Age-related refractive changes

In order to understand the essence of age-related changes in refraction, it is necessary to take into account that the refractive power of the optical apparatus of the eye relative to the retina mainly depends on the length of the anterior-posterior 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 myopization (increasing 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. Patients with hyperopia are most sensitive to such changes in accommodation. As noted above, in hypermetropic patients, the accommodation mechanism is constantly on, i.e. when examining both close and distant objects. The total amount of hyperopia consists of latent (compensated by accommodation tension) and obvious (requiring correction). The ratio of these components changes due to age-related disorders in the accommodation apparatus: with age, the severity of obvious hyperopia increases. In other words, ametropia does not increase or arise (this is how patients can subjectively assess these changes), but manifests itself. At the same time, no shifts in the parameters of the main anatomical and optical elements of the eye (length of the anteroposterior axis, corneal refraction) occur.

A completely different mechanism of myopia development 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 anterior-posterior axis of the eye.

Myopia can be congenital, manifested in preschoolers, but most often occurs at school age, and with each year of schooling the number of students with myopia increases, and its degree often increases. By the time they reach adulthood, approximately 1/5 of schoolchildren have their choice of profession limited to one degree or another due to myopia. The progression of myopia can lead to severe irreversible changes in the eye and significant vision loss.

E. S. Avetisov (1975) identifies three main links in the mechanism of myopia development:

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

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

With weakened accommodative ability, increased visual work at close range becomes an unbearable load for the eyes. In these cases, the body is forced to change the optical system of the eyes in such a way as to adapt it to work at close range without the strain of accommodation. This is achieved mainly by lengthening the anterior-posterior axis of the eye during its growth and the formation of refraction. Unfavorable hygienic conditions for visual work affect the development of myopia only to the extent that they complicate accommodation and encourage the eyes to move too close to the object of visual work. With this mechanism of development, myopia usually does not exceed 3.0 diopters.

Weakness of the accommodation apparatus may be a consequence of congenital morphological inferiority or insufficient training of the ciliary muscle or the impact of general disorders and diseases of the body. Insufficient blood supply to the ciliary muscle is also a reason for weakening accommodation. A decrease in its performance leads to an even greater deterioration in the hemodynamics of the eye. It is well known that muscle activity is a powerful activator of blood circulation.

Both autosomal dominant and autosomal recessive types of inheritance of myopia are possible. The frequency of these types of inheritance varies significantly. The second type is especially common in isolates characterized by a high percentage of consanguineous marriages. With an autosomal dominant type of inheritance, myopia occurs at a later age, has a more favorable course and, as a rule, does not reach high degrees. Myopia inherited by an autosomal recessive type is characterized by phenotypic polymorphism, earlier onset, a greater tendency to progression 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 weakens due to a disruption of fibrillogenesis, which may be congenital or arise as a result of general diseases of the body and endocrine shifts, conditions are created for an inadequate response to the stimulus for growth of the eyeball, as well as for its gradual stretching under the influence of intraocular pressure. Intraocular pressure itself (even elevated) in the absence of weakness of the sclera is not capable of leading to stretching of the eyeball, and it is not only, and perhaps not so much, static intraocular pressure that is important, as dynamic intraocular pressure, i.e. "disturbances" of the fluid of the eye during movements of the body or head. When walking or performing any work processes related to visual control, these movements are performed mainly in the anterior-posterior direction. Since there is an obstacle in the anterior part of the eye in the form of an "accommodative" ring, the intraocular fluid during "disturbances" mainly affects the back wall of the eye. Furthermore, as soon as the posterior pole of the eye assumes a more convex shape, in accordance with the laws of hydrodynamics, it becomes the place of least resistance.

Excessive elongation of the eyeball has a negative effect primarily on the choroid and retina. These tissues, being more differentiated, have less plastic capacity than the sclera. There is a physiological limit to their growth, beyond which changes occur in the form of stretching of these membranes and the occurrence of trophic disorders in them, which serve as the basis for the development of complications observed in high degrees of myopia. The occurrence of trophic disorders is also facilitated by reduced hemodynamics of the eye.

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

• congenital myopia that develops as a result of the discrepancy between the anatomical and optical components of refraction, which is the result of a combination of the relatively long axis of the eye with a relatively strong refractive power of its optical media, mainly the crystalline lens. In the absence of weakness of the sclera, such myopia usually does not progress: the elongation of the eye during growth is accompanied by a compensatory decrease in the refractive power of the crystalline lens;
• congenital myopia caused by weakness and increased elasticity of the sclera. Such myopia progresses rapidly and is one of the most unfavorable forms in terms of prognosis;
• congenital myopia with various malformations of the eyeball. In such cases, myopic refraction caused by anatomical and optical discorrelation is combined with various pathological changes and anomalies of eye development (strabismus, nystagmus, colobomas of the eye membranes, subluxation and partial clouding of the lens, partial atrophy of the optic nerve, degenerative changes in the retina, etc.). With weakening of the sclera, such myopia can progress.

As for the shift in refraction towards myopia in people over 60, not all authors note it. The question remains open whether this shift is a natural age-related tendency or whether it is explained by the relatively large number of people among those examined with incipient cataracts, which, as is known, are characterized by swelling of the lens and an increase in its refractive power.

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