Ability of eyes subjects to see identical at different distance – and there is an eye akkomadition. That is, ability of eyes to adapt for different distance. Process is absolutely automatic, not dependent on the person and is made under the influence of an unconditioned reflex.
Akkomadition has the structure, versions and the mechanism of action put by the nature. Is an important component of optical system of eyes. Akkomadition gives in to age therefore with a tide of life ability to see close or far decreases. In a type of it, use of the special exercise machine and performance of the strengthening exercises for eyes will be not superfluous.
Accommodation of an eye: structure and functions, types and mechanism of action
Besides, fibers of a tsinnovy sheaf and a tsiliarny muscle are a part of the device. The last components hold a crystalline lens and influence its situation. Cyanic sheaf and a tsiliarny muscle provide an akkomadition of eyes.
Collaboration of all of components of the device provides ability of optical system of eyes to create accurate images of the objects and subjects which are on different removal from eyes. At the time of examining of the most remote objects and subjects, parallel beams get to an eye. It is called as an akkomadition on infinity.
We will note that a dynamic refraction – not eternal. By means of a ring muscle, there is an increase in optical power of an eye, at most on 12dioptry. Long examining of subjects, irrespective of their removal – an eye is tired of visual body, and the muscle – relaxes. As a result the picture blurs.
Functions of accommodation of eyes
The dynamic refraction carries out such functions:
- changes curvature of a crystalline lens
- focuses the image on a retina
- regulates amount of light by means of a mioz and a midriaz (narrowing and expansion of a pupil)
Types of an akkomadition
- The absolute
- The relative
- The reflex
- The proximal
- The tonic
- The absolute akkomadition of eyes represents change of curvature of a crystalline lens only of one eye. Thus the second eye doesn't participate in this process.
- The relative akkomadition consists that curvature of a crystalline lens changes at both eyes.
- The reflex akkomadition is an automatic fixing of a refraction for ensuring continued support of clearness of the visible image.
- The proximal akkomadition – this type of a dynamic refraction comes into effect when the object comes nearer to looking, more than on three meters before its recognition.
- Vergentny accommodation is a total number of accommodations of both eyes in at one time.
- The tonic akkomadition – shows a condition of a refraction during absence of akkomaditsionny incentive.
All these types of a dynamic refraction explain its operation in each separate case.
Mechanism of an akkomadition of eyes
The mechanism of action of a dynamic refraction is constructed on effect of fibers of a tsinnovy sheaf, tsiliarny muscle which mainly I influence a crystalline lens form.
There is a set of the theories explaining and describing the mechanism of action of adaptation of eyes to remoteness of the image. The most substantial and correct Helmholtz's version is considered.
So, according to this popular theory when the visual body looks afar, the tsiliarny muscle is in the weakened state. Tsinnova a sheaf, in turn, is in the tense state. We will remind, these sheaves connect internal part of a tsiliarny body and the equatorial area of a crystalline lens. Such structure provides camber of a form of a crystalline lens.
In the course of a dynamic refraction circular fibers of a tsiliarny muscle – are reduced therefore, a tsinnova the linking of fibers – relaxes, and the crystalline lens becomes convex, changing refraction of the getting light in a pupil and transferred to a retina.
Akkomadition starts working with that moment when the person starts reading, for example, from short (distant) distance.
This activity of an eye by optical system by parasympathetic department of vegetative nervous system is regulated. This department of system controls reductions of a tsiliarny muscle.
Also in the course of an akkomadition also the sympathetic part of the nervous system participates. Mainly it carries out trophic function and slows down activity of a tsiliarny muscle a little.