“C” selections in the Glossary of Terms for
Anatomy, Physiology & Pathology of the Human Eye

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C, vitamin
see vitamin C

canal of Schlemm
Schlemm’s canal; a circular canal lying in the substance of the sclero-corneal junction of the eye and draining the aqueous humor from the anterior chamber into the veins draining the eyeball

canal, Cloquet’s
see Cloquet’s canal

a membrane or saclike structure enclosing a part or organ, such as the membrane around the crystalline lens

cardinal positions of gaze
the six positions in which the eyes can be turned where each eye is controlled primarily by one muscle: up/right, right, down/right, down/left, left, and up/left

cataract, primary
a clouding of the crystalline lens of the eye or its surrounding transparent membrane that hinders or obstructs the passage of light through the lens, resulting in blurry, hazy, or distorted vision

cataract, secondary
a clouding of the posterior capsule of the crystalline lens of the eye, following primary cataract extraction, alleviated by penetration with a YAG laser in a capsulotomy procedure

the burning, searing, or destruction of tissue, using a hot iron or caustic substance, such as to close a tear duct to keep more tears in the eye as a treatment for a dry eye condition

cells, bipolar
see bipolar cells

cells, blood
see blood cells

cells, ganglion
see ganglion cells

cells, goblet
see goblet cells

central retinal artery
a branch of the ophthalmic artery that enters the retina from the middle of the optic nerve and branches to form the arterioles of the retina

central retinal artery occlusion (CRAO)
blockage of the central retinal artery entering the eye through the optic nerve; can result in sudden, severe, and painless loss of vision; often caused by a clot (embolus) originating from the carotid artery; also can be caused by atherosclerotic changes, inflammatory endarteritis, angiospasm, or hydrostatic arterial occlusion; more likely to occur when atherosclerosis (hardening of the arteries) is present; results in the appearance of a “cherry red macula” (aka, “cherry red spot”)

central retinal vein
a vein that is formed by union of the veins draining the retina and which passes into the middle of the optic nerve and empties into the superior ophthalmic vein

central retinal vein occlusion (CRVO)
blockage of the central retinal vein leaving the eye through the optic nerve; can result in retinal hemorrhages, dilated tortuous retinal veins, cotton-wool spots, macular edema, optic disc edema, and vision loss; can be caused by hypertension, diabetes, atherosclerosis, inflammation, thrombus, or glaucoma; may be either ischemic (more severe, which can lead to neovascular glaucoma) or nonischemic (milder, which can resolve on its own)

centralis, fovea
see fovea centralis

central serous chorioretinopathy (CSCR)
painless disorder affecting the central retina (macula or para-macular area), usually only of one eye, where a collection of fluid under the retina causes a gradual blurring of vision, a distortion of objects, and sometimes a transitory increase in hyperopia; affects usually men 20-50, and often is associated with emotional or work-related stress

a small circumscribed tumor of the eyelid formed by retention of Meibomian gland secretions (oil) and sometimes accompanied by inflammation; removed through an incision made in the posterior portion of the affected eyelid

chamber, anterior
see anterior chamber

chamber, posterior
see posterior chamber

chiasm, optic
see optic chiasm

the inner of the two vascular layers of the choroid of the eye that is composed largely of capillaries

inflammation of the choroid and retina of the eye

choroid coat; a vascular membrane containing large branched pigment cells that lies between the retina and the sclera of the eye

an inflammation of the choroid

ciliary body
an annular (ring-like) structure on the inner surface of the anterior wall of the eyeball, contained within the uveal tract and composed largely of the ciliary muscle and bearing the ciliary processes

ciliary muscle
a circular band of smooth muscle fibers situated in the ciliary body and serving as the chief agent in accommodation when it contracts by drawing the ciliary processes centripetally and relaxing the suspensory ligament of the crystalline lens, permitting the lens to become more convex

ciliary processes
vascular folds on the inner surface of the ciliary body that give attachment to the suspensory ligaments (zonules) of the crystalline lens

ciliary spasm
an involuntary contraction of the ciliary muscle

ciliary zonules
see zonules of Zinn

Cloquet’s canal
an anterior-posterior canal through the middle of the vitreous humor in which the hyaloid artery was located prior to birth, the wall of which consists of multi-fenestrated sheaths, previously the basal lamina of the hyaloid artery

closed angle glaucoma
see glaucoma, closed angle

an insoluble fibrous protein of vertebrates that is the chief constituent of the fibrils of connective tissue (as in skin, tendons, and vitreous humor) and of the organic substance of bones and yields gelatin and glue on prolonged heating with water

color blindness
achromatopsia; very rare total color deficiency in which the colors of the spectrum are seen only as shades of white, gray and black

color deficiency
inability to distinguish some colors and shades; occurs when the color-sensitive cone cells in the retina do not properly pick up or send normal color signals to the brain

