dark adaptation

adaptation /ad·ap·ta·tion/ (ad″ap-ta´shun)

1. the adjustment of an organism to its environment, or the process by which it enhances such fitness.

2. the normal adjustment of the eye to variations in intensity of light.

3. the decline in the frequency of firing of a neuron, particularly of a receptor, under conditions of constant stimulation.

4. in dentistry, (a) the proper fitting of a denture, (b) the degree of proximity and interlocking of restorative material to a tooth preparation, (c) the exact adjustment of bands to teeth.

5. in microbiology, the adjustment of bacterial physiology to a new environment.

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color adaptation 

1. changes in visual perception of color with prolonged stimulation.

2. adjustment of vision to degree of brightness or color tone of illumination.

dark adaptation  adaptation of the eye to vision in the dark or in reduced illumination.

genetic adaptation  the natural selection of the progeny of a mutant better adapted to a new environment.

light adaptation  adaptation of the eye to vision in the sunlight or in bright illumination (photopia), with reduction in the concentration of the photosensitive pigments of the eye.

phenotypic adaptation  a change in the properties of an organism in response to genetic mutation or to a change in the environment.

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dark adaptation (därk)

n.

The adjustment of the eye under reduced illumination, in which sensitivity to light is greatly increased. Also called scotopic adaptation.

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dark adaptation,

a normal increase in sensitivity of the retinal rod cells of the eye to detect any light that may be available for vision in a dimly lighted environment. The process is accompanied by an adjustment of the pupils to allow more light to enter the eyes.

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adaptation

1. adjustment of the pupil to light, constricting with increased light intensity, dilating with decreased intensity.

2. any anatomical, physiological, developmental or behavioral adjustment to the environment of an organism which enhances its chances of leaving descendants. The ability of animals to adapt to a limited supply of drinking water and to high or low environmental temperatures is an important aspect of animal husbandry. The selection of animals which are capable of a high level of such adaptation has made it possible to improve the productivity of herds and flocks in some countries. See also general adaptation syndrome.

3. the process by which organisms are modified so as to improve their chances of survival in an environment.

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dark adaptation

adaptation of the eye to vision in the dark or in reduced illumination.

light adaptation

adaptation of the eye to vision in sunlight or in bright illumination (photopia), with reduction in the concentration of the photosensitive pigments of the eye.

negative adaptation

see habituation.

adaptation rate

the rate at which afferent sensory receptors discharge into their afferent axons. The rates differ between different types of receptors. For example, there are slow adaptors which signal the more persistent changes such as steady pressure. See also receptor adaptation (below).

receptor adaptation

sensory receptors vary in their individual response to stimuli, the response declining after an initial period of rapid response. The rate at which different kinds of receptors change these responses is the adaptation rate (see above).