accommodation


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accommodation

Physiol the automatic or voluntary adjustment of the shape of the lens of the eye for far or near vision

accommodation

  1. (in race relations) a process in which ethnic groups adjust to each other's existence and coexist without necessarily resolving underlying differences and conflicts (compare ASSIMILATION).
  2. (more generally, e.g. in politics or in domestic life) any individual or group behaviour of the above kind.
  3. (as used by the CHICAGO SCHOOL, e.g. PARK and Burgess, 1921) a fundamental social process, analogous to biological adaptation, by which societies achieve adjustment to 4 (in PIEGET's theory of CHILD DEVELOPMENT) one of the mechanisms by which development from one stage to the next is achieved. See ASSIMILATION AND ACCOMMODATION.

Accommodation

 

a term used in biology and medicine, similar to “adaptation.” The term is traditionally used in the three phrases “accommodation of the eye,” “physiological accommodation,” and “histological accommodation.”

Accommodation of the eye is adaptation of the eye in order to obtain clear vision of objects at various distances. It is achieved by a change in the refractive power of the optical system, which leads to the focusing of the image on the retina. In fish the eye is constructed for close vision, and accommodation is achieved by the rearward displacement of the spherical crystalline lens. In amphibians and reptiles the eye at rest is constructed for distant vision, and accommodation is achieved by the forward movement of the crystalline lens. In birds, mammals, and humans accommodation is achieved by a change in the curvature of the crystalline lens. Accommodation is performed by the accommodation muscles and is possible within certain limits—that is, when the object is at a particular distance from the eye within the field between the points of close and distant vision.

When the intraocular, so-called accommodation muscles contract, the ligaments are relaxed and the crystalline lens suspended on them becomes more protuberant. An increase in the curvature of the crystalline lens leads to a stronger refraction, in consequence of which it becomes possible for the eye to focus the light rays emanating from closely placed objects on the retina and to see them clearly.

The physical factor of crystalline lens elasticity also enters into eye accommodation. In humans the ability of the accommodation muscles to contract and the elasticity of the crystalline lens may change because of a number of conditions. Accommodation is most highly developed in children. With age, elasticity of the crystalline lens diminishes, the ability to see close objects decreases, and so-called senile vision, or presbyopia, develops. Signs of diminution of eye accommodation in persons with normal refraction (emmetropia) appear most commonly between the ages of 40 and 45. When such diminution of eye accommodation occurs, glasses with convex lenses are prescribed for close work (reading and writing) to compensate for the defect. Subsequently, the strength of the eyeglass lenses is gradually increased; by the age of 60 or 70 eye accommodation is usually entirely lost and it is no longer necessary to increase the strength of the eyeglass lenses. Spasm of the accommodation muscles may occur as a result of prolonged eyestrain, bright light, eye trauma, or other factors. Paralysis of these muscles may occur with certain infections and intoxications—for example, syphilis, influenza, diabetes, diphtheria, and botulism. The treatment of spasm or paralysis depends on the cause.

Physiological accommodation, or accommodation of excited muscular or neural tissue, is adaptation to the action of a slowly intensifying stimulus. For example, rapid chilling or a blow may excite an isolated nerve fiber, whereas slow cooling or gradual pressure may not. The same thing is observed with electrical stimulation; with the slow intensification of current, the action potential of a nerve or muscle does not emerge. Such accommodation is associated with active changes in the tissue that raise the threshold of irritability and obstruct the development of excitation.

Histological accommodation, or tissue accommodation, is a change in the forms and relationships of tissue elements (cells) in the process of adaptation to changed conditions. An example of histological accommodation is the transformation of the cubical epithelium of the glomerular capsule into long cylindrical cells when the volume of the glomerulus decreases. However, histological accommodation is often difficult to differentiate from other processes, such as metaplasia and atrophy. The term is therefore merely a formal one.

REFERENCES

Dashevskii, A. I. “Refraktsiia i akkomodatsiia glaza.” In Mnogotomnoe rukovodstvo po glaznym bolezniam, vol. 1, book 1. Edited by V. N. Arkhangel’skii. Moscow, 1962.
Fiziologiia cheloveka. Edited by E. B. Babskii. Moscow, 1966.

M. L. KRASNOV and S. P. LANDAU

accommodation

[ə‚käm·ə′dā·shən]
(control systems)
Any alteration in a robot's motion in response to the robot's environment; it may be active or passive.
(ecology)
A population's location within a habitat.
(mapping)
The limits or range within which a stereo-plotting instrument is capable of operating.
(physiology)
A process in most vertebrates whereby the focal length of the eye is changed by automatic adjustment of the lens to bring images of objects from various distances into focus on the retina.

accommodation

accommodationclick for a larger image
Accommodation: adjustment of eye focus on distant object (left) and close object (right).
i. The ability of the human eye to adjust itself to give sharp images for different object distances. It is the process by which the lens of the eye can be flattened to focus distant points on the retina or made more convex to focus nearby points on the retina.
ii. The limits or range within which a stereo-plotting instrument is capable of operating. For example, a multiplex stereograph can adjust or accommodate for small tilts in the projector, ranging from approximately 10° about the X-axis to 20° about the Y-axis.
References in classic literature ?
The King is admitted into the cell two bundles of straw are shaken down for his accommodation, and he comforts himself that he is now under shelter, and that
On the whole he could perceive that all who were there were people of quality; but with the figure, countenance, and bearing of Don Quixote he was at his wits' end; and all civilities having been exchanged, and the accommodation of the inn inquired into, it was settled, as it had been before settled, that all the women should retire to the garret that has been already mentioned, and that the men should remain outside as if to guard them; the Judge, therefore, was very well pleased to allow his daughter, for such the damsel was, to go with the ladies, which she did very willingly; and with part of the host's narrow bed and half of what the Judge had brought with him, they made a more comfortable arrangement for the night than they had expected.
It is rather from feeling how impossible it is, with all one's efforts, and all one's sacrifices, to make the accommodations on board such as women ought to have.
Not only did the distance to the The Pure Drop, the fully-licensed tavern at the further part of the dispersed village, render its accommodation practically unavailable for dwellers at this end; but the far more serious question, the quality of the liquor, confirmed the prevalent opinion that it was better to drink with Rolliver in a corner of the housetop than with the other landlord in a wide house.
That was why they had come to a boarding-house and had not a nurse for the baby; but they had to have two rooms because they were both used to a good deal of accommodation and they didn't care to be cramped.
We had only the little old shanty and the abandoned church which the good coloured people of the town of Tuskegee had kindly loaned us for the accommodation of the classes.
After I left school, I had the narrowest escape possible of intruding myself into another place of accommodation for distinguished people; in other words, I was very nearly being sent to college.
Not only was the Hand-in-Hand inn crowded, but even the accommodation offered by the nearest town had proved barely sufficient to meet the public demand.
Henry Westwick decided to go to Venice in advance of the rest, to test the accommodation of the new hotel on the opening day.
The Morrow was an English ship with, of course, but little accommodation for passengers, of whom there were only myself, a young woman and her servant, who was a middle-aged negress.
We found accommodation (such as it was) in a river-side inn, used by ship-captains and commercial travelers.
There was just the accommodation in her to sleep a man and a dog.