and the stretched sclera shines through the transparent retina.
False staphyloma occurs as a result of an increase in myopic cones that enclose the optic nerve head in the form of a ring (usually of irregular shape). With a high degree of myopia, protrusions of the posterior pole of the eye, namely true staphylomas, are formed.
As a result of stretching the posterior segment of the eyeball in the choroid, cracks form in the form of yellowish or whitish stripes, then degenerative changes appear in the retina in the form of white polymorphic, often merging lesions with pigment clumps among themselves. Stretching of the eyeball is accompanied by increased fragility of the blood vessels, which leads to hemorrhages (hemorrhages) in the retina and subsequently the appearance of chorioretinal foci. The formation of a coarse pigmented focus in the area of the yellow spot at the site of hemorrhage (Fuchs spot) is the cause of a marked decrease in visual acuity, the appearance of metamorphopsy in patients (curvature of visible objects).
These changes are called myopic chorioretinal dystrophy. Vitreous hemorrhage leads to clouding; there may be detachment of the vitreous body, the development of complicated cataracts. Myopia may be accompanied by pathological changes and at the extreme periphery of the fundus – peripheral chorioretinal dystrophy, which often causes retinal breakdown and detachment (in 60% of cases retinal detachment occurs in myopic eyes).
The identification of individuals with an increased risk of myopia is very important. This group includes children who already have myopia; they carry out special exercises for the training of accommodation. It is also important to observe the labor regime. With the progression of myopia, it is necessary that for every 40-50 minutes of reading or writing there should be at least 5 minutes of rest. With myopia above 6.0 diopters, the visual load time should be reduced to 30 minutes, and the rest increased to 10 minutes.
The basic preventions are the following:
- Early detection of myopia and clinical examination of identified patients.
- Timely rational correction of myopia.
- Creation of conditions for classes that meet sanitary and hygienic standards.
- Improvement, general strengthening and physical development of the body, detection and treatment of associated diseases.
- Limitation of the visual load and the correct alternation of work and rest.
For mild myopia, full correction is recommended, equal to myopia. Eyeglass correction can be used only when necessary. In case of myopia of medium and especially high degree, a constant correction is assigned.