color vision
ability to distinguish colors and shades; occurs when the color-sensitive cone cells in the retina properly pick up and send normal color signals to the brain

color, eye
the visible color of the iris of the eye, determined genetically

compartment, anterior
see anterior compartment

compartment, posterior
see posterior compartment

hollowed, arched, curved, or rounded inward like the inside of a bowl or the back surface of a spectacle or contact lens

the conical light-sensitive receptor cells of the retina that function in color vision and in the perception of fine detail; composed of an outer segment (containing the photoreceptor molecule iodopsin, which is composed of photopsin and retinene), inner segment, cell body, and synaptic region; about 6½ to 7 million per eye, much fewer than the number of rods; densest accumulation is in the macula and, especially, the fovea; absent in the optic disc (optic nerve head)

the mucous membrane that lines the inner surface of the eyelids and the sclera on the front of the eyeball

conjunctiva, bulbar
the clear mucous membrane that covers the sclera on the front of the eyeball

conjunctiva, palpebral
the mucous membrane that lines the inner surface of the eyelids

“pink eye”; infection and inflammation of the conjunctiva, usually from an allergy, a virus, or a bacterium

constriction, pupil
see pupil constriction

contact lens
a thin rigid or soft lens designed to fit on the front surface of the cornea and usually worn to correct defects in vision

convergence excess
over-convergence of the eyes at a near distance, such as when reading, writing, drawing, or viewing a computer screen; can result in headaches, dizziness, and nausea/or, which can lead to an inability to concentrate and even irritability; can result when the medial rectus muscles are stronger than the lateral rectus muscles; often can be treated with plus lenses, visual therapy, and/or base-out prismatic power in lenses

convergence insufficiency
difficulty or inability of the eyes to converge and work together at a near distance for extended periods of time, such as when reading, writing, drawing, or viewing a computer screen; can result in headaches, dizziness, and/or nausea, which can lead to an inability to concentrate and even irritability; can result when the lateral rectus muscles are stronger than the medial rectus muscles; often can be treated with visual therapy and/or base-in prismatic power in lenses

arched, curved, or rounded outward like the exterior of a sphere or circle or the front surface of a spectacle or contact lens

the transparent, anterior, dome-shaped portion of the eyeball that covers the iris and pupil, acting like a window which admits light into the eye

corneal ring implantation
surgical procedure in which a tiny plastic ring is inserted into the cornea, thus reshaping the cornea to refocus entering light to correct for myopia (nearsightedness), hyperopia (farsightedness), or astigmatism

corneal transplantation
the transference of healthy corneal tissue from one individual to the eye of another individual after a portion the latter’s diseased cornea has been removed surgically

the outer or superficial part of an organ or body structure, such as the layer of the crystalline lens peripheral to the nucleus or the outer layer of gray matter of the cerebrum and cerebellum

cortex, lenticular
see lenticular cortex

cortex, visual
see visual cortex

any of various adrenal-cortex steroids (as corticosterone, cortisone, and aldosterone) used medically, especially as anti-inflammatory agents

cotton wool spots
small white areas in the retina caused by ischemic infarction of the nerve fiber layer of the superficial retina and due to occlusion of precapillary arterioles; do not threaten vision but can be indicative of a serious medical condition, such as diabetes, hypertension, cytomegalovirus infection, or HIV infection (AIDS)

cranial nerve
any of the 12 paired nerves that arise from the lower surface of the brain with one of each pair on each side passing through openings in the skull to the periphery of the body; olfactory (I), optic (II), oculomotor (III), trochlear (IV), trigeminal (V)—including ophthalmic (V1), maxillary (V2), and mandibular (V3)—abducens (VI), facial (VII), vestibulocochlear (VIII), glossopharyngeal (IX), and vagus (X)

cribrosa, lamina
see lamina cribrosa

crossed eye
see esotropia

see intracapsular cataract extraction (ICCE)

the therapeutic use of cold to treat human tissue, as in a retinal tear to seal the retina to the wall of the eye again in an attempt to prevent further detachment

crystalline lens
the highly transparent biconvex, lens-shaped or nearly spherical body in the eye, situated immediately behind the pupil, which focuses light rays entering the eye typically onto the retina

inflammation of the ciliary body

cystoid macular edema (CME)
see edema, cystoid macular (CME)

cytomegalovirus (CMV)
any of several herpes viruses (Herpesviridae) whose infection causes cellular enlargement and formation of eosinophilic inclusion bodies, especially in a cell’s nucleus; transmitted by sexual contact or exposure to infected body fluids; not highly contagious and occasionally produces mononucleosis-like symptoms in otherwise healthy adults, but acts as an opportunistic infectious agent in immunosuppressive conditions (such as AIDS)

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