Eye Dictionary

Eye Dictionary - C

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cable temple: Type of eyeglass temples (side pieces) that wrap around the ear to keep them well-fastened.
calcarine sulcus: The portion of the occipital lobe of the brain where sight takes place. The central visual field is represented in the posterior calcarine sulcus. The peripheral visual field is represented in the anterior portion of the calcarine sulcus.
cancer: eye: Cancer is a disease characterized by abnormal and uncontrollable growth of cells. The resulting mass, or tumor, can invade and destroy surrounding normal tissues. Cancer cells from the tumor can spread starting new cancers in other parts of the body. Melanoma is the most common cancer within the eye. Although rare, congenital or acquired eye cancer is a very debilitating disease. Early diagnosis and treatment is critical.
carbon fiber graphite (CFG): A material made of nylon and carbon that provides the endurance of metal frames but is thin and lightweight. Although the material is black in its natural state, it is now available in a wide range of colors.
carotenoids: Any plant or animal with yellow to red pigments
cataract: Clouding of the natural lens of the eye, usually a process of aging or excessive exposure over the years to ultra violet sun rays, causing blurred vision. Most people over 60 years of age have some degree of cataracts. During modern cataract surgery, this natural lens is removed and replaced by an intraocular lens.
See Cataract in Eye Care Encyclopedia.
See Free Eye Tests.
cauterization: The use of heat to destroy abnormal cells. Also called diathermy or electrodiathermy.
cellulose acetate (zylonite): The most commonly used plastic in eyeglass frames because it is relatively inexpensive, easy to work with, and comes in a wide variety of colors, textures, and patterns. The material is easily adjusted but tends to get brittle with age.
cellulose proprionate: A lightweight material used in eyeglass frames that can be injection molded, making it ideal for intricate designs. Care must be taken when heating and adjusting frames made of this material because it will shrink and ruin with overheating.
chalazion of the eyelid: Inflammatory lump in a meibomian gland of the eyelid. This gland, located just inside the eyelid, supplies the outer portion of the tear film, preventing rapid tear evaporation and overflow and providing airtight eyelid closure.
See Basic Anatomy.
children: eyeglass frames: Eyeglass frames for children come in many attractive, fashionable and durable styles. Metal frames with flexible hinges for durability and nose pads for comfort are recommended. In recent years, eyeglass frame companies have introduced many frame styles that meet these criteria and provide children with selections that are attractive to them – an important consideration in a child’s willingness to wear eyeglasses regularly.
See Free Eye Tests.
children: eyeglasses: Children’s eyeglasses should be fitted by a trained eyecare professional (optician) experienced at working with children. Comfort, safety and durability are top considerations in the selection of eyeglasses for children. Lenses in children’s glasses should be made of impact-resistant polycarbonate that resists breakage and provide greater safety.
See Free Eye Tests.
choroid: Layer of major blood vessels, which lies between the retina and the sclera (white of the eye), that provides oxygen and nutrients to the retina.
See Basic Anatomy.
choroidal hemangioma: A noncancerous growth within the “choroid” blood vessel layer, which lies beneath the retina. Many choroidal hemangiomas never grow or leak fluid, and the ophthalmologist observes them without treatment. However, if the growth is located in the macula (center of vision) or if it leaks fluid, it requires treatment because it can cause a retinal detachment or other vision problem.
choroidal melanoma: Relatively rare malignant melanomas that form in the choroid, the blood vessel layer beneath the retina. Small melanomas can be treated and are usually watched for growth prior to treatment. Medium to large sized melanomas are usually treated with either radiation therapy or removal of the eye.
choroidal metastasis: Sometimes, malignant tumors from other parts of the body can spread to areas in and around the eye. In women, these are usually from the breast, while in men they are more often from the lung. Chemotherapy can sometimes be used to treat these tumors, although radiation is usually a more definitive treatment.
choroidal nevus: Rare tumors that can grow into a malignant melanoma. Like a raised freckle on the skin, nevi can occur inside the eye and should be seen by an eye doctor.
choroidal osteoma: Benign bony tumors that can arise within the choroid blood vessel layer beneath the retina. They are usually located near the optic nerve and can cause vision loss.
closed-angle glaucoma: Serious form of glaucoma that can result in a sudden rise in intraocular pressure. Condition develops when the drainage angle, which allows the aqueous (fluid behind the iris) to flow out of the eye, is suddenly blocked. Symptoms of a partial blockage can include blurred vision, halos around lights, pain and redness of the eye. A sudden blockage can result in severe pain. To avoid permanent damage to the eyes, an ophthalmologist should treat the symptoms immediately.
See Glaucoma in Eye Care Encyclopedia.
See Free Eye Tests.
cobalt: Eyeglass frame material that appears in high-quality frames that are lightweight, durable, flexible, and thin. It can also be coated successfully with a variety of colors, but is very expensive and consequently limited in use.
collagen: In referring to the eye, collagen is the protein fibrils within the corneal tissue that help sustain its shape. Some new refractive vision correction procedures heat these fibrils with a special laser causing them to shrink and change the shape of the cornea.
