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Glossary of Eye Care Terms

Amblyopia: Commonly referred to as "lazy eye". This condition is described as decreased vision in one eye which causes the other eye to take over and process most of the vision.  This condition occurs most commonly in young children.
 
Anti-Reflective (A/R coating): A lens treatment for eyeglasses 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.
 
Astigmatism: 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 severe blurred vision and/or eyestrain.
 
Bi-Focal Lens: A lens which uses two different distinct powers in the lens.  One is usually for near, and the other for distance correction.
 
Cataracts: A cataract is a clouding of the crystalline lens of the eye.  When this occurs, it becomes difficult for light to pass through the lens and be focused properly on the retina.  In a normal eye, the crystalline lens is almost 100% transparent.  Either from an eye injury, age, or disease the lens eventually loses its transparency. When the lens becomes "cloudy" it is called a cataract.  When the cataract becomes advanced, surgery can correct it.  
 
Color deficiency: A lack of ability to distinguish certain colors.  The most common form of color deficiency is the inability to distinguish shades of red and green.
 
Conjunctivitis: A common type of conjunctivitis is called "pink eye".  Conjunctivitis is 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.  Some from fairly common strains that usually pose no long term danger to types that can be resistant to antibiotics.
 
Cornea: The transparent, multi-layered front part of the eye that covers the pupil and iris. It provides most of the eye’s refractive power.  Sometimes referred to as the "window" of the eye. 
 
Dry Eye Syndrome: An eye condition that can present itself as itching, burning, gritty feeling, and/or irritation of the eyes.  It is one of the most common problems treated by eye care professionals. It is usually caused by the breakdown, or a deficiency, in the tears which lubricate the eyes. As we age, our bodies produce less and less tears.  Hot, arid climates, air conditioning, certain medications, and irritants such as cigarette smoke can all increase dryness of the eye.  Dry eye syndrome can be managed and treated several different ways. 
 
Floaters and Spots: A generalized term used to describe small specks moving subtly throughout your field of vision. A floater or a spot is likely a tiny clump of gel or cells in the vitreous fluid.  This fluid is the clear, "jelly-like" fluid inside your eye. Aging, eye injury, and breakdown of the vitreous are the main causes of floaters and spots. 
 
Fovea: A tiny spot in the center of the retina that contains only cone cells. This area is responsible for our most central, detailed vision.
 
Glaucoma: When excessive pressure within the eye damages the optic nerve. Treatable by prescription drugs or surgery.
 
High Index: A lens material that results in thinner, more lightweight lenses than standard plastic.  These lenses will benefit people with stronger prescription eyeglasses.
 
Hyperopia: A condition where distant objects are seen clearly while objects close up are seen less clearly. Also commonly referred to as “farsightedness". 
 
Iris: The colored portion of the eye that lies between the cornea and the crystalline lens.  The iris 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.
 
Macula: The part of the retina responsible for sharp, detailed, central vision.
 
Macular Degeneration: A group of conditions that include a deterioration of the macula.  This causes a loss of central vision.  Macular degeneration is a leading cause of vision loss in those 65 years of age and older. Macular degeneration is also called AMD or ARMD (age-related macular degeneration).
 
Multi-Focal Lenses: Multi-focal lenses allow for the ability to focus on two or more distances through the same lens.  These lenses usually provide vision at a distance, middle, and near.  These are also known as bifocals or trifocals.
 
Myopia: A condition where distant objects appear less clearly while objects up close are seen clearly. Also commonly referred to as “nearsightedness". 
 
Nyctalopia: 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 automatically change from clear to dark in the presence of ultraviolet (UV) radiation.
 
Photophobia: Also called “light sensitivity".  This condition can have many underlying causes, and can also be prompted by many medications. Protection from bright light is critical for anyone with photophobia.
 
Plastic: This is a lens material also called CR-39.  Very few lenses today are made from glass because glass is heavier, thicker, and can shatter.  Plastic or other lens materials are better options. 
 
Polarized lenses: A type of lens that filters light to decrease the amount glare from reflective surfaces like water and snow.  These lenses will increase visual acuity or sharpness in your vision in bright light conditions.
 
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.
 
Presbyopia: Condition in which the aging crystalline lens, usually around age 40, becomes less able to change shape to focus light.  This causes vision at near tasks to become difficult.  Presbyopia is most commonly corrected with either eyeglasses or contact lenses utilizing bifocal or multifocal lenses. 
 
Progressive lenses: PALs or progressive addition lenses are bifocal or trifocal lenses with no visible lines.  The lens power gradually changes from distance to near while correcting for distance, middle, and near vision. 
 
Pterygium: A raised growth on the eye that is most often directly related to over-exposure to the sun's UV radiation.  Dry, dusty conditions may exacerbate the symptoms and sometimes cause redness and pain.  Protecting your eyes from UV radiation is a critical preventive measure.
 
Pupil: The opening in the center of the iris that changes size to control how much light is entering the eye.
 
Pupillometer: An instrument used to measure the distance between pupils. This measurement is used to position the eyeglass prescription correctly in front of the eye.
 
Refraction: Test to determine an eye’s refractive error and the best corrective lenses to be prescribed.
 
Retina: 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 and night vision.  While cones are used for light, sharp visual acuity, and color perception.
 
Sclera: The white part of the eye that is composed of fibrous tissue to protect the inner workings of the eye.
 
Single-Vision: A type of lens that corrects one vision problem.  For example, nearsightedness or farsightedness.
 
Snellen Chart: This is the commonly seen eye chart used during eye examinations. This measures the eye’s visual acuity. 
 
Strabismus: Also know as “crossed eyes” in young children.  This condition is the lack of coordination between the eyes where one or both eyes turn 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 lenses block 100% of both UVA and UVB rays to minimize eye damage from the sun’s rays.
 
Visual Acuity: Assessment of the eye’s ability to distinguish object details and shape.  The measurement is expressed numerically as 20/20, 20/70, 20/200, etc.