ciliary zone

zone (zōn) an encircling region or area; by extension, any area with specific characteristics or boundary.zo´nal

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ciliary zone  the outer of the two regions into which the anterior surface of the iris is divided by the collarette.

comfort zone  an environmental temperature between 13° and 21°C (55°–70°F) with a humidity of 30 to 55 per cent.

epileptogenic zone  see under focus.

erogenous zone , erotogenic zone an area of the body whose stimulation produces erotic excitation.

inner zone of renal medulla  the part of the medulla farthest in from the cortex, containing ascending and descending limbs of the thin tubule as well as the inner part of the medullary collecting duct.

Lissauer's marginal zone  a bridge of white substance between the apex of the posterior horn and the periphery of the spinal cord.

outer zone of renal medulla  the part of the medulla nearest to the cortex; containing the medullary part of the distal straight tubule as well as the outer part of the medullary collecting duct.

zone of partial preservation  in spinal cord injury, a region where there may be only partial damage to nerves, including one to three spinal segments below the level of the injury.

pellucid zone  zona pellucida.

pupillary zone  the inner of the two regions into which the anterior surface of the iris is divided by the collarette.

transitional zone  any anatomical region that marks the point at which the constituents of a structure change from one type to another.

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ciliary zone

n.

The outer area of the anterior surface of the iris, adjacent to the pupillary zone.

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ciliary zone,

an outer circular area on the anterior surface of the iris, separated from the inner circular area by the angular line. The ciliary zone contains the stroma of the iris. Also called zonula ciliaris.

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zone

an encircling region or area; by extension, any area with specific characteristics or boundary. See also zona.

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autonomous innervation zone

areas of innervation supplied by a single nerve, as for example the patch of skin on the medial side of the horse fore pastern which is supplied solely by the median nerve; used to assess the integrity of individual nerves.

ciliary zone

the outer of the two regions into which the anterior surface of the iris is divided by the angular line.

comfort zone

an environmental temperature between 55° and 70° F (13° and 21° C) with a humidity of 30 to 55%.

epileptogenic zone

an area, stimulation of which may provoke an epileptic seizure.

zone of inhibition

the area without bacterial growth surrounding an antimicrobial-impregnated disk in an antimicrobial sensitivity test.

provisional calcification zone

in developing bone longitudinal tubes of mineralized matrix which surround hypertrophic chondrocytes.

transitional zone

the circle in the equator of the lens of the eye in which epithelial fibers are developed into lens fibers.

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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