blue-eyed grass

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

i·ris (

n. pl. i·ris·es or i·ri·des (

-d

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.

iri·dal (

-dl,

-), i·ridi·al (

-r

-), i·ridi·an adj.

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

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.

eye [i]

the organ of vision; see also Plates. In the embryo the eye develops as a direct extension of the brain, and thus is a very delicate organ. To protect the eye the bones of the skull are shaped so that an orbital cavity protects the dorsal aspect of each eyeball. In addition, the conjunctival sac covers the front of the eyeball and lines the upper and lower eyelids. Tears from the lacrimal duct constantly wash the eye to remove foreign objects, and the lids and eyelashes help protect the front of the eye.

Structure. The eyeball has three coats. The cornea is the clear transparent layer on the front of the eyeball; it is a continuation of the sclera (the white of the eye), the tough outer coat that helps protect the delicate mechanism of the eye. The choroid is the middle layer and contains blood vessels. The third layer, the retina, contains rods and cones, which are specialized cells that are sensitive to light. Behind the cornea and in front of the lens is the iris, the circular pigmented band around the pupil. The iris works much like the diaphragm in a camera, widening or narrowing the pupil to adjust to different light conditions.

Function. (See also vision.) The refraction or bending of light rays so that they focus on the retina and can thus be transmitted to the optic nerve is accomplished by three structures: the aqueous humor, a watery substance between the cornea and lens; the lens, a crystalline structure just behind the iris; and the vitreous humor, a jelly-like substance filling the space between the lens and the retina. Unlike the lens of a camera, the lens of the eye focuses by a process called accommodation. This means that when the eye sees something in the distance, muscles pull the lens, stretching it until it is thin and almost flat, so that the light rays are only slightly bent as they pass through it. When the object is close, the muscles relax and the elastic lens becomes thicker, bending the light rays and focusing them on the retina.ƒ

Because the eye must function under many different circumstances, there are two types of nerve cells in the retina, with different shapes: the cones and the rods. They cover the full range of adaptation to light, the cones being sensitive in bright light, and the rods in dim light. The cones are responsible for color vision. There are three types of cones, each containing a substance that reacts to light of a different color, one set for red, one for green, and one for violet. These are the primary colors in light, which, when mixed together, give white. White light stimulates all three sets of color cells; any other color stimulates one or two.

The optic nerve, which transmits the nerve impulses from the retina to the visual center of the brain, contains nerve fibers from the many nerve cells in the retina. The small spot where it leaves the retina does not have any light-sensitive cells, and is called the blind spot.

The eyes are situated in the front of the head in such a way that human beings have stereoscopic vision, the ability to judge distances. Because the eyes are set apart, each eye sees farther around an object on its own side than does the other. The brain superimposes the two slightly different images and judges distances from the composite image.

Disorders of the Eye. If the eyeball is too short or too long, the lens focuses the image not on the retina but behind or in front of it. The former condition is called hyperopia (or farsightedness) and the latter myopia (or nearsightedness). An irregularity in the curvature of the cornea or lens can cause the impaired vision of astigmatism. strabismus (or squint or crossed eyes) is usually caused by weakness in muscles that control movement of the eyeball. conjunctivitis is an inflammation of the membrane that covers the front of the eyeball and lines the eyelids. When small pieces of the retina become detached from the underlying layers, the result is a retinal detachment; surgery may be necessary to prevent blindness. presbyopia (usually taking the form of hyperopia) occurs in older persons and develops as the lens loses its elasticity with the passing years. Correction is easily made with properly prescribed eyeglasses.ƒ

Foreign bodies in the eyes are common occurrences. Protective eyewear should be worn by individuals at risk. Cinders, grit, or other foreign bodies are best removed by lifting the eyelid by the lashes. The foreign body will usually remain on the surface of the lid, and can easily be removed. Particles embedded in the eyeball must be removed by a qualified health care professional.

