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 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.
