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an encircling region or area; by extension, any area with specific characteristics or boundary.
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 and 70°F) with a humidity of 30 to 55 per cent.
epileptogenic zone an area, stimulation of which may provoke an epileptic seizure.
erogenous zone (erotogenic zone) in psychoanalytic theory, an area of the body through which the libido expresses itself and which is therefore susceptible to erotic excitation upon stimulation; the primary sites are the oral, anal, and genital regions, but the other body orifices, breasts, and skin are also included.
zone of partial preservation in spinal cord injury, an area of only partial damage that may include up to three consecutive spinal segments caudal to the level of the injury.
pupillary zone the inner of the two regions into which the anterior surface of the iris is divided by the collarette.
transition zone (transitional zone) any anatomical region that marks the point at which the constituents of a structure change from one type to another; for example, the circle in the equator of the ocular lens in which epithelial fibers are developed into lens fibers, or the zone (anocutaneous line) that marks the junction of stratified squamous epithelium with columnar epithelium.
the outer wider zone of the anterior surface of the iris, separated from the pupillary zone by the collarette.
Synonym(s): zona ciliaris
cil·i·ar·y zone(sil'ē-ar-ē zōn)
The outer, wider zone of the anterior surface of the iris, separated from the pupillary zone by the collarette.
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|
|injection||conjunctival||ciliary||conjunctival and ciliary|
|pupil||normal||contracted||semi-dilated and fixed|
|intraocular pressure||normal||normal or low, occasionally increased||high|
|anterior chamber||normal depth||normal depth, aqueous flare||shallow|
|view of fundus||clear||misty||almost invisible|
|pain||irritation||moderate to servere||very severe and radiating|
|lacrimation||watery, purulent or mucopurulent||watery||watery|
|vision||normal||slightly reduced||much reduced, haloes|
|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.|