Age-related changes in accommodation

In patients of preschool and school age against the background of hypermetropic refraction and the "weakness" of the accommodative apparatus, a so-called accommodation spasm can be observed . At the same time there is no complete relaxation of accommodation at distance vision and there is an increase in clinical refraction, that is, there is a myopia, which is called false. Differential diagnosis with true myopia is based on the conduct of medical cycloplegia.

Disorders of accommodation in the elderly are most often due to the age-related changes in the lens: its size, mass, color, shape and, most importantly, consistency, which are mainly related to its growth and biochemical shifts (see the corresponding section).

The gradual decrease in the elasticity of the lens is due to the age-related physiological weakening of the volume of absolute accommodation established by F. C. Donders in 1866. According to his data (Figure 5.8), with emmetropia, the nearest point of clear vision gradually disappears with age with age, which leads to a decrease in the volume of accommodation . At the age of 65-70 years, the nearest and further points of clear vision are combined. This means that the accommodative ability of the eye is completely lost.

The easing of accommodation in the old age is trying to explain not only the crystallization of the lens, but also other causes: degenerative changes in the zinn ligament and a decrease in the contractile capacity of the ciliary muscle. It is established that with the age in the ciliary muscle there are actually changes that can lead to a decrease in its strength. Clear signs of involutional dystrophy of the ciliary muscle appear at the age of 35-40 years. The essence of dystrophic changes in this muscle, which slowly build up, consists in stopping the formation of muscle fibers, replacing them with connective tissue and fatty degeneration. Gradually, the nature of the structure of the muscle is disturbed.

Despite these significant changes in the ciliary muscle, its contractility due to adaptive-compensatory mechanisms is largely preserved, although it is weakening. The relative deficiency of the ciliary muscle is also aggravated by the fact that the muscle has to strain more because of a decrease in the elasticity of the lens to ensure the same degree of curvature. The possibility of secondary atrophic changes in the ciliary muscle is also not excluded due to its inadequate activity in the senile age.

Thus, the weakening of the contractile ability of the ciliary muscle plays a certain role in the age-related decrease in the volume of accommodation. However, the main reasons for this are undoubtedly the condensation of the lens material and a reduction in its elasticity.

At the heart of the development of presbyopia lies the process of reducing the volume of accommodation that occurs throughout life. Presbyopia occurs only in the elderly, when the removal of the nearest point of clear vision from the eye is already significant and this point approaches the average working distance (approximately 33 cm).

The term "presbyopia" (from the Greek presbys - the old man, opsis - vision) - "senile vision" - does not reflect the essence of the process and is a broader, collective concept. The term "senile hyperopia" can not be considered successful, since presbyopia differs significantly from hypermetropia in the mechanism of origin and clinical manifestations.

Presbyopia usually begins to appear in persons with emmetropia at the age of 40-45 years. During this period, the nearest point of clear vision is moved away from the eyes by approximately 23-31 cm, i.e., approaching the average working distance (33 cm). To accurately recognize objects at this distance, an accommodation voltage of approximately 3.0 Dpt is required. Meanwhile, at the age of 45, the average accommodation volume is only 3.2 D (see Figure 5.9). Consequently, it is necessary to spend almost all the amount of accommodation remaining at this age, which causes its excessive stress and rapid fatigue.

With hypermetropia presbyopia occurs earlier, with myopia - later. This is due to the fact that in persons with hypermetropia the nearest point of clear vision is farther from the eyes and its removal beyond the average working distance with age occurs faster than in persons with emmetropia. In people with myopia, pa-turnover, the accommodation area is close to the eye, tense accommodation during work at a close distance is only for near-sightedness less than 3.0 D, so the symptoms of presbyopia with more or less delay may occur only with myopia of low degree. With uncorrected myopia 3.0 dptr and more, presbyopia does not appear.

The main symptom of uncorrected presbyopia is difficulty in treating small objects at close range. Recognition of the latter is somewhat facilitated if they are moved some distance from the eyes. However, with a significant removal of objects of visual work, their angular dimensions decrease and the recognition again deteriorates. The resulting fatigue of the ciliary muscle, due to its excessive strain, can lead to visual fatigue.

Anything that causes at least a short-term removal of the nearest point of clear vision from the eyes and worsens the visibility of objects of visual work, contributes to an earlier manifestation of presbyopia and greater manifestation of its symptoms. In this regard, with other things being equal, presbyopia occurs earlier in individuals whose household or professional activity is related to the examination of small objects. The less the contrast of objects with the background, the stronger this factor. Difficulties in visual work at close range in individuals with presbyopia increase with reduced illumination due to a certain distance from the eyes of the nearest point of clear vision. For the same reason, the manifestations of presbyopia are enhanced by visual fatigue.

It is also noted that with the beginning of cataract manifestations of presbyopia may occur later or weaken if presbyopia already occurs. On the one hand, this is explained by a certain increase in the accommodation volume due to the hydration of the lens substance, which prevents the reduction of its elasticity, on the other hand, by a slight shift in clinical refraction toward the myopia and the approach of a further point of clear vision to the eye. Thus, improvement of vision in presbyopia can serve as an early sign of cataracts beginning. The principles of correction of presbyopia will be described below.

[1], [2], [3], [4], [5], [6]