Contact Lens Glossary

If you are new to the world of contact lenses, then our informative contact lens glossary will give you some quick answers to common terms. It is recommended that you visit a qualified eye doctor before ordering contact lenses online.

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Bowman's membrane Corneal layer between the epithelium and the stroma.

bridge The part of eyeglasses that extends across the nose.

cable temple Style of eyeglasses that wraps around the ear, to keep them well-fastened.

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cataract Clouding of the natural lens of the eye, resulting in impaired vision. Cataract surgery involves removing the eye's natural lens, and replacing it with an artificial one.

central island Refractive surgery complication in which the laser leaves an "island" of corneal tissue in the concave ablation zone. Symptoms include double vision and distortion.

choroid Layer of blood vessels and pigments (usually brown or blue) that lies beneath the sclera (the white of the eye). Often mistakenly called the iris.

CK (Conductive Keratoplasty) Procedure wherein a surgeon uses radio waves to heat collagen in the cornea's periphery to shrink it and reduce hyperopia.

ciliary body Part of the eye between the iris and the choroid; the three form the uvea. The ciliary body's main functions are accommodation, aqueous humor production and holding the lens in place.

clip-on Type of glasses that attaches to your regular glasses, such as clip-on sunglasses.

CMV retinitis (cytomegalovirus retinitis) Serious eye infection usually found in those with immune problems, such as AIDS patients; symptoms include floaters, blind spots, blurry vision and vision loss.

collagen Fibrous protein in bones and connective tissue, it is also present in the eye. One type of vision correction surgery heats collagen around the edges of the cornea (which lets light into the eye). This procedure reshapes the cornea, helping it focus light right onto the retina, for clearer vision.

color blindness Partial or total inability to distinguish specific colors.

computer vision syndrome Condition caused by prolonged computer use, and characterized by eyestrain, blurred vision, headaches and dry or irritated eyes.

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

conjunctiva Mucous membrane that lines the visible part of the eye and the inner surface of the eyelid.

conjunctivitis Inflammation of the conjunctiva.

contact lens drops Eyedrops for contact lens wearers; regular eyedrops can discolor contact lenses.

contrast sensitivity The least amount of contrast that you can still see.

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

cornea The clear part of the eye covering the iris and pupil; it lets light into the eye, permitting sight.

corneal abrasion Tearing or puncture of the cornea. Usually causes pain, tearing, light sensitivity, and a feeling that something is in the eye.

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

corneal ring Type of vision correction surgery where a doctor inserts a tiny plastic ring into the cornea (which lets light into the eye). This ring reshapes the cornea, helping it to focus light better onto the retina so you can see better. The ring can be adjusted and even removed if desired.

corneal topography Process of using a camera/computer system to map the cornea for refractive surgery, contact lens fitting and corneal disease management.

corneal ulcer Wound in the surface of the eye caused by injury, dryness due to lack of tear production, or infection.

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

cystoid macular edema (CME) Swelling of the eye's macula, caused by an excessive amount of fluid.

dacryostenosis Blocked tear duct, which is characterized by a lot of tearing.

daily wear These soft contact lenses are worn every day for six months up to a couple of years. They require daily cleaning and disinfecting, as well as a periodic enzymatic soak (usually once a week).

decentered ablation Also called decentration. Refractive surgery complication in which the laser is not centered on the pupil when it removes tissue. Symptoms include glare, double vision and halos.

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

diabetic retinopathy Leaking of retinal blood vessels in advanced or long-term diabetes, affecting the macula or retina. Vision can be seriously distorted or blurred.

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

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

drooping eyelids Also called ptosis. Condition in which the upper eyelid(s) only sag. It can be present at birth or caused by a later problem with the muscles lifting the eyelid, called levators.

druse Small yellow or white deposit in the eye. Drusen are sometimes signs of macular degeneration.

dry eye Lack of sufficient lubrication and moisture in the eye. Most dry eye complaints are temporary and easily relieved; dry eye syndrome is chronic and needs more advanced treatment by an eyecare practitioner.

endothelium The cornea's inner layer of cells.

enzymatic cleaner A cleaner that removes protein deposits and other debris from contact lenses. It's recommended for use either daily, weekly, or monthly. Some enzymatic cleaners are a small tablet dropped into a solution along with the lens; others come in liquid form.

epithelium The cornea's outer layer of cells.

extended wear Currently, these contact lenses are FDA-approved to be worn without removal for up to seven days (or 30 days in the case of two brands), meaning some people will be comfortable sleeping with them in their eyes. Thirty-day contact lenses are sometimes referred to as "continuous wear."

eyecare practitioner Optometrists (O.D.s) and ophthalmologists (M.D.s) both practice eyecare, but in different ways: O.D.s (Doctors of Optometry) examine eyes for both vision and health problems, prescribe glasses, prescribe and fit contact lenses, and treat some eye conditions and diseases. M.D.s are medical doctors who examine eyes, prescribe glasses and contacts, treat disease and perform surgery. Other non-doctor eyecare practitioners include paraoptometrics, contact lens technicians and opticians.

farsightedness Also called hyperopia. To farsighted people, near objects are blurry, but far objects are in focus.

