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.
Axis:- The principal meridian of a cylindrical lens (in reference to contact lenses, the flattest meridian of a toric contact lens).
Base curve:- The central posterior (inside surface) curve of a contact lens. The measurement of the base curve is actually that of the radius of curvature of the sphere from which the lens is made.
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.
Cleaning solution:- Used for cleaning contact lenses. A few drops are applied to the lens’ surfaces and rubbed gently for about 20 seconds. This loosens any dirt that might have accumulated on the lens’ surfaces. The lenses are then rinsed off with a saline solution.
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
Conjunctiva: A thin, transparent membrane that lines the eyelids (palpebral conjunctiva) and the sclera (bulbar conjunctiva).
Conjunctivitis: An allergic, infectious, or chemically-induced inflammation of the conjunctiva.
Cornea
Clear front eye tissue that covers the iris and pupil and admits light. Contact lenses either fully or partially cover the cornea.
Corneal Edema: Swelling and fluid retention in the cornea, usually related to lack of sufficient oxygen in contact lens wearers
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.
Disinfectant :- A chemical that inhibits the growth of or destroys harmful microorganisms such as bacteria.
Disinfecting/soaking solution:- A solution used for disinfecting the lenses. Once the lenses have been cleaned, fill the chambers of your storage case with enough disinfecting solution to cover the lenses. Allow your lenses to soak and disinfect overnight. Always use fresh disinfecting solution.
DK value:-A measure of the oxygen transmitted by a contact lens material
Dry eye syndrome:-Dry eye usually occurs when eyes don't produce enough tears or when tears evaporate too quickly because of environmental conditions. Contact lens wearers, computer operators, post- menopausal women, and people with allergies are most susceptible to chronic dry eye.
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)
Enzyme cleaner:- An extra-strength cleaner, typically used weekly, to remove stubborn deposits from contact lenses.
EOP (Equivalent Oxygen Percentage):-A lens that is impermeable to oxygen is said to have an EOP of zero; a lens completely permeable to oxygen would have an EOP of 21 (the same as the percentage of oxygen in the atmosphere). The EOP of a contact lens falls between zero and 21, depending upon its material.
Extended wear contact lenses: Contact lenses designed to be worn round-the-clock for intervals of one to seven days.
Farsightedness: See Hyperopia (A condition where there is difficulty in seeing near objects clearly.)
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.
Monovision:-This is a contact lens fitting technique that is an alternative to bifocal glasses, bifocal contacts, or reading glasses. One eye is fitted with a contact lens for distance vision, and the other eye is fitted for near vision. Although it is an effective technique, it does have disadvantages. For example, many people who use monovision report compromised depth perception.
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.
Nearsightedness:-Also known as Myopia - a condition where there is difficulty in seeing distant objects clearly.
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.
Progressive lenses:- Like bifocals and trifocals, progressive lenses provide clear vision at all distances: near, intermediate, and far.
Pupil:-The small dark portion in the center of the eye, the pupil opens and closes to regulate the amount of light, and thus the amount of visual information, the retina receives.
Refraction:-A measurement of the eyes to determine the level of visual acuity. Most refractions are performed by optometrists, though many ophthalmologists do them as well. Refractions often result in a prescription for glasses or contact lenses.
Refractive surgery:-Any type of surgery, whether performed with a blade, laser, or waterjet, that corrects visual acuity. LASIK is a type of refractive surgery.
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.
Rewetting solution:-Drops that contact lens wearers can use all day if needed to keep the eye moist.
RGP contact lens:-Abbreviation for rigid gas permeable lens. Same as GP (gas permeable) contact lens.
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
Soft contact lens:-Made of gel-like plastic, soft contact lenses contain varying amounts of water. They provide good initial comfort for first-time wearers but must be replaced often.
Superpermeable lens:-A rigid contact lens that transmits very high amounts of oxygen
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.
