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Eye Health Glossary


Legal blindness: Having visual acuity that, in both eyes, can't be corrected to better than 20/200 or has a visual field of 20 degrees or less (tunnel vision) remaining.

Low vision: A condition in which a person is either legally blind (visual acuity of less than 20/200 or tunnel vision) or visual acuity between 20/70 and 20/200 despite the use of conventional corrections such as prescription eyeglasses.

Macula: The central portion of the retina, a healthy macula is critical in maintaining sharp vision.

Macular edema: A swelling of the macula that can cause vision to become blurred or impaired. It is usually caused by an injury or disease.

Myopia: A condition in which a person has difficulty seeing objects in the distance. Myopia is commonly referred to as nearsightedness.

Night blindness: A condition in which a person has impaired vision in dim or darkened conditions. Night blindness is commonly