FDA (Food & Drug Administration) A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the U.S., these products must be approved by the FDA before they can be marketed.

flap and zap Slang for LASIK.

floaters Small specks that pass across your field of vision, these are clumps of cells inside the transparent gel filling the eyeball in front of the retina.

fovea A depression in the retina that contains only cones (not rods), and that provides acute eyesight.

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

glaucoma Disease characterized by excessive fluid (aqueous humor) in the eye, high intraocular pressure and vision impairment. Blindness can result.

Graves' ophthalmopathy Thyroid-related, autoimmune eye disorder usually associated with Graves' disease; symptoms include eyelid retraction, bulging eyes, light sensitivity, discomfort, double vision and vision loss.

hard contact lenses Rarely worn now, these are the small, hard lenses made of PMMA material that many people wore in the '70s and '80s. Compared with modern soft and rigid lenses, they are less healthy to wear long-term, since the material doesn't allow oxygen to reach the surface of the eye.

high index Type of lens with a higher index of refraction, meaning that light travels faster through the lens to reach the eye than with traditional glass or plastic. It is denser, so the same amount of visual correction occurs with less material (whether glass or plastic) — so the lens can be thinner.

hyperopia Also called farsightedness. To people with hyperopia, near objects are blurry, but far objects are in focus.

intraocular lens (IOL) Artificial lens that a cataract surgeon places in a patient's eye after removing the eye's natural lens. Like a contact lens, it has a built-in refractive power tailored specifically to the patient's visual condition.

intraocular pressure (IOP) Eye pressure, as determined by the amount of aqueous humor filling it. High IOP (ocular hypertension) can be a sign of glaucoma.

iris Diaphragm that controls the size of the pupil (an opening that lets light in). Many people believe the iris is the colored part of the eye. Actually, that is the choroid, a pigmented layer beneath the sclera (white of the eye).

iritis Inflammation of the iris.

keratectomy Surgical removal of part of the cornea.

keratitis Inflammation of the cornea.

keratoconus Condition in which the cornea develops a cone-shaped bulge that can result in major blurring and distortion.

keratoplasty Any of several types of corneal surgery, such as shrinking the collagen to reduce farsightedness or transplanting a new cornea to treat keratoconus.

keratotomy Incision of the cornea.

lacrimal plug Device to block the lacrimal punctum (an opening at the end of a tear duct), to keep the eye moist.

laser photocoagulation Procedure in which a surgeon uses a laser to coagulate tissue, usually to seal leaking blood vessels and destroy new ones in diseases like macular degeneration and diabetic retinopathy.

LASEK (Laser Epithelial Keratomileusis) Procedure that is similar to LASIK, except that the surgeon cuts a flap in the epithelium only, instead of through the epithelium and part of the stroma. LASEK is used mostly for people with thin or flat corneas who are poor candidates for LASIK, which requires more corneal tissue for success.

LASIK (Laser-Assisted In Situ Keratomileusis) Surgical procedure in which a tiny flap is cut in the top of the cornea, underlying corneal tissue is removed with an excimer laser, and the flap is put back in place. LASIK corrects myopia and hyperopia.

lateral rectus muscle Muscle that moves the eye away from the nose.

lens The nearly spherical body in the eye that focuses light rays onto the retina.

limbus Boundary area connecting the cornea and sclera; the three form the eye's outermost layer.

lipid A fatlike substance that can collect on contact lenses, making them uncomfortable.

low vision Also called partial sight. Sight that cannot be satisfactorily corrected with glasses, contacts, or surgery. Low vision usually results from an eye disease such as glaucoma or macular degeneration.

LTK (Laser Thermal Keratoplasty) Also called Laser Thermokeratoplasty. Surgery to correct mild farsightedness in people over 40; the doctor uses a holmium laser to heat the cornea and shrink its collagen.

lutein An antioxidant that is found throughout the body, but is concentrated in the macula. Lutein is believed to help protect the eyes from free radical damage caused by the sun's harmful rays.

macula Part of the eye near the middle of the retina; the macula allows us to see objects with great detail.

maculopathy Disease of the macula, such as age-related macular degeneration.

medial rectus muscle Muscle that moves the eye toward the nose.

microcornea Abnormally small cornea.

microkeratome Small instrument that surgeons use to cut the cornea.

migraine (ocular) Visual phenomena that may accompany a migraine headache or that may occur without any headache. They include light flashes, spots, wavy lines, flickers, zig-zagging lights, semi-circular or crescent-shaped visual defects and distortions of shapes.

