pupil

The circular orifice in the center of the iris, through which the light rays enter the eye.

Synonym(s): pupilla [TA]

[L. pupilla]

The circular orifice in the center of the iris, through which light rays enter the eye.
Synonym(s): pupilla [TA] .

[L. pupilla]

Mentioned in: Eye Cancer, Eye Examination, Hyperopia, Radial Keratotomy, Uveitis

Aperture within the iris, normally circular, through which light penetrates into the eye. It is located slightly nasally to the centre of the iris. Its diameter can vary from about 2 to 8 mm. It is often slightly smaller in old age. The function of the pupil is to regulate the amount of light admitted into the eye, to optimize the depth of focus and to mitigate ocular aberrations. See acorea; anisocoria; corectopia; dicoria; dyscoria; hippus; iridectomy; microcoria; miosis; dilator pupillae muscle; sphincter pupillae muscle; mydriasis; Edinger-Westphal nucleus; polycoria; polyopia; pupil light reflex.
Adie's pupil A pupil in which the reactions to light, direct or consensual, are almost abolished, with a reaction occurring only after prolonged exposure to light or dark. The reaction of the pupil to a near target is also delayed and slow. The condition is usually unilateral, with the affected pupil being the larger of the two (anisocoria). It may be due to a disease of, or injury to, the ciliary ganglion or to the short ciliary nerves. Other causes include temporal arteritis in elderly patients, syphilis or diabetes. Syn. myotonic pupil; pupillotonia; tonic pupil (some authors use this last term when the cause is known and Adie's pupil when the cause is unidentified). See efferent pupillary defect; Adie's syndrome; pupil light reflex.
amaurotic pupil Miotic pupil that does not react to direct and consensual ipsilateral light stimulation, but does react consensually to contralateral stimulation. It is most often noted in cases of severe optic nerve dysfunction or retinal disease.
apparent pupil See entrance pupil of the eye.
Argyll Robertson pupil Pupil that reacts when the eye accommodates and converges but fails to react directly and consensually to light. The condition is bilateral, the pupils are small and usually unequal. It is usually a sign of neurosyphilis. See iridoplegia; tabes dorsalis.
artificial pupil 1. Pupil made by iridectomy. 2. A circular aperture made in a diaphragm which can be mounted in front of the eye to provide a constant and smaller pupil size. It is used in research but also as a clinical test. See pinhole disc.
pupil block See pupillary block.
pupil constriction See miosis; pupil light reflex.
pupil dilatation See mydriatic; pupil light reflex.
ectopic pupil See corectopia.
entrance pupil of the eye This is the image of the iris aperture formed by the cornea. It is what one sees when one looks at an eye. It is some 13% larger than the real pupil and located slightly in front of it. Syn. apparent pupil (Fig. P23).
exit pupil of the eye This is the image of the iris aperture formed by the crystalline lens. It is slightly larger (,3%) than the real pupil and situated slightly behind it (Fig. P23).
Horner's pupil See syndrome, Horner's.
Hutchinson's pupil A pupil that is dilated and completely inactive to all stimuli. It is associated with lesions of the central nervous system, as may occur in head injury.
keyhole pupil A pupil shaped like a keyhole due to iridectomy in which a section of the iris extending from the pupillary margin to the periphery has been excised, or due to coloboma or trauma to the iris.
pupil light reflex See pupil light reflex.
Marcus Gunn pupil A defect of the pupillary reflex characterized by a smaller constriction of both pupils when the affected eye is stimulated by light as compared to that occurring when the normal eye is stimulated. It is easier, however, to observe this phenomenon when swinging a light from one eye to the other in a darkened room while the subject is fixating a distant object (this is called the swinging flashlight test) (Fig. P24). Stimulation of the normal eye will cause constriction of both pupils whereas rapid stimulation of the affected eye will lead to a small dilatation (a paradoxical reaction, sometimes referred to as pupillary escape). This condition is due to a lesion in one retina or in one of the optic nerves, optic chiasma, optic tract, or the pretectal olivary nucleus that affects the afferent pupillary pathway. It is often the result of central or branch retinal or vein occlusion, extensive retinal detachment, retrobulbar optic neuritis, compressive optic neuropathy, or optic tract lesion, etc. Syn. relative afferent pupillary defect (RAPD), if the magnitude of the effect is partial; afferent pupillary defect (APD), if it is complete.
myotonic pupil See Adie's pupil.
pupil reflex See pupil reflex.
tonic pupil See Adie's pupil.
white pupil See leukocoria.

Table P11 Examples of pupil abnormality
defect		appearance		light response*		consensual light response*		near response
Adie's pupil		large		impaired		impaired		slow
Argyll Robertson		both pupils small, unequal + irregular		almost abolished		almost abolished		normal
blindness in one eye		normal		abolished		abolished		normal
Horner's syndrome		small + ptosis		normal		normal		normal
Hutchinson's pupil		large		abolished		abolished		abolished
optic neuritis		normal/large		impaired		impaired		normal
3rd nerve paralysis†		large + ptosis		abolished		abolished		abolished
*To stimulation of the affected eye.†When caused by an aneurysm of the posterior communicating artery.

Circular orifice in center of iris, through which light rays enter eye.

[L. pupilla]