iris (redirected from papillary zone)

iris (i´ris) pl. i´rides   [Gr.] the circular pigmented membrane behind the cornea, perforated by the pupil.

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i·ris (rs)

n. pl. i·ris·es or i·ri·des (r-dz, r-)

The round pigmented contractile membrane of the eye that is perforated in the center by the pupil, forms the front part of the vascular tunic, and is attached on the margin to the ciliary body.

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iri·dal (r-dl, r-), i·ridi·al (-rd-l, -rd-), i·ridi·an adj.

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Iris (plural, irides)

The circular pigmented membrane behind the cornea of the eye that gives the eye its color. The iris surrounds a central opening called the pupil.

Mentioned in: Eye Cancer, Eye Examination, Glaucoma, Hyperopia, Radial Keratotomy, Retinal Vein Occlusion, Trabeculectomy, Uveitis, Vitiligo

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iris

[ī′ris]

Etymology: Gk, rainbow

an annular, colored membrane shaped like a disc, suspended in aqueous humor between the cornea and the crystalline lens of the eye and enclosing a circular pupil. Smooth muscle fibers of the iris contract and relax to allow more or less light to enter the eye through the pupil. The periphery of the iris is continuous with the ciliary body and is connected to the cornea by the pectinate ligament. The iris divides the space between the lens and the cornea into an anterior and a posterior chamber. The involuntary muscle of the iris is composed of circular fibers and radiating fibers. Dark pigment cells under the translucent tissue of the iris are variously arranged in different people to produce different colored irises. The pigment is absent in albinos. In blue eyes the pigment cells are confined to the posterior surface of the iris, but in gray eyes, brown eyes, and black eyes the pigment cells appear in the anterior layer of epithelium and in the stroma. See also dilator pupillae, sphincter pupillae. iridic, adj.

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iris,

n a circular, contractile disc suspended in aqueous humor between the cornea and the crystalline lens of the eye and perforated by a circular pupil. It regulates the amount of light passing into the chambers of the eye.

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Iris

a European plant genus of the Iridaceae family; contain cardiac glycosides. Cause sudden death, diarrhea. Includes I. foetidissima (wild iris), I. germanica (cultivated iris), I. missouriensis, I. pseudacorus (yellow flag), I. versicolor.

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iris

The anterior part of the vascular tunic of the eye, which is situated in front of the crystalline lens and behind the cornea. It has the shape of a circular membrane with a perforation in the centre (the pupil) and is attached peripherally to the ciliary body. The iris forms a curtain dividing the space between the cornea and the lens into the anterior and posterior chambers of the eye. The anterior surface of the iris is divided into two portions: the largest peripheral ciliary zone and the inner pupillary zone. The two zones are separated by a zigzag line, the collarette. The iris consists of four layers which are, starting in the front: (1) the layer of fibrocytes and melanocytes; (2) the stroma in which are embedded the following structures: (a) the sphincter pupillae muscle which constricts the pupil and is supplied mainly by parasympathetic fibres via the third cranial nerve, (b) the vessels which form the bulk of the iris, and (c) the pigment cells; (3) the posterior membrane consisting of plain muscle fibres which constitute the dilator muscle which is supplied mainly by sympathetic motor fibres, via the long ciliary nerves; (4) the posterior epithelium which is highly pigmented.Sensory fibres from the iris are contained in the nasociliary branch of the ophthalmic nerve. The blood supply is provided by the ciliary arteries. The colour of the iris is blue in babies belonging to the white races and changes colour after a few months of life as pigment is deposited in the anterior limiting layer and the stroma. Iris colour is inherited; brown as a dominant trait and blue as a recessive trait. Iris patterns are unique for each individual and can be used as a type of identification. The function of the iris and pupil is to regulate the amount of light admitted into the eye, to optimize the depth of focus and to mitigate ocular aberrations.See cell, clump; corectopia; Fig. C 13; Fuchs, crypts of; heterochromia; inheritance; iridectomy; iridodialysis; iridology; iritis; melanin; membrane, pupillary; polycoria; reflex, pupil light.

Table I6 Differential diagnosis* between acute conjunctivitis, acute iritis and angle-closure glaucoma
		acute conjunctivitis		acute iritis (anterior uveitis)		angle-closure glaucoma
signs
injection		conjunctival		ciliary		conjunctival and ciliary
pupil		normal		contracted		semi-dilated and fixed
intraocular pressure		normal		normal or low, occasionally increased		high
cornea		normal		KP		Oedematous
anterior chamber		normal depth		normal depth, aqueous flare		shallow
iris		normal		faded		faded
view of fundus		clear		misty		almost invisible
symptoms
pain		irritation		moderate to servere		very severe and radiating
photophobia		slight		marked		slight
lacrimation		watery, purulent or mucopurulent		watery		watery
vision		normal		slightly reduced		much reduced, haloes
onset		gradual		rapid		sudden
systemic complications		none		malaise or fever		nausea and vomiting
*This is a guide, as individual cases vary according to the cause and severity of the disease.

Fig. C13  Coloboma of the iris