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Eye accommodation

Accommodation of the eye is the ability to clearly see objects at different distances from the eye. The physiological mechanism of accommodation of the eye is that when the fibers of the ciliary muscle of the eye are contracted, the zin ligament is relaxed, with the help of which the lens is attached to the ciliary body (see the Eye ). At the same time, the tension of the lens bag decreases, and due to elastic properties it becomes more convex. Relaxation of the ciliary muscle leads to flattening of the lens. In fig. 1 shows the scheme of accommodation of the eye (the solid line - the position of the lens at rest, the dotted - with accommodation). The innervation of the ciliary muscle is carried out by the oculomotor and sympathetic nerves.

eye accommodation scheme
Fig. 1. Accommodation scheme of the eye.

dependence of the volume of accommodation on age
Fig. 2. The dependence of the volume of accommodation on age.
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Accommodation of the eye is possible within the limits of the nearest and further points of clear vision. The first is determined by the smallest distance at which it is possible to read the fine print; the second is the greatest distance at which the object is clearly visible in the absence of accommodation of the eye. The position of the further point of clear vision depends on the refraction of the eye (see). The increase in the refractive power of the optical system of the eye, achieved at the maximum voltage of accommodation of the eye, is called the volume, or force, of the accommodation of the eye.

Pathological changes include spasm , paralysis, and paresis of accommodation of the eye. A spasm usually occurs in young people with prolonged tension in the accommodation of the eye, trauma, the action of very bright light on the eye. Accommodation spasm is manifested by myopia . Paralysis and paresis of accommodation of the eye can be of central origin and caused by infections and intoxications. Peripheral paralysis of accommodation of the eye is observed with eye injuries, ingestion of atropine preparations, and instillation of the pupil in the conjunctival sac during instillation into the conjunctival sac. The paralysis of accommodation of the eye is characterized by the inability to distinguish the fine print at close range. For the treatment of spasm and paralysis of accommodation of the eyes of the patients are subject to referral to the doctor- oculist.

Age years Accommodation Size (D)
ten 14.0
15 12.0
20 10.0
25 8.0
thirty 7.0
35 5.5
40 4.5
45 3.5
50 2.5
55 one
60 1.0
65 0.5
70 0.25
75 0

Accommodation of the eye (lat. Accomodatio - device) is the property of the eye to change the refractive power to adapt to the perception of objects that are at different distances from it. The mechanism of accommodation of the eye is as follows: upon contraction of the fibers of the accommodative muscle embedded in the ciliary body, the ligament of the Zin ligament is relaxed, by means of which the lens is suspended from the ciliary body; as a result, the lens with elastic properties acquires a more convex shape, and the refractive ability of the eye is enhanced (Fig.). When the accommodative muscle relaxes, the fibers of the Zin ligament stretch, the lens flattens, and the refractive power of the optical system of the eye decreases accordingly. Accommodation of the eye can be carried out within certain limits, depending mainly on the elastic properties of the lens.

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The closest point to the eye, which he is able to see clearly at the maximum voltage of accommodation, is called the nearest point of clear vision; the most distant point, clearly visible in the absence of accommodation of the eye, is called the further point of clear vision. The linear distance between the nearest and further points of clear vision, that is, space, in. the limits of which the eye can clearly see is called the length, or area, of the accommodation of the eye. The change in the refractive power of the eye, which is achieved at the maximum voltage of accommodation, is called the volume (force, amplitude, or width) of accommodation (expressed in diopters). With age, the accommodation of the eye changes as a result of the gradual loss of the elasticity of the lens and the ability to change its shape (curvature). Age-related changes in the volume of accommodation of the eye are shown in the Donders table.

eye accommodation
Accommodation of the eye: 1 - the lens while relaxing accommodation; 2 - the lens at the voltage of accommodation.

The average numbers shown in the table may vary among different individuals, but within relatively small limits. The age-related weakening of accommodation leads to a gradual moving away from the eye of the nearest point of clear vision, deterioration of conditions for viewing closely located objects, to the development of the so-called senile vision - presbyopia (see).

Pathological disorders of accommodation of the eye are spasm and paralysis. Spasm of accommodation of the eye occurs mainly in young people as a result of prolonged strain of accommodation, as well as injuries to the eye and the effect on the eye of a very bright light. Clinically, eye spasm of accommodation is manifested as myopia. The paralysis of the accommodation of the eye is characterized by a loss of the ability to see clearly near. The causes of eye paralysis are mainly infections, intoxication and trauma.