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 ?
Sorry I can't accommodate you with red-hot shot, Tom Platt; but I guess we'll come aout all right on wind 'fore we see Eastern Point.
The prince's subjects are now pretty numerously employed about the station-house, some in taking care of the baggage, others in collecting fuel, feeding the engines, and such congenial occupations; and I can conscientiously affirm that persons more attentive to their business, more willing to accommodate, or more generally agreeable to the passengers, are not to be found on any railroad.
The forms of those bodies are accurately such as, within a given surface, to include the greatest possible amount of matter; -- while the surfaces themselves are so disposed as to accommodate a denser population than could be accommodated on the same surfaces otherwise arranged.
They were only concerned that the house could accommodate no more; and yet perhaps, by "putting the children away in the maid's room, or swinging a cot somewhere," they could hardly bear to think of not finding room for two or three besides, supposing they might wish to stay; though, with regard to any attendance on Miss Musgrove, there need not be the least uneasiness in leaving her to Mrs Harville's care entirely.
Not at all,' said I, 'I shall be very happy to accommodate myself to your wishes.
Contrariwise, certain Laodiceans, and lukewarm persons, think they may accommodate points of religion, by middle way, and taking part of both, and witty reconcilements; as if they would make an arbitrament between God and man.
I have every hope that the company may accommodate you.
You must accommodate the visit to the demands upon my time.
The passengers soon learned to accommodate themselves to their new circumstances, and life in the ship became nearly as systematically monotonous as the routine of a barrack.
Their ears were pierced and distended to accommodate wooden plugs and sticks, pipes, and all manner of barbaric ornaments.
Now he considered that it would be neither an easy nor a necessary work to make himself such a house as would accommodate him.
The Lord Advocate (speaking on the other side) was happy to be able to accommodate his learned brother in this matter.