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see eyeeye,
organ of vision and light perception. In humans the eye is of the camera type, with an iris diaphragm and variable focusing, or accommodation. Other types of eye are the simple eye, found in many invertebrates, and the compound eye, found in insects and many other
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the opening in the iris through which light rays enter the eye.

The dimensions of the pupil change according to the amount of light present: the pupil dilates in darkness, under emotional excitement and painful sensations, or with the injection of atropine or adrenalin into the body; it contracts in bright light. Change in the dimensions of the pupil is regulated by fibers of the autonomic nervous system and is accomplished by means of two smooth muscles located in the iris—the sphincter, which contracts the pupil, and the dilator, which expands it. In higher vertebrates, changes in the dimensions of the pupil are produced reflexively by the effect of light on the retina of the eye; in lower vertebrates, these changes are produced by the direct action of light on contrac-tile formations in the pupil. The pupil is usually round or slitlike; in some fish (for example, in a number of sharks, rays, and flounder) and mammals (for example, in sperm whales and dolphins) a projection of the iris, suspended from the superior edge of the pupil, can cover the pupil completely in the presence of intense illumination. In man the pupil is round; its diameter may change from 1.1 mm to 8 mm. Changes in the shape, dimensions, and speed of reaction of the pupil (so-called pupillary reflexes) are of diagnostic significance in eye diseases.



The contractile opening in the iris of the vertebrate eye.


1. a student who is taught by a teacher, esp a young student
2. Civil and Scots law a boy under 14 or a girl under 12 who is in the care of a guardian


the dark circular aperture at the centre of the iris of the eye, through which light enters
References in periodicals archive ?
Distante, "Unsupervised eye pupil localization through differential geometry and local self-similarity matching," PLoS ONE, vol.
"Only one child is still showing signs of confusion with dilated eye pupils," added Dr Mate.
He further discusses interesting applications that have been conceptualised, including tracking students' eye pupils to access the emotional profile of students in real time.
For optimum performance and to ensure that all of the captured light enters the observer's eyes, the exit pupil of the binoculars should be smaller than your fully dark-adapted eye pupils. As you age your pupils dilate less, and while the pupils of someone in their twenties may increase to over 7mm, those of someone in the sixties may struggle to reach 5mm and for people in their seventies it can reduce to 3mm.