CO2 laser: High-energy laser that can be used for making surgical incisions and for skin resurfacing. Emits short, intense bursts of energy that vaporize the outer layer of skin without damage to the underlying skin.
color blindness: Color blindness occurs when color-sensitive cone cells in the eye fail to properly pick up or send correct signals to the brain. Red-green deficiency, the most common form, results in the inability to distinguish certain shades of red and green. Those with a less common type have difficulty distinguishing blue and yellow. In rare cases, no colors can be detected, only shades of black, white and gray. Color blindness is usually inherited and cannot be cured, but those affected can often be taught to adapt to the inability to distinguish colors. In some cases, a special red tinted contact lens is used in one eye to aid persons with certain color deficiencies.
See Color Blindness in Eye Care Encyclopedia.
See Free Eye Tests.
color deficiency: Partial or total inability to distinguish specific colors.
See Color Blindness in Eye Care Encyclopedia.
comfort-cable temples: Side pieces of the eyeglass frame that hook behind the ear with a flexible metal cable and are good for children's glasses and for sport safety glasses.
computer eyestrain
computer vision syndrome: Collection of symptoms brought about by eyestrain associated with prolonged use of the computer. Symptoms include eyestrain, blurred vision, headaches, flickering or flashing sensations, loss of appetite, nausea and dry or irritated eyes.
See Free Eye Tests.
See Computer Vision Syndrome in Eye Care Encyclopedia.
computers and your vision: Extensive viewing of the computer screen can lead to eye discomfort including dry, burning eyes, blurred vision, delayed focusing, altered color perception and headaches. Eyestrain is caused by such factors as lighting, location of screen and quality of monitor and/or inherent problems with eyes including refractive disorders, binocular vision, accommodative disorders, dry eye, and poor tear flow over the eye due to reduced blinking.
See General Eye Care in Free Eye Tests.
See Computer Vision Syndrome in Eye Care Encyclopedia.
computer lens: Vision correction lens designed so the monitor and papers next to it are in focus when the head is held in a natural position.
concave: With respect to an eyeglass lens, refers to the surface of the lens that curves inward. A concave surface is always on the back side of a lens.
cone: A type of specialized light-sensitive cell (photoreceptor) in the retina that provides sharp central vision and color vision. Highly concentrated in fovea. Three classes of cones exist: short, medium, and long wavelength cones.
See Basic Anatomy.
conjunctiva: Thin, transparent membrane that lines the inner surface of the eyelid and covers the sclera where it becomes the white of the eye.
See Basic Anatomy.
conjunctival tumor: Malignant cancers that grow on the surface of the eye. The most common conjunctival cancers are squamous carcinoma, malignant melanoma and lymphoma.
conjunctivitis: Inflammation of conjunctiva or membrane that covers the white of the eye and inner surfaces of the eyelid. Characterized by discharge, grittiness, redness and swelling. May result from virus, bacteria, allergens, chemical exposure or ultraviolet light exposure and, depending on cause, can be contagious. Sometimes called pink eye.
See Conjunctiva in Basic Anatomy.
contact lens: Thin plastic or glass lens designed to fit over the surface of the cornea, usually for correction of a refractive error, but can also be cosmetic (colored lenses).
contact lens: aspheric: Premium contact lens for borderline astigmatic patients and emerging presbyopes.
contact lens: bi-toric: Toric contact lens used to correct residual astigmatism.
contact lens: cleaning: All contact lenses, including soft and rigid designs, require cleaning, disinfecting and rinsing solutions. Enzymatic cleaners may also be needed to reduce the buildup of protein deposits on the lens surface. Wearers should follow carefully the cleaning instructions provided by their eye care professional.
contact lens: care: For maximum success with contact lenses, wearers should follow the wear schedule prescribed by their eye professional, practice good hygiene by keeping lenses free from contamination, and use cleaning, disinfecting and rinsing solutions as directed.
contact lens: enzymatic cleaner: Contact lens cleaner that removes protein deposits and other debris. Some come in liquid form while others are in tablet form that is dropped into a solution along with the lens.
contact lens: daily wear: Contact lenses worn only during waking hours.
contact lens: disposable: Contact lenses intended to be worn for a certain time period — daily, weekly, bi-weekly, monthly — and then discarded. Disposable lenses last from one day to two weeks, while “frequent replacement” lenses are thrown away monthly or quarterly.
contact lens: drops: Lubricant eye drops to soothe and moisten lenses to minimize dryness and make lens wear more comfortable. Care should be taken by contact lens wearers to use eye drops specifically formulated for contacts. Other drops may stain lenses.
contact lens evaluation
See Free Eye Tests.
contact lens: extended wear: Contact lenses that can be worn continuously, even while sleeping, up to a maximum number of days, as specified by the eye doctor, usually one to seven days. Extended wear lenses are manufactured from a high water content material and/or a thin center thickness to allow maximum oxygen transmission.
