Home Resources » Glossary: C-D

Glossary of Eye Care Terms - C-D



cable temple A type of "arm" of a pair of glasses that wraps around the ear, to keep the eyewear firmly attached. Often used in eyeglasses for infants and toddlers.

canaliculus Tiny, tube-shaped passageway in the body. In the eye, canaliculi are tiny channels at the beginning of tear ducts through which tears drain until they exit into the nose.


capsulotomy In cataract surgery, an incision into the capsule that contains the natural crystalline lens of the eye, in order to remove and replace the natural lens with an artificial one.








cerebral palsy Group of chronic conditions caused by brain damage before birth or during infancy. The many effects may include poor muscle coordination/control, muscle weakness/tightness, involuntary movements, difficulty with swallowing, speech problems, seizures, sensory impairment, learning disabilities and mental retardation. No cure exists, but training and therapy can improve function and quality of life.


chemosis Conjunctival swelling that is often caused by an allergy.

choroid Layers of blood vessels located between the sclera (white of the eye) and the retina; they provide nourishment to the back area of the eye. Read more about the choroid.


chromosomes Paired strands of DNA that contain genes or inherited traits. Each normal cell in the human body typically has 23 pairs of chromosomes, 46 altogether, with one half contributed by the mother and the other half contributed by the father.








color blindness Partial or total inability to distinguish specific colors. Color blindness is inherited and is much more common in men than in women. Read more about color blindness.

computer vision syndrome Collection of problems, mostly eye- and vision-related, associated with computer use. Symptoms include eye strain, dry eyes, blurred vision, red or pink eyes, burning, light sensitivity, headaches and pain in the shoulders, neck and back. Please read our articles on computer vision syndrome to learn more.

cone A photosensitive receptor in the retina that helps you to see color. Learn more about the retina.

conjunctiva The thin, normally clear, moist membrane that covers the "white" of the eye (sclera) and the inner surface of the eyelids. Learn more about the conjunctiva of the eye.

conjunctivitis Inflammation of the conjunctiva, characterized by a pink eye. The cause is either infectious or allergic, though the term "pink eye" is commonly used for any type of conjunctivitis. Other symptoms include burning, discharge, dryness, itching, light sensitivity, eye pain or discomfort, stickiness, tearing and chemosis.

contact lens drops Eye drops for contact lens wearers; regular eye drops can discolor contact lenses.

contact lens problem Contact lens problems can range from minor to sight-threatening, and include protein build-up, debris on the lens, a ripped or nicked lens, infections and more. Symptoms can include frequent blinking, blurred vision, burning, discharge, foreign body sensation, itching, light sensitivity, eye pain or discomfort, a red or pink eye or lid and eyelid swelling. For tips on what to do about contact lens discomfort, please read our article.

contrast sensitivity The ability of the eye to detect the line of demarcation between an object and its background or an adjacent object. Learn more about contrast sensitivity.

convergence Eyes' ability to turn inward. People with convergence insufficiency have trouble (eye strain, blurred vision, etc.) with near tasks such as reading.

cornea The clear portion of the front surface of the eye that allows light to enter the eye for sight. The cornea provides most of the focusing power of the eye. Learn more about the cornea of the eye.



corneal collagen crosslinking A medical procedure that involves the application of riboflavin (vitamin B2) eye drops and ultraviolet light to the eye to strengthen corneal tissue in an eye affected by keratoconus. Learn more about corneal collagen crosslinking.

corneal dystrophy One of a group of conditions, usually hereditary, in which the cornea loses its transparency. The corneal surface is no longer smooth. Common forms include map-dot-fingerprint dystrophy, Fuchs' dystrophy and lattice dystrophy. Symptoms include blurred vision, foreign body sensation, light sensitivity, eye pain or discomfort and vision loss.

corneal ecstasia A progressive thinning of the middle layer of the cornea (stroma) causing the front surface of the eye to bulge forward. Ectasia causes irregular astigmatism, higher-order aberrations, distorted vision and corneal scarring. Causes of corneal ectasia include keratoconus, other corneal diseases, and (infrequently) LASIK surgery. Also called keratectasia or keratoectasia.



corneal implants Devices (such as rings or contacts) placed in the eye, usually to correct vision. Read more about corneal inserts.


corneal refractive therapy (CRT) The use of specially designed gas permeable contact lenses to reshape the cornea during sleep and temporarily correct myopia (with or without mild-to-moderate astigmatism). Developed by Paragon Vision Sciences. Similar to orthokeratology.






crossed eyes Type of strabismus (a misalignment of the eyes) where one or both eyes point inward, toward the nose.Learn more about crossed eyes.

culture In medical terminology, tests of samples such as blood or body material to determine possible presence of bacteria or other substances.

cycloplegia Paralysis of the eye's ciliary (focusing) muscle and power of accommodation. A cycloplegic refraction is one that is performed after eye drops are placed in the eye to dilate the pupil and temporarily paralyze the accommodative ability of the eye that might mask some degree of refractive error.








Descemet's membrane Corneal layer between the stroma and the endothelium.

diabetic maculopathy Eye disease related to diabetes that creates swelling and abnormal leakage of fluids and fats into the


diabetic retinopathy Leaking of retinal blood vessels in advanced or long-term diabetes, affecting the macula or retina. Most people have no symptoms at first, but can develop blurred near vision, double vision, floaters, retinal/vitreous hemorrhages and metamorphopsia. In later stages, you can also suffer vision loss. For more information about diabetes and related eye disease, please read our article on diabetic retinopathy.

diabetic vitreous hemorrhage Bleeding into the gel-like (

) interior of the eye, originating from blood vessels weakened by diabetes. Because blood in the vitreous can block vision, a vitrectomy may be required.

diode A device, such as a semiconductor, that conducts electricity in one direction. A light-emitting diode (LED) can produce various wavelengths, colors and intensities of light.

diopter Unit of measure for the refractive (light-bending) power of a lens; eye care practitioners use it in both eyeglass prescriptions and contact lens prescriptions. A negative number refers to nearsightedness; a positive number, farsightedness. For example, someone with -8.00 diopter lenses is very nearsighted, while someone with +0.75 diopter lenses is only slightly farsighted.

diplopia Also called double vision (see below).


disposable contact lenses Technically, this is any contact lens that is thrown away after a short period of time. Among most eye care practitioners, "disposable" usage ranges from one day to two weeks, while "frequent replacement" lenses are discarded monthly or quarterly.

distance vision Generally refers to eyesight for tasks beyond arm's length, such as driving, watching television and movies, participating in sports, etc. Distance vision is tested during an eye exam with a standard eye chart at a distance of approximately 20 feet. See also: near vision and intermediate vision.





drugs Many drugs, both legal and illegal, can affect your eyes and vision. These include eye drops, other topical eye medications, pills and more. Symptoms can include blurred vision, burning, dry eyes, eyelash loss, floaters, halos around lights, light sensitivity, pupils that are dilated, small or unresponsive to light, peripheral or general vision loss and jaundice.

druse A small, yellow or white deposit in the eye. "Drusen" is the plural form of the word. Drusen are sometimes signs of macular degeneration.



dry skin Skin that is generally dry may include dry eyelids.


Page updated June 2017