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Glossary of Terms

Amblyopia Decreased vision in an eye that is not correctable with optical devices and that exists without detectable disease or physical abnormality to the eye or visual pathway. Often associated with strabismus.

Aspheric A type of bifocal lens in which the lens power changes gradually, from the center to the edge of the lens

Astigmatic Keratotomy (AK) is a surgical procedure performed to correct astigmatism. To correct astigmatism, the number, angle, and distribution of the incisions will vary from patient to patient, depending upon the degree and axis (location) of the astigmatism.

Astigmatism Astigmatism is characterized by an irregularly shaped cornea that causes light images to focus on two separate points in the eye, creating 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) is a relatively new procedure performed for extremely nearsighted patients. In this procedure, a flap of corneal surface tissue is folded back, a layer of the central corneal tissue is removed, and the surface flap is replaced.

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 Spectacles with two viewing zones, one on top and one on the bottom for seeing both near and far objects. Traditional bifocal glasses are generally recognized by a well-defined visible line separating the two viewing zones. Invented in 1784 by Benjamin Franklin.

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, restoring vision.

Color blindness A nonspecific term for congenital or acquired impairment of color discrimination. Technically it is an incorrect term, as most individuals who are color "blind" see colors; they just have difficulty distinguishing certain colors from others. A more precise term is "color vision deficiency." It seems that more males are affected, with 7% of males showing this deficiency, and only about 0.5% of females. Color vision deficiency is not a disease or degenerative condition, though occasionally an acquired color vision deficiency may be a symptom of other health problems.

Contact lens A thin plastic lens designed to fit over the cornea, usually for the correction of refractive error. Click here for more information on the TYPES and BENEFITS on contact lenses.

Cornea The transparent surface that covers the pupil and iris (like a watch crystal), and provides most of the eye's optical power. Contact lenses are worn over the corneal surface.

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), onto the contact lens surface and/or in the lens material. Types include protein, mucus, lipid, inorganic and soilant. See solution.

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 kills 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 in which the pressure inside the eye is elevated to a point that can damage the optic nerve and cause a loss of peripheral vision, or blindness. Read more.

Frequent & planned replacement contact lenses General term used to refer to contact lens regimens in which lenses are replaced on a planned schedule, most often every two weeks, monthly or quarterly.

Hyperopia (farsightedness) Hyperopia occurs when the eyeball is too short from front to back, or the eye's focusing mechanism is too weak, causing light rays to be focused behind, rather than on the retina. 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 Acronym for Laser-Assisted in Situ Keratomileusis. LASIK is a kind of laser eye surgery designed to improve focus by altering the shape of the cornea. To perform the procedure, a qualified ophthalmologist uses a microkeratome to cut a circular "protective" flap to expose the inner layers of the cornea, which are reshaped with the laser. This procedure has been dubbed "flap-and-zap". To complete the procedure, the ophthalmologist then repositions the flap. This last step is important, for if done incorrectly, it can lead to scarring and optical distortion.

Myopia (nearsightedness) Myopia is a condition which occurs when the eyeball is too long, or the eye's focusing mechanism is too powerful (cornea and lens), and light rays are focused in front of the retina. People with this condition can see clearly up close but not at a distance.

Ophthalmologist 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 This is a condition that occurs as the eye's lens grows older and begins to lose some of the elasticity needed to switch focus between viewing near and far objects. Also known as "aging eye," presbyopia actually starts at about age 10, although most people do not begin to experience the effects of presbyopia until their forties. As the eye's lens continues to lose its elasticity, the eye takes longer to adjust between objects such as the road and the speedometer. For more on presbyopia, click here.

Photorefractive Keratotomy (PRK) Using an excimer laser with power controlled by computer, PRK is designed to change the shape of the cornea to reduce vision problems. The laser vaporizes microscopic slivers from the outer layer of the cornea to flatten it. The flattening of the cornea is intended to correct myopia (nearsightedness) and astigmatism (uneven curvature of the cornea that distorts vision).

Radial Keratotomy (RK) Once the most common type of refractive surgery, RK is now considered the riskiest of all corrective eye surgeries. During RK surgery, a number of spoke-like incisions are made on the surface of the eye with a small diamond-tipped blade to flatten the cornea so light rays focus directly on the retina. The procedure is designed to correct or reduce nearsightedness.

Retina The thin nerve tissue in the back of the eye. It receives an image from the lens, and transforms this image into electrical impulses that are carried by the optic nerve to the brain for interpretation.

Rigid gas permeable lenses 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. Visual acuity is expressed as a fraction (e.g. 20/20) in which the numerator denotes the testing distance and the denominator indicates 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.

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 Expressed as a fraction (e.g. 20/20) in which the numerator denotes the testing distance and the denominator indicates the distance at which a person with normal eyesight can resolve the letters on the chart

Acuvue 2
Acuvue Advance
Acuvue Advance +
Acuvue Oasys
Biomedics 38
Biomedics 55
Biomedics XC
Boston II
Boston IV
Boston Envision
Boston Equalens
Boston EO
Boston ES
Boston XO
CIBA Vision
ClearSight Toric
ClearView Custom
Fluoroperm 92
Frequency 38
FreshLook Colors
FreshLook Toric
FreshLook Radiance
Focus Progressive
Focus Softcolors
Focus Toric
Focus Visitint
Hydrasoft Toric
Paragon Thin
Proclear Multifocal
Proclear Sphere
Proclear Toric
PureVision Multi
PureVision Toric
Soflens 38
SofLens Daily Disp
SofLens Multi-Focal
TruColour Elite
Vision Care 2
Zero 4
Zero 6

Contact Lenses are prescription medical devices. Even if worn only for cosmetic reasons they must be prescribed and properly fitted by an eye care professional. Always follow the care and cleaning guidelines. Remove your contacts immediately if you experience any redness or discomfort and notify your eye care doctor immediately. Have regular eye exams. Never swap lenses with another person. This can potentially lead to infection and possibly serious complications.

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