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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 ?
Distribution Cases according to Presence of relative Afferent Pupillary Defect No.
In our patient, the presence of relative afferent pupillary defect in the right eye, impaired color vision in both eyes, and significantly prolonged p100 latency on pVEP were considered evidence of previous optic neuritis attack and optic nerve demyelination.
Presence of lid oedema, restricted ocular movements, proptosis, loss of vision and relative afferent pupillary defect were looked for.
Examination also revealed an afferent pupillary defect of the right eye and right lateral rectus muscle palsy (figure 1).
Asymmetric glaucoma is also detected in a patient with relative afferent pupillary defect (RAPD) or asymmetric optic nerve cupping without an RAPD.
The swinging flashlight test is performed in order to detect relative afferent pupillary defect (RAPD).
The left eye also exhibited a large central scotoma, dyschromatopsia, and a left afferent pupillary defect.
Anterior segment evaluation revealed relative afferent pupillary defect.
c Assessment for a relative afferent pupillary defect and fundus fluorescein angiography
Relative afferent pupillary defect, prolonged VEP latency, and low amplitudes are useful for the evaluation of the cases.
His visual acuity was 6/6 right and 6/5 left, he had no relative afferent pupillary defect, and his ocular movements were normal.