monovision Vision correction method for those with presbyopia in which one eye is corrected for near vision and the other for far, either through contact lenses or refractive surgery. Monovision eliminates the need for reading glasses, but does have some drawbacks, including decreased depth perception.

multifocal Type of spectacle or contact lens design that includes more than one focal area, such as bifocals or trifocals.

myasthenia gravis Autoimmune disease sometimes related to thyroid conditions. Signs are droopy eyelids or double vision that worsen toward the end of the day.

myopia Also called nearsightedness. Condition in which visual images come to a focus in front of the retina, resulting in defective vision of distant objects.

nearsightedness Also called myopia. Condition in which visual images come to a focus in front of the retina, resulting in defective vision of distant objects.

neovascularization Abnormal growth of new blood vessels, such as in an excessive amount, or in tissue that normally does not contain them.

nevus Also spelled naevus. Brown pigmentation resembling freckle or mole on white of the eye. More often found in dark-skinned people. Sometimes malignant.

nickel Metallic element used mainly in alloys. Many eyeglass frames are made of nickel alloy, so people who are allergic should choose a hypoallergenic substitute, such as titanium.

nose pad One of a pair of pads, usually clear, that rest on either side of your nose and help to support your glasses.

nystagmus Condition in which the eye oscillates repeatedly.

OD (oculus dexter) Right eye. Or, doctor of optometry.

ocular hypertension Condition in which the intraocular pressure of the eye is elevated above normal and which may lead to glaucoma.

ocular migraine Visual phenomena that may accompany a migraine headache or that may occur without any headache. They include light flashes, spots, wavy lines, flickers, zig-zagging lights, semi-circular or crescent-shaped visual defects and distortions of shapes.

ophthalmologist A medical doctor (M.D.) who specializes in the eye. Ophthalmologists perform eye exams, treat disease, prescribe medication, and perform surgery. They may also write prescriptions for eyeglasses and contact lenses.

optician Opticians are not doctors, but in some states they must complete training and be licensed. And in some states they can become certified, after special training, to fit contact lenses. Most opticians sell and fit eyeglasses, sunglasses, and specialty eyewear that are made to an optometrist's or ophthalmologist's prescription. Many also have equipment on the premises so they can grind lenses and put them in frames without ordering from a lab.

optic nerve Part of the eye that carries stimuli from the rods and cones to the brain.

optic nerve head Also called optic disk. Circular area where the optic nerve enters the retina, and the location of the eye's blind spot.

optometrist Doctors of optometry (O.D.s) examine eyes for both vision and health problems, prescribe glasses, and fit contact lenses. They can prescribe many ophthalmic medications and may participate in your pre- and postoperative care if you have eye surgery. O.D.s must complete four years of post-graduate optometry school for their doctorate.

orthokeratology (ortho-k) Procedure in which a doctor fits you with special gas permeable contact lenses to reshape your cornea and correct errors like nearsightedness. Often, patients wear the lenses just at night.

OS (oculus sinister) Left eye.

OU (oculus uterque, oculus unitas or oculus uniter) Both eyes.

overconvergence Condition in which the eyes come too far inward when focusing on a near object, resulting in blurring.

papilla Small bump where the optic nerve exits the eye.

pars plana Posterior part of the eye's ciliary body.

peripheral vision The edges of your visual field.

photoablation Procedure in which a surgeon uses ultraviolet radiation to remove tissue.

photochromic Able to change lens color or darkness/density depending upon the degree of exposure to light.

photokeratitis "Sunburn" of the cornea; symptoms include discomfort, blurred vision, and light sensitivity. The temporary vision loss that can result is called "snow blindness."

pingueculum Yellowish, thickened lesion on the conjunctiva. May be caused by irritation from sun, dust and wind.

plano A term eyecare professionals use to describe lenses with no corrective power. The term is most often applied to nonprescription sunglasses or contact lenses that are worn for cosmetic purposes only.

PMMA (polymethyl methacrylate) Old-fashioned hard contacts were made of PMMA, which is not permeable; today's rigid lenses contain other polymers that allow oxygen to reach your eye.

polarized lenses Lenses that block light reflected from horizontal surfaces such as water, to reduce glare.

polycarbonate Plastic that is very impact-resistant, and is thus sometimes used for spectacle lenses and frames.

posterior chamber Part of the eye behind the iris and in front of the lens.

presbyope Person who has difficulty reading print and seeing near objects.

presbyopia Inability of the eye lens to focus incoming light, resulting in blurred vision at a reading distance and eyestrain. Most people develop presbyopia in their 40s.

prescription lenses Lenses that provide vision correction as prescribed by an eyecare practitioner.