contact lens: frequent replacement: Contact lenses replaced on a planned schedule, usually every 2 weeks, monthly or quarterly. Can be daily or extended wear lenses.
contact lens: hard: Hard contact lenses are manufactured using rigid materials that essentially provide a new front surface for the eye. These lenses help in the correction of astigmatism because the tear film of the eye fills in the gap between the lens and the irregularly shaped cornea.
contact lens: rigid gas permeable (RGP): Durable contact lenses made of polymers that transmit oxygen and allow longer wearing times than other rigid lenses. Because RGPs do not contain water, they resist deposits and are not prone to harboring bacteria. These lenses are large in diameter to increase comfort.
contact lens: soft: Made from flexible plastic, these lenses absorb water and thus enable greater amounts of oxygen to pass through the lens to the cornea. Soft lenses are more comfortable for most wearers than hard lenses, and most lenses prescribed today are a version of a soft lens. They vary in design depending on the type of materials and required refractive correction.
contact lens: solution: Variety of solutions for caring for contact lenses, including cleaning, rinsing and disinfecting. There are also multi-purpose solutions that provide all three functions. Rewetting solutions are designed to lubricate the lenses while they are worn.
contact lens: spheric: Single prescription contact lenses with smooth spherical surfaces that bend light rays equally in all directions (360 degrees).
contact lens: toric: Contact lenses that contain a cylinder component to correct astigmatism by bearing two different optical powers at right angles to each other. These lenses may be thicker in one meridian to enable the lens to maintain proper orientation on the eye.
contact lens and children’s vision: Although children adapt well to contact lenses, they may have problems with proper care. Without adequate supervision, they often wear lenses too long, fail to care for them properly and lose them frequently. Children are also more affected by seasonal allergies and therefore have increased levels of mucoprotein, a naturally occurring substance in tears. This means the contact lenses require more cleaning. Parents should rely the recommendations of an eye care professional because there are cases in which contact lenses are the best choice for a child.
See Pediatric in Free Eye Tests.
contrast sensitivity: Measure of visual ability to distinguish details between an object and its background under varying degrees of contrast.
See Contrast Sensitivity in Eye Care Encyclopedia.
convergence: Coordinated movement of the two eyes so that the images of a single point fall on corresponding points of the two retinas
convex With respect to an eyeglass lens, refers to the surface of the lens that curves outward.
copolyamide (MXP7): A blend of nylon manufactured for eyeglass frame-injection molding. The material is strong, lightweight, and durable, and it retains its shape unless heated.
cornea: Clear structure that covers the front part of the eye including the iris and pupil. The cornea provides most of the eye’s optical power, while the crystalline inner lens, located behind the iris serves to “fine tune” the focus of the images. When both are working properly, a sharp image is focused on the retina and transmitted through the optic nerve to the brain.
See Basic Anatomy.
corneal abrasion: A tearing, scrape or puncture of the cornea, sometimes accompanied by a loss of epithelium, the outer tissue layer of the cornea. Although a corneal abrasion can be very painful, the corneal layer of the eye heals more quickly than most other tissues in the human body.
corneal dystrophy: Any of a number of rare hereditary abnormalities that are characterized by an accumulation of abnormal material in the cornea. This accumulation may occur later in life and result in cloudiness of the cornea and reduction in vision.
corneal implants: Refractive surgery procedure in which a prescription implantable contact lens (ICL) is inserted within the corneal tissue to correct problems of nearsightedness. Two types of lenses are currently being used in the ICL procedure, both under FDA investigational protocol.
corneal mapping: Procedure whereby a detailed map of the corneal surface is drawn by a corneal topography instrument. Maps are used to evaluate the cornea prior to treatment and are especially valuable as a tool in preparing for refractive vision correction.
corneal ring: Plastic half-ring segments used in a particular type of refractive surgery. This procedure involves implantation of the ring segments in the peripheral area of the cornea in order to change its contour to the shape desired to correct cases of nearsightedness. These rings may later be removed or replaced.
corneal topography: Procedure that creates detailed maps of the surface of the eye using an instrument that combines a computer and video camera. The maps are used to evaluate the cornea prior to treatment and are especially valuable as a tool in preparing for refractive vision correction.
corneal ulcers: Wound on the surface of the eye similar to a scrape or cut on the skin. The cornea is covered by a layer of tissue called the epithelium which, when damaged can result in infection if left untreated. Corneal ulcers have many causes including injury, abnormal eyelashes, absence of tear production and infections. Persistent irritation or redness is reason to see an eye doctor.
crossed eyes: Also known as strabismus, this condition is a visual defect in which the eyes are misaligned and point in different directions. Strabismus usually occurs in childhood, but it can occur later in life. Children with crossed eyes usually adapt when the brain learns to ignore the image of the misaligned eye, although they lose depth perception. Adults who develop the problem often have double vision because the brain is already trained to see two images.
See Strabismus in Eye Care Encyclopedia.
See General Eye Care in Free Eye Tests.
crystalline lens: The lens of the eye.
cylindrical surface: With respect to eyeglass lenses, is not evenly curved, but more like an egg or a football.