Glossary of Eye Definitions and Eye Terms.

While certainly not a complete eyecare dictionary, this Glossary of eye definitions and eye terms covers many of the common eyecare conditions, products and technologies you'll commonly discuss with your eyecare professional.

Also called lazy eye. Decreased vision in one eye that leads to the use of the other eye as the dominant eye. A problem that typically begins in childhood when external eye muscular imbalances go uncorrected.
Anti-Reflective (A/R coating):
A lens treatment for your glasses that helps to reduce distracting glare and eye fatigue by reducing the amount of light reflecting off the lens surface and making the lenses appear clearer. Your eyes will also be more visible behind the lenses.
An eye condition where the eye cannot focus light uniformly in all directions resulting from an irregular curvature of the cornea, the crystalline lens, or the eye itself. Astigmatism results in mild to moderately blurred vision and/or eyestrain.
Bi-Focal Lenses:
Lenses that use two different distinct powers in each lens, usually for near and distance correction.
A cataract is a clouding of the crystalline lens of the eye that makes it hard for light to pass through and be focused properly. In a normal eye, the crystalline lens is almost transparent, however injury, age or disease can cause the lens to eventually lose its clarity. When the lens becomes 'opaque,' it is called a cataract. Treatable by surgery.
Color deficiency:
A lack of ability to distinguish certain colors. Commonly called "color blindness", the most common form of color deficiency is the inability to distinguish shades of red and green.
Computer Vision Syndrome:
Described by the American Optometric Association as group of eye and vision-related problems associated with prolonged computer use. Symptoms include eye strain, headaches, blurred vision, dry eyes and neck and shoulder pain.
Conjunctivitis (Pinkeye):
An eye condition caused by the inflammation of the conjunctiva, or clear membrane covering the white part of the eye and lining of the eyelids. The eyes will often appear swollen and red while also feeling gritty. It is often viral and may be contagious. There are actually 20 different types of conjunctivitis – from fairly common strains that usually pose no long-term danger to you or your child's vision – to types that are resistant to antibiotics. Call or see your doctor to treat pinkeye.
The transparent, multi-layered front part of the eye that covers the pupil and iris. It provides most of the eye's optical power.
Dry Eye Syndrome:
An eye condition that presents itself as itching, burning, and irritation of the eyes, is often called "dry eye syndrome". It is one of the most common problems treated by eyecare professionals. It is usually caused by the breakdown (or deficiency) in the tears that lubricate the eyes. As we age, our bodies produce less oil to seal the eyes' watery layer. Hot, arid climates, air conditioning, certain medicines and irritants such as cigarette smoke can all increase dryness of the eye. Your eyecare professional might prescribe "artificial tears" or other eye drops to help alleviate the problem.
Floaters and Spots:
A generalized term used to describe small specks moving subtly but noticeably in your field of vision. A floater or a spot is likely a tiny clump of gel or cells in the vitreous – the clear, jelly-like fluid inside your eye. Aging, eye injury and breakdown of the vitreous are the main causes of floaters and spots. If you notice a sudden increase in the number you see, call your eyecare professional.
A tiny spot in the center of the retina that contains only cone cells. This area is responsible for our sharpness of vision.
A common cause of preventable vision loss when excessive pressure within the eye damages the optic nerve. Treatable by prescription drugs or surgery.
High(er) Index:
A dense lens material that results in thinner, lightweight lenses than standard plastic. Index refers to index refraction, which is the speed that light travels through the lens. Higher index lenses are available from 1.56 to 1.74 (the higher the number, the thinner the lens). They benefit people with stronger prescription eyeglasses.
A condition where distant objects are seen clearly, yet objects close up are seen less clearly. Also commonly referred to as "farsighted."
The pigmented (colored) membrane that lies between the cornea and the crystalline lens that controls the size of the pupil.
Crystalline Lens:
The eye's natural lens located directly behind the iris. It has the ability to change shape to focus light rays onto the retina.
The part of the retina responsible for the sharp, central vision needed to read or drive.
Macular Degeneration:
A group of conditions that include a deterioration of the macula causing a loss of central vision needed for sharp, clear eyesight. It is a leading cause of vision loss and blindness in those 65 years of age and older. Macular Degeneration is also called AMD or ARMD (age-related macular degeneration).