PRK (Photorefractive Keratectomy) Surgical procedure in which an excimer laser is used to remove corneal tissue to correct vision problems.

progressive lenses (also, progressive addition lenses or PALs) Multifocal lenses whose corrective powers change progressively throughout the lens. A wearer looks through one portion of the lens for distance vision, another for intermediate vision, and a third portion for reading or close work. Each area is blended invisibly into the next, without the lines that traditional bifocals or trifocals have.

propionate A soft, flexible material that is sometimes used in goggles.

protective eyewear Eyewear made with impact-resistant lenses, usually polycarbonate, that protects the eyes, especially in working situations or sports.

protein An organic substance that can collect on contact lenses, resulting in discomfort and cloudy vision.

pterygium Triangular-shaped fold of tissue on white of the eye. May eventually grow over part of the cornea. May be caused by irritation from sun, dust and wind.

pupil The round, dark center of the eye, which opens and closes to regulate the amount of light the retina receives.

reading glasses (readers) Glasses to help with close work, particularly for people who are presbyopic.

refractive surgery Surgery that corrects visual acuity, with the objective of reducing or eliminating the need for glasses and contacts. Includes radial keratotomy, PRK, LASIK, and corneal implants.

replacement schedule How often you discard and replace your contact lenses: every day, week or two weeks (disposable); or every month, two months or calendar quarter (frequent replacement). It's important to differentiate between replacement schedule and wear schedule. Wear schedule is either daily wear (removed before sleeping) or extended wear (you may sleep with them in).

retina The sensory membrane that lines the eye; it is composed of several layers and functions as the immediate instrument of vision by receiving images formed by the lens and converting them into signals which reach the brain by way of the optic nerve.

retinal detachment Condition where the retina separates from the choroid.

retinitis pigmentosa Condition characterized by the progressive loss of peripheral vision, usually beginning with night blindness.

RGP (Rigid Gas Permeable) Type of contact lens made of breathable plastic that is custom-fit to the shape of the cornea. RGPs are the successor to old-fashioned hard lenses, which are now virtually obsolete.

rod A photosensitive receptor in the retina that helps you to see in low light.

RK (Radial Keratotomy) Surgical procedure where cuts are made in the cornea in a radial pattern, to flatten the cornea and correct myopia.

sclera The outer coat of the eyeball that forms the visible white of the eye and surrounds the optic nerve at the back of the eyeball.

segment A part, as in the near-vision portion of a pair of bifocals.

silicone Type of flexible and comfortable plastic. Because it is commonly used in nose pads in eyeglasses, people who are allergic to silicone should ask their eye doctor for a different type of nose pad.

soft contact lenses Contacts made of gel-like plastic containing varying amounts of water.

solution Product used to clean, disinfect and store contact lenses.

SPF (sun protection factor) Number representing the amount of sun something blocks. For example, if you normally begin to burn after half an hour in the sun, a sunscreen with an SPF of 2 should let you stay out twice as long (1 hour), SPF 4 should let you stay out four times as long, and so on.

spherical A contact lens design that is like a sphere and is fairly common; in contrast, toric lenses for astigmatism are football-shaped and are less common.

spots Small, cloudy specks in the eye that become noticeable when they fall in the line of sight.

spring hinge Type of hinge on eyeglass frames that is more flexible than a regular hinge, making the frames more durable.

strabismus A misalignment of the eyes: they don't point at the same object together. Crossed eyes are one type of strabismus.

stroma The cornea's middle layer; it consists of lamellae (collagen) and cells, and makes up most of the cornea.

sty A blocked gland at the edge of the lid which has become infected by bacteria.

suspensory ligament Also called zonule of Zinn. Membrane of fibers (zonules) that holds the eye's lens in place.

temple The "arm" of a pair of glasses, running from the ear to the lens area.

titanium A type of metal alloy that is very strong. Eyeglasses made of titanium are lightweight, durable and often hypoallergenic.

toric A lens design with two different optical powers at right angles to each other for the correction of astigmatism.

trifocal A lens design that has three focal areas: a lens for close work or reading, a lens for mid-distance viewing or arm's length, and a lens for faraway viewing or driving.

ultraviolet (UV) The invisible part of the light spectrum whose rays have wavelengths shorter than the violet end of the visible spectrum and longer than X rays. UVA and UVB light are harmful to your eyes and skin.

uvea Middle layer of the eye, below the limbus, and consisting of the iris, ciliary body and choroid.

uveitis Inflammation of the uvea.

vitreous body Part of the eye between the lens and the retina, containing a clear jelly called the vitreous humor.

wear schedule How long you wear your contact lenses: either daily wear (you remove the lenses each night) or extended wear (you may sleep with them in). It's important to differentiate between wear schedule and replacement schedule — that is, how often you discard and replace your lenses.

wraparound (wrap) Type of eyeglass frame that curves around the head, from the front to the side. Wraparound sunglasses tend to offer extra sun protection because the lenses usually wrap as well. 

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