Age-related changes in refraction

In order to understand the nature of age-related changes in refraction, it is necessary to take into account that the refractive power of the eye optical device relative to the retina mainly depends on the length of the anteroposterior axis and the state of the accommodative apparatus.

In the general trend of age-related changes in refraction, two phases can be distinguished: hypermetropization of the eye (weakening of static refraction) - in early childhood and in the period from 30 to 60 years and two phases of myopia (strengthening of static refraction) - in the second and third decades of life and after 60 years.

First of all, it is necessary to dwell on the patterns of age-related changes in hypermetropic and myopic refraction. The most sensitive to such changes in accommodation are patients with hypermetropia. As noted above, in hypermetrops the mechanism of accommodation is included constantly, that is, when considering both closely and distantly located objects. The total amount of hypermetropia is composed of a hidden (compensated accommodation voltage) and an explicit (requiring correction). The ratio of these components varies due to age-related disorders in the accommodative apparatus: with age, the manifestation of sheer hypermetropia increases. In other words, ametropia does not increase and does not arise (so subjective can assess these changes patients), but manifests itself. At the same time, there are no changes in the parameters of the main anatomical and optic elements of the eye (the length of the anteroposterior axis, refraction of the cornea).

A completely different mechanism for the onset of myopia and such a phenomenon, very often observed in clinical practice, as its progression. The main anatomical substrate of this process is a gradual increase in the length of the anteroposterior axis of the eye.

Myopia can be congenital, manifested in preschool children, but most often occurs at school age, and with each year of schooling the number of students with myopia increases, and its degree is often increased. By the time of adulthood, about one-fifth of schoolchildren due to myopia is more or less limited to the choice of profession. The progression of myopia can lead to severe irreversible changes in the eye and a significant loss of vision.

ES Avetisov (1975) identifies three main links in the mechanism of myopia development:

1. visual work at close range - a weakened accommodation;
2. hereditary conditioning;
3. weakened sclera - intraocular pressure.

The first two links act already at the initial stage of development of myopia, and the degree of participation of each of them can be different. The third link is usually in the potential state and manifests itself in the stage of developed myopia, causing its further progression. It is possible that the formation of myopic refraction can begin with this link.

With a weakened accommodative capacity, enhanced visual work at close range becomes an unbearable burden for the eyes. In these cases, the body is forced to change the optical system of the eye in such a way as to adapt it to work at close range without the accommodation tension. This is achieved mainly by lengthening the anteroposterior axis of the eye during its growth and the formation of refraction. Adverse hygienic conditions for visual work have an impact on the development of myopia only to the extent that they impede accommodation and induce excessive eye contact with the object of visual work. With this mechanism of development, myopia usually does not exceed 3.0 Dpt.

The weakness of the accommodative apparatus can be a consequence of congenital morphological inferiority or insufficient training of the ciliary muscle or the effects on it of general disorders and diseases of the body. The reason for the weakening of accommodation is also the insufficient supply of ciliary muscle with blood. Decrease in its working capacity leads to an even greater deterioration of the hemodynamics of the eye. It is well known that muscle activity is a potent activator of blood circulation.

Possible as an autosomal dominant, and autosomal recessive type of inheritance of myopia. The frequency of these types of inheritance varies significantly. The second type is especially common in isolates characterized by a high percentage of related marriages. In the autosomal dominant type of inheritance myopia occurs at a later age, proceeds more favorably and, as a rule, does not reach high degrees. For myopia inherited in an autosomal recessive type, phenotypic polymorphism is characteristic, an earlier occurrence, a greater propensity to progress and development of complications, a frequent combination with a number of congenital eye diseases and a more severe course in the subsequent generation compared to the previous one.

When the sclera is weakened due to a violation of fibrillogenesis, which can be congenital or occurs as a result of general diseases of the body and endocrine dislocations, conditions are created for an inadequate response to the stimulus to the growth of the eyeball, and also for its gradual extension under the influence of intraocular pressure. In itself, intraocular pressure (even increased), in the absence of weakness of the sclera, can not lead to the dilatation of the eyeball, and not only static but also dynamic intraocular pressure, that is, "perturbation" of the eye's fluid with movements of the body or head. When walking or performing any workflows associated with visual control, these movements occur mainly in the antero-posterior direction. Since in the anterior part of the eye there is a barrier in the form of an "accommodation" ring, the intraocular fluid in "disturbances" affects mainly the posterior wall of the eye. In addition, as soon as the posterior pole of the eye assumes a more convex shape, in accordance with the laws of hydrodynamics it becomes the site of the least resistance.

Excessive lengthening of the eyeball has a negative impact primarily on the choroid and the retina. These tissues, as more differentiated, have less plastic capacity than the sclera. For their growth, there is a physiological limit, followed by changes in the form of stretching of these membranes and the appearance in them of trophic disorders, which serve as the basis for the development of complications observed at high degrees of nearsightedness. The appearance of trophic disorders is also facilitated by reduced hemodynamics of the eye.

Some features of the pathogenesis of congenital myopia are revealed. Depending on the origin, three forms are distinguished:

• congenital myopia developing due to the discrepancy between the anatomical and optical components of refraction resulting from the combination of the relatively long axis of the eye with the relatively strong refractive power of its optical media, mainly the lens. In the absence of weakness of the sclera, such myopia usually does not progress: the lengthening of the eye during growth is accompanied by a compensatory decrease in the refractive force of the lens;
• congenital myopia due to weakness and increased dilatability of the sclera. Such short-sightedness intensively progresses and is one of the most unfavorable forms in prognosis;
• congenital myopia with various malformations of the eyeball. In such cases, myopic refraction due to anatomical optic discordance is combined with various pathological changes and anomalies in the development of the eye (strabismus, nystagmus, colobolics of the eye, subluxation and partial clouding of the lens, partial atrophy of the optic nerve, degenerative changes in the retina, etc.). With a weakening of the sclera, such nearsightedness can progress.

As for the shift of refraction towards myopia in persons over 60 years of age, it is not noted by all authors. It remains an open question whether this shift is a natural age tendency or it is explained by a relatively large number among the surveyed individuals with a beginning cataract, in which, as is known, there is a swelling of the lens and an increase in its refractive capacity.

[1], [2], [3], [4], [5]