Minor Eye Irritation:
Slight irritation of the eye caused by a foreign body on the eye's surface such as sand, dirt or eyelashes. Wash your hands, then flush the eye with lukewarm water for up to 15 minutes. If the irritation remains and discomfort continues, seek professional medical help immediately.
Multi-Focal Lenses:
Multi-focal lenses let you focus on two or more distances through the same lens (usually distance, intermediate, and near). Also known as Bifocals, Tri-focals, Multi-focals.
A condition where distant objects appear less clearly and those objects up close are seen clearly. Also commonly referred to as "nearsighted."
Commonly called "night blindness," this is a condition that presents as impaired vision in dim light or darkness.
Optic Nerve:
A bundle of nerve fibers that carries messages from the eyes to the brain.
Photochromic lenses:
Refers to lenses that adapt to changing light in the presence of ultraviolet (UV) radiation. They return to the clear state when the UV is no longer present.
Also called "light sensitivity", this is a condition that can have many underlying causes, and can be prompted by many medications. Protection from bright light is critical for anyone with photophobia.
Plastic 1.50:
This is a lens material often used for minor prescriptions. Very few lenses are made from glass today, since glass is heavier, thicker, and can shatter. Also referred to as standard index or by the brand name CR-39.
Polarized lenses:
This type of lens includes an invisible "polarizing" filter that eliminates horizontally reflected light from reflective surfaces like water and snow for increased visual acuity (sharpness) in bright light conditions. Polarized lenses are a solution for blinding glare.
Polycarbonate lenses:
A lens material that is thinner, lighter, and more impact resistant than standard plastic. Polycarbonate lenses are the standard for children's eyewear.
Condition in which the aging crystalline lens (at around age 40) becomes less able to change shape to focus light at all distances, especially near vision. Presbyopia can be corrected with reading glasses, bifocal glasses, or progressive lenses. Additional symptoms include eyestrain, headaches, and squinting.
Bi-focal or multi-focal lenses with no visible lines where the lens power gradually changes from distance to near. Also called PALs (Progressive Addition Lenses).
A raised growth on the eye that is most often directly related to over-exposure to the sun. Dry, dusty conditions may also contribute to development of these growths. Protecting your eyes from UV radiation is a critical preventive measure.
The opening in the center of the iris that changes size to control how much light is entering the eye.
An instrument used to measure the distance between pupils. This measurement is used to position the eyeglass prescription correctly in front of the eye.
Test to determine an eye's refractive error and the best corrective lenses to be prescribed.
Part of the rear two-thirds of the eye that converts images from the eye's optical system into impulses that are transferred by the optic nerve to the brain. Consists of layers that include rods and cones.
Rods and cones:
These are cells inside the eye used by the retina to process light. Rods are used for low light levels (night vision), cones are used for sharp visual acuity and color perception.
The white part of the eye – composed of fibrous tissue that protects the inner workings of the eye.
Types of lenses that correct one vision problem, like near or far-sightedness.
Snellen Chart:
This is the commonly seen eye chart often topped by a large letter "E" used in eye examinations. This measures your eye's visual acuity, or the ability to see sharp detail clearly.
Sometimes called "crossed eyes" in young children, this condition is the lack of coordination between the eyes, such as one or both eyes turning in, out, up or down.
Ultraviolet radiation (UVR):
Commonly referred to as "UV Rays", these are light waves that consist of both UVA and UVB rays from the sun. Without proper protection, chronic exposure to UV rays can lead to various eye conditions and damage.
UV Protection:
Relates to a lens' ability to filter out harmful rays of the sun. It is recommended that glasses block 100% of both UVA and UVB rays to minimize eye damage from the sun's rays.
Variable Polarization:
A revolutionary new technology introduced by Transitions Optical and it's new Transitions® Vantage® lenses that allows the lenses to go from non-polarized indoors to polarized in the presence of UV rays. The degree of polarization also varies depending upon the presence and intensity of UV rays.
Visual Acuity:
Assessment of the eye's ability to distinguish object details and shape – numerically expressed as 20/20, 20/70, etc.