- The opening of the iris. The pupil may appear to open (dilate) and close (constrict) but it is really the iris that is the prime mover; the pupil is merely the absence of iris. The pupil determines how much light is let into the eye. Both pupils are usually of equal size. If they are not, that is termed anisocoria (from "a-", not + "iso", equal + "kore", pupil = not equal pupils). Aside from the pupil and iris, the eye has a number of other components. These components include the cornea, lens, retina, macula, optic nerve and vitreous. The cornea is the clear front window of the eye that transmits and focuses light into the eye. The lens is the transparent structure inside the eye that focuses light rays onto the retina. The retina is the nerve layer that lines the back of the eye, senses light and creates impulses that travel through the optic nerve to the brain. The macula is a small area in the retina that contains special light-sensitive cells and allows us to see fine details clearly. The optic nerve is the nerve that connects the eye to the brain and carries the impulses formed by the retina to the visual cortex of the brain. The vitreous humor is a clear, jelly-like substance that fills the middle of the eye.
* * *The circular orifice in the center of the iris, through which the light rays enter the eye. SYN: pupilla [TA]. [L. pupilla]- amaurotic p. p. in an eye that is blind because of ocular or optic nerve disease; this p. will not contract to light except when the normal fellow eye is stimulated with light.- Argyll Robertson p. a form of reflex iridoplegia characterized by miosis, irregular shape, and a loss of the direct and consensual pupillary reflex to light, with normal pupillary constriction to a near vision effort (light-near dissociation); often present in tabetic neurosyphilis. SYN: Robertson p..- artificial p. an opening made by excision of a portion of the iris in order to improve the vision in cases of central opacity of the cornea or lens.- catatonic p. transient pupillary dilation with absence of pupillary reaction to light and convergence.- fixed p. a stationary p. unresponsive to all stimuli.- Gunn p. SYN: Marcus Gunn p..- Horner p. constricted p. due to impairment of sympathetic nerve innervation of the dilator muscle of the p.. SEE ALSO: Horner syndrome.- Hutchinson p. dilation of the p. on the side of the lesion as part of a third nerve palsy; often due to herniation of the uncus of the temporal lobe through the tentorial notch.- keyhole p. a p. with a coloboma.- Marcus Gunn p. relative afferent pupillary defect. SYN: Gunn p..- paradoxical p. paradoxical pupillary reflex.- pinhole p. an extremely constricted p..- Robertson p. SYN: Argyll Robertson p..- seclusion of p. (se-kloo′zhun) the condition resulting from posterior annular synechia, in which the iris is bound down throughout the entire pupillary margin, but the p. is not occluded. SYN: exclusion of p..- tadpole-shaped p. an intermittent, brief distortion and dilation of a p. that draws one part of the iris into a peak so that the p. resembles a tadpole; a temporary, benign condition associated with migraine that may leave the patient with Horner syndrome.- tonic p. a general term for a p. with delayed, slow, long-lasting contractions to light and to a near vision effort, often with light-near dissociation; due to denervation and aberrant reinnervation of the iris sphincter; seen in various autonomic neuropathies and in Adie syndrome.
* * *pu·pil 'pyü-pəl n the contractile usu. round aperture in the iris of the eye
* * *n.the circular opening in the centre of the iris, through which light passes into the lens of the eye.• pupillary adj.
* * *pu·pil (puґpil) [L. pupilla girl] the opening at the center of the iris of the eye, through which light enters the eye; in official terminology, called pupilla. See also iris. pupillary adj
Medical dictionary. 2011.