Eyestrain is fatigue of the eyes caused by improper use, uncorrected defects in the vision, or an eye disorder. Symptoms may include aching or pains in the eyes, or a hot, scratchy feeling in the eyelids. Headache, blurring or dimness of vision, and sometimes dizziness or nausea may also occur.

Anatomic features of the eye. From Ignatavicius and Workman, 2002.

artificial eye a glass or plastic prosthesis inserted in the eye socket to replace the eyeball; most are designed to be worn day and night. When patients become debilitated and unable to care for such a prosthesis, they must depend on members of the health care team to give proper care according to the chosen preferred routine.ƒ

Cleaning of a prosthetic eye is similar in principle to care of dentures; both are handled with care to avoid damage and are cleansed according to good hygienic principles. The prosthesis is removed while the patient is lying down so that it falls into the hand and is not likely to be dropped and broken. It is removed by depressing the lower eyelid, allowing the prosthesis to slide out and down. Mild soap and water are most often used for cleansing the prosthesis. Alcohol or other chemicals can damage prostheses made of plastic. If it is not replaced in the socket immediately after cleansing, it is stored in water or contact lens soaking solution. Insertion of the prosthesis is done by lifting the upper eyelid with the thumb or forefinger and placing its notched edge toward the nose. It is placed as far as possible under the upper lid and then the lower lid is depressed to allow it to slip into place. The process can be made easier by first moistening the prosthesis with water. If it is necessary to wipe the eye area of a patient wearing a prosthesis, one should gently wipe toward the nose in order not to dislodge the prosthesis.

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

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Adie's pupil aniridia anterior synechia Axenfeld's anomaly ciliary margin ciliary zone collarette coloboma crypt of iris flag iris glaucoma heterochromia heterochromia iridis iridectomy iridemia irides iridocorneal endothelial syndrome iridocyclitis iridology			blue slime disease Blue Spell blue spot blue spot disease blue squill Blue Suit Blue Tabs Blue Tag blue tick Blue Toe Syndrome Blue Tongue Sign Blue Tongues in Children Blue Top Tube blue tulp Blue V dye Blue Valve Syndrome Blue Velvet Blue Vials blue vitriol blue wildebeeste blue wing disease blue, methylene blue-black blue-eared pheasant blue-eared pig disease blue-eyed grass blue-gray Blue-gray cattle blue-green algae blue-green algae poisoning blue-point blue-roan bluebag bluebell (South Africa) blueberry Blueberry Muffin Appearance Blueberry Muffin Baby bluebonnet bluebottle bluebush pea bluecomb bluegrass bluenose blues Blues & Reds bluesedge bluestem bluestone Bluetick coonhound bluetongue Blumberg			Blue-Chip Index Blue-Chip Indexes Blue-Chip Indices blue-chip investment blue-chip stock blue-chip stock Blue-Chip Stocks blue-chipper blue-chipper blue-chipper Blue-Chips Blue-Chips blue-collar blue-collar blue-collar Blue-collar job Blue-collar worker Blue-collar worker Blue-collar workers blue-crowned motmots Blue-Dyed Lymph Nodes Blue-eared Pheasant blue-eared pig disease Blue-eye Blue-eye blue-eyed blue-eyed African daisy blue-eyed boy blue-eyed boys Blue-Eyed Devil blue-eyed grass blue-eyed grasses blue-eyed grasses blue-eyed Mary blue-eyed Marys Blue-eyed soul Blue-Eyed White Blue-Eyes Shining Dragon Blue-Eyes Ultimate Dragon Blue-Eyes White Dragon Blue-faced Leicester Blue-faced Leicester Blue-faced Leicester Blue-faced Leicesters Blue-faced Leicesters Blue-faced Leicesters Blue-faced parrot finch blue-flowered blue-fruited Blue-grass State blue-gray blue-gray Blue-gray cattle Blue-gray Gnatcatcher blue-green blue-green alga blue-green alga blue-green alga blue-green algae blue-green algae blue-green algae

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