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Eye Health Glossary

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canal of schlemm

A tiny tubular canal that is responsible for transporting aqueous humour from the trabecular meshwork to the bloodstream. It can be found at the limbus, which is where the cornea and the iris come together.

canaliculitis

Canaliculitis is a relatively rare eye condition in which the canal that ends at the punctum (which is the tiny hole at the tip of the upper and lower eyelids) becomes infected. Resulting symptoms include a red and watery eye, as well as a red and puffy eyelid, which may or may not release discharge through the punctum. Treatment depends on the severity of the discharge and response to antibiotics.

cataract

Opacification (clouding) of the natural crystalline lens of the eye, which is responsible for focusing light to produce clear images. There are three types of cataract: cortical cataract, nuclear cataract, and subcapsular cataract. Learn more about cataracts & cataract surgery.

cellulitis

Cellulitis literally means “inflammation of the cells” which in itself is horribly ambiguous. Most often, however, cellulitis refers to an acute spread of infection among skin cells, leading to pain, redness, swelling, and warmth in the area affected. Learn more about Cellulitis.

central vision

Central vision is arguably the most important part of a person\s vision. It is generally accepted that central vision involves the central 30 degrees of vision, with all visual space outside of that being speripheral vision. In macular degeneration (and all other eye disorders affecting the macula), central vision is affected.

chalazion

Non-infectious nodule on the upper or lower eyelid that does not produce pain when palpated (pushed on). Learn more about Chalazion.

chemosis

Swelling of the clear thin membrane (conjunctiva) that covers the white part of the eye (sclera). When swollen, the conjunctiva becomes fluid-filled and essentially puffs outwards from the eye. It is not uncommon for swelling to become so severe that the eyelids cannot close properly. Treatment consists of determining and treating the underlying cause of chemosis.

choroid

The choroid lies between the retina and the sclera within the eye. It contains a network of blood vessels that are responsible for nourishing the back of the eye.

cicatricial

Pertaining to (or of the nature of) a scar. Cicatricial conditions are so named because they often result in scarring.

ciliary body

The ciliary body is a structure within the eye located behind the iris. The ciliary body is responsible for producing aqueous humour. The ciliary body also takes on an important role in accommodation by changing the shape of the crystalline lens. Occasionally, eyecare professionals will use cycloplegic agents to paralyze the ciliary body which prevents accommodation from occurring.

cold compresses

A cold compress is any material that can be cooled (but not so cold that it hurts – if you use ice, then wrap a towel around it before applying it to the eye) and then placed against the eye with gentle pressure. They are particularly useful following a scratch to the eye or perhaps to reduce the swelling of an imminent black eye following a fist fight. The cold temperature helps to constrict blood vessels, which reduces redness and swelling.

coloboma

A coloboma is a cleft or gap in an eye structure. It can occur at any structure (most notable is an iris coloboma, but it can also occur in the eyelid, lens, choroid, or optic disc) and the location where it occurs is related to the point in fetal development at which growth was halted. The human eye develops during the first trimester of pregnancy after which the optic fissure must close in order to complete eye development. In cases of coloboma, the optic fissure has not properly closed.

color blindness

Color blindness is not so much the inability to see color (which is extremely rare in humans) but the inability to see as many shades of color as a person with normal color vision. The incidence of color blindness (or color vision deficiency) is much higher in males than in females because it is inherited via the X-chromosome. Learn more about Color Blindness.

cone

Cones are photoreceptors that are so named because they are shaped like cones. They are found almost exclusively in the region of the fovea within the retina and are responsible for producing crisp, color vision.

conjunctiva

A thin, transparent film that covers the white part of the eye (sclera) as well as the surface of the inner part of the eyelids.

convergence

Inward movement of both eyes towards the nose. Proper convergence is necessary when shifting views from a distant target to a near target in order to maintain clear, single binocular vision.

convergence excess

A binocular vision problem mostly occurring in young children, in which the eyes converge too much when attempting to look at a near object (such as a book). If this occurs as a result of excessive accommodation, the problem may be remedied with the use of bifocal lenses.

convergence insufficiency

A binocular vision problem most commonly occurring in young adults, in which the eyes do not properly converge. Symptoms of convergence insufficiency include headache, eyestrain, blurred vision, and fatigue when viewing close objects or reading. Once diagnosed, convergence insufficiency can potentially be treated with eye exercises (orthoptics), which can strengthen the muscles responsible for turning the eyes inwards.

cornea

The clear tissue that forms a dome above the iris. The cornea is responsible for 2/3 of the focusing power of the eye: because of this, it is the site of many refractive procedures and devices, such as LASIK, PRK, and contact lenses.

corneal curvature

A measure of the curvature of the surface of the cornea. This measurement is useful to optometrists and ophthalmologists for contact lens fittings as well as for monitoring eye conditions such as keratoconus.

cortical cataract

One of three types of cataracts; cortical cataracts most often initially affect the peripheral parts of the crystalline lens so they usually have little impact on vision, although the spoke-like opacities may result in mild to severe glare. Learn more about Cataracts.

crossed eyes

Crossed eyes that face inwards are most noticeable upon looking at a person; this type of crossed eyes is known as esotropia. When one of the eyes is facing outwards, this is known as exotropia. All types of crossed eyes are known as strabismus.

crystalline lens

The natural lens of the eye, responsible for accommodation, as well as 1/3 of the focusing power of the eye. With age, the lens continues to grow in size, forming layers similar to that of an onion. The oldest part of a lens is the middle of it, and since new layers of cells are forming around old layers, there is no room for dead cells to be sloughed away, which is believed to be part of the reason why the lens becomes cloudy with age, forming a cataract.

cup

A popular medical term for the optic cup. The optic cup lends gets its name from the slight cupping of the optic nerve at the point where it meets the retina. Damage to the optic nerve fibres is an integral aspect in the pathophysiology of glaucoma. Learn more about cupping in glaucoma.

custom LASIK

Custom LASIK is a relatively new procedure that takes advance of wavefront technology to eliminate both higher order and lower order aberrations in the eye during laser eye surgery. Learn more about Custom LASIK surgery.

cyclopia

Exceedingly rare birth defect in which only one eye develops. The eye is centrally located in the face, above which a proboscis may or may not exist instead of a nose.

cycloplegia

A condition in which the ciliary body muscles are unable to contract and accommodation is prevented. Occasionally, eye care professionals will use cycloplegic agents to paralyze the ciliary body which prevents accommodation from occurring. This is especially useful when doctors are determining the prescription of a young child who tends to accommodate too much.

cyclotropia

A type of strabismus in which the eye is permanently rotated within its orbit either clockwise or counterclockwise.

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