Contact lens Glossary
Amblyopia (am-blee-oh'-pee-ah): Also called "lazy eye" it is a condition where an eye has reduced vision that is not correctable with optical devices and exists without any detectable eye disease or physical abnormality. Often associated with strabismus.

Aspheric: A type of bifocal lens in which the lens power changes gradually, from the center to the periphery of the lens.
Astigmatic Keratotomy (AK): A surgical procedure to correct astigmatism by reshaping the cornea from an oval shape to a more spherical shape. Best suited for those with minimal or moderate astigmatism.

Astigmatism: Astigmatism is characterized by an irregularly shaped cornea that causes light images to focus on two separate points in the eye, producing a distorted image. Symptoms range from visual discomfort in mild cases, to severe blurring and distortion similar to a reflection in a fun-house mirror.

Automated Lamellar Keratectomy (ALK): A new procedure for extremely nearsighted patients, where only a small portion of the affected cornea is transplanted with sections from the donor cornea.

Bifocal/multifocal contact lenses: Contact lenses with two or more viewing zones, with part of the lens designed for seeing distant objects and another part for seeing near objects.

Bifocal glasses: Lenses with two viewing zones, one on top for viewing far objects and one at the bottom for viewing both near objects. Traditional bifocal glasses are generally recognized by a well-defined visible line separating the two viewing zones.

Cataract: A clouding of the crystalline lens within the eye, causing reduced visual acuity. Cataracts can be surgically removed and replaced with an intraocular lens implant to restore vision.

Color blindness: A condition where some people can see colors but experience difficulty in distinguishing between some or all colors. Technically ‘color blindness’ is an incorrect term. The correct term is "color vision deficiency." Males are affected more than women.

Contact lens: A thin plastic lens designed to fit over the cornea, usually for the correction of refractive error.

Cornea: The transparent surface that covers the pupil and iris and provides most of the eye's optical power.

Crystalline lens: The natural lens of the eye, a transparent structure suspended behind the iris. Focuses light rays on the retina and changes shape to change the focus of the eye for different distances

Daily wear contact lenses: Contact lenses designed to be worn only during waking hours; removed, disinfected and stored for the next day's use

Deposits: Accumulations of substances usually tear film components (protein), mucus, lipid, inorganic and soilant on the contact lens surface and/or in the lens material.

Depth perception: The ability to judge the relative distance of objects and the spatial relationship of objects at different distances.

Disinfecting solution: An agent that destroys surface bacteria and microorganisms on contact lenses

Disposable contact lenses: Defined by the U.S. Food and Drug Administration as a contact lens that is used one time and discarded. These can be either worn for a single day or, if they are also "extended wear" lenses, up to seven days, depending on wear schedule prescribed by the eyecare professional. Any lens that is intended to be removed from the eye, cleaned, rinsed, disinfected, and reinserted does not qualify for inclusion in this category under the FDA definition.

Emmetropia: The condition generally known as "normal vision" where light rays from distant objects are focused on the retina so that vision is sharp and clear (20/20)

Extended wear contact lenses: Contact lenses designed to be worn round-the-clock for intervals of one to seven days.

Farsightedness: See Hyperopia

Glaucoma: A condition where the pressure inside the eye is elevated to a point that can damage the optic nerve and cause blindness or a loss of peripheral vision.

Frequent & planned replacement contact lenses: General term used to refer to contact lens regimens in which lenses are replaced on a planned schedule, usually bi-weekly, monthly or quarterly.

Hyperopia (farsightedness): It is a visual defect where the light rays focus behind the retina instead of on it due to flatter cornea or shorter eyeball. People with hyperopia have difficulty seeing objects close up.

Intraocular lens (IOL): Plastic lens implanted in place of the crystalline lens (either behind cornea or behind the iris) during cataract surgery.

Iris: The round, pigmented membrane surrounding the pupil of the eye, having muscles that adjust the size of the pupil to regulate the amount of light entering the eye

LASIK: Stands for laser-assisted in situ keratomileusis. LASIK is a refractive laser eye surgery for correcting near and far sightedness and astigmatism and reduce dependency on glasses or contact lenses.

Myopia (nearsightedness): It is a visual defect where the light rays focus in front of the retina instead of on it due to steeper cornea or longer eyeball. People with this condition can see nearby objects clearly but distant objects appear blurred.

Ophthalmologist (MD): Medical doctors (MD or osteopath) uniquely trained to diagnose and treat all disorders of the eye. An ophthalmologist is trained in all aspects of eyecare--medical, surgical and optical.

Optician: A paramedical professional who manufactures and dispenses eyeglasses and helps in the selection of frames. The optician may also dispense and/or fit contact lenses, depending on individual states' licensing practices.

Optometrist (OD): State-licensed health care professionals who diagnose and treat eye health and vision problems. An OD can prescribe glasses, contact lenses, engage in low vision rehabilitation and vision therapy, have the authority to prescribe ophthalmic medications and perform certain surgical procedures. Optometrists hold the doctor of optometry (OD) degree.

Oxygen permeability: The amount of oxygen diffusing through a given amount of lens material in a given amount of time, under specified testing conditions

Presbyopia: A condition where the eye loses its ability to focus with aging. A person with presbyopia experiences difficulty and takes longer in switching between objects at different distances, such as, between the road and the speedometer when driving a car.

Photorefractive Keratotomy (PRK): A type of laser eye surgery used in some cases to correct near sightedness, far sightedness and astigmatism by reshaping the cornea.

Radial Keratotomy (RK): A surgical procedure to decrease near sightedness by making radial incisions on the eye surface with a highly precise diamond blade, which flattens the cornea for vision correction. Once very common, the surgery is now considered the riskiest of all corrective eye surgeries.

Retina: The thin nerve tissue in the back of the eye. It transforms the image received from the lens into electrical impulses that are carried to the brain for interpretation.

Rigid gas permeable lenses or RGPs: RGPs consist of a durable plastic that transmits oxygen. Because they don't contain water, RGPs resist deposits and are not prone to harboring bacteria.

Saline solution: A sterile salt solution used in cleaning, rinsing, and sometimes storing of contact lenses

Snellen chart: A standardized test chart introduced in 1862 by Dutch ophthalmologist Hermann Snellen to measure visual acuity. See visual acuity below.

Strabismus: The inability of one eye to obtain binocular vision with the fellow eye; usually due to imbalance of the muscles of the eyeball

Therapeutic contact lenses: Contact lenses designed to aid in protecting and helping a sick eye to heal. These unique lenses are frequently combined with precise medication delivery schedules to heal the eye.

Tonometry: A standard eye test that determines the fluid pressure inside the eye. Elevated pressure is a possible sign of glaucoma.

Toric lenses: Contact lenses designed to correct astigmatism by bearing two different optical powers at right angles to each other
Visual acuity: A measure of how well a person sees. It is expressed as a fraction (e.g. 20/20) where the numerator is the testing distance and the denominator is the distance at which a person with normal eyesight can read the letters on the chart. For example, if the smallest letters that the person being tested can see are on the "20/40" line, it means a person with normal eyesight can see these same letters at a testing distance of 40 feet.