Glossary of Terms

Not sure what a word means? Check out the glossary of eye terms.

Accommodating lens

As with the natural lens, an accommodating lens moves and flexes, in response to ciliary muscle contractions in the eye. These contractions drive forward movements of the lens so the eye can maintain a clear image as it focuses on near, intermediate and far objects.

Crystalens is the first and only accommodating lens approved by the FDA.


The ability of the natural crystalline lens to adjust, and with the natural contractions of the muscle in the eye, to focus on objects through a range of near, intermediate, and far distances.

Age-Related Macular Degeneration (pronounced mak-you-lar dee-jen-er-aa-shun) (AMD)

An eye condition in which the center of the retina (the macula) is slowly damaged, affecting central vision.

Amsler Grid

A chart of grid lines and a central dot used to find and check problems with central vision.


Are the nutrients that neutralize and deactivate free radicals.


In relation to glasses and contact lenses refers to the shape/design of the lenses; not quite spherical. Aspheric lenses for glasses are popular among people who have strong prescriptions because they are thin and lightweight, and reduce distortion and eye magnification.

Aspheric contact lenses can enhance optical design that creates crisp, sharp vision beyond what you are likely used to -designed to reduce halos and glare - especially at night and in low light.


A condition in which the cornea is irregularly shaped, thereby, preventing light rays to be focused so both near and distant objects appear blurred or distorted. Glasses and toric contact lenses (gas permeable and soft lenses) can correct astigmatism.


Are a clouding of the lens inside the eye so that light cannot get through to the retina.


Inflammation of the conjunctiva, characterized by a pink eye. The cause is either infectious or allergic. Other symptoms include burning, discharge, dryness, itching, light sensitivity, eye pain or discomfort, stickiness and tearing.

Contact Lens Technician

A specially trained professional, who, in many states, can fit contact lenses after an optometrist or ophthalmologist determines the prescription.


The outer, transparent, dome-like structure that covers the eye's iris, pupil, and anterior chamber. Part of the eye's focusing system that transmits and focuses light into the eye.

Daily Wear Contact Lenses

Contact lenses that are worn during waking hours but removed at the end of each day for cleaning and disinfecting.


Unit of measure for the refractive (light-bending) power of a lens; used in eyeglass and contact lens prescriptions. A negative number refers to nearsightedness; a positive number, 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

Contact lenses that are worn and then are discarded and replaced with a new lens.


Dk/t is a measurement used to quantify the amount of oxygen that is transmitted through the contact lens. The higher the Dk/t value; the higher the amount of oxygen transmitted through the lens.

Extended Wear Contact Lenses

Contact lenses that are worn while sleeping from 1 to 30 days/nights of continuous wear between removals for cleaning and disinfection or disposal.

Free Radicals

Are the unstable molecules that disrupt the structure of other molecules, resulting in damage within the eye.

Frequent/Planned Replacement Contact Lenses

Contact lenses that are worn on a daily basis with cleaning , rinsing and disinfection each time the lens is removed. The lenses are discarded after the recommended wearing period prescribed by the eye care professional.

Gas Permeable (GP) Contact Lenses

A type of contact lens that is made of a breathable, firm, durable, plastic that is custom fitted to the shape of the cornea.

Hard Contact Lenses

The first widely used type of contact lens, which was made of an inflexible plastic material called PMMA (polymethyl methacrylate). Although they provided excellent optical correction, hard lenses did not allow oxygen through the lens to reach the cornea.


A condition in which the eye is too short and flat, thereby, preventing light rays from focusing before reaching the retina. This causes an inability to see near objects clearly.

Lens (also crystalline lens)

The transparent, double convex (outward curve on both sides) structure behind the iris. Lenses help to focus light rays into the retina.


Organic compound that is oily, fatty, or waxy and commonly found in living cells. Lipids are one component of human tears, forming an oily outer layer that helps keep the eye moisturized by reducing evaporation of the watery and mucus layers beneath it. Lipids can collect on contact lenses, making them uncomfortable.


Is the part of the eye responsible for detailed central vision.


Type of eyeglass lens, intraocular lens (IOL) or contact lens design that has only one area for the eye to focus through.


Type of eyeglass lens, intraocular lens (IOL) or contact lens design that includes more than one area through which the eye focuses which allows people with presbyopia to see at multiple distances.

Myopia (also Nearsightedness)

A condition in which the eye is too long and steep, thereby causing light rays to focus before reaching the retina. This causes an inability to see distant objects clearly.


A medical doctor (MD) who specializes in diagnosing and treating eye disorders. They perform eye exams, treat disease, prescribe medication, and perform surgery. They may prescribe glasses and corrective lenses. In some states, ophthalmologists may have opticians and contact lens technicians fit contact lenses.

Optic Nerve

The nerve at the back of the eye which carries visual impulses from the retina to the brain.


Specially trained professional (not a medical doctor or optometrist) who can fill prescriptions for corrective vision by ophthalmologists and optometrists.


A doctor of optometry (OD) who has completed four years of postgraduate education. Optometrists can examine eyes for vision and health problems, and diagnose, treat, and manage many of these diseases and disorders. They can prescribe and fit eyeglasses, contact lenses, and many opthalmic medications.


Treatment for corrections, such as myopia, in which the patient wears gas permeable lenses to reshape the cornea in order to be able to see temporarily without vision correction.


Presbyopia is a natural part of getting older. In young people, the eye’s lens is soft and flexible, and readily changes shape to focus. As you age, the crystalline lens in your eye hardens and loses elasticity. With this loss of flexibility, your eyes are less able to adjust to quickly to rapid changes in focus from near to far and in-between.


Large, complex organic molecules found in all living cells. These molecules contain enzymes, antibodies, hormones and other elements that help organisms function. Proteins are present in human tears and can collect on contact lenses, resulting in discomfort and cloudy vision.


A test to determine the level of refractive errors and their correction.


The light-sensitive layer of tissue that lines the inside of the back of the eye. The retina translates the optical image into neurologic impulses that are transmitted through the optic nerve to the brain.

Rigid Gas Permeable (RGP) Contact Lenses

Type of contact lens made of breathable plastic that is custom-fit to the shape of the cornea. RGPs are the successor to hard lenses, which are now virtually obsolete.

Soft Contact Lenses

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


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.


A small red bump on the edge of the eyelid caused by an infected gland. Additional symptoms include eyelid pain, eyelid swelling, eye pain or discomfort, foreign body sensation, light sensitivity and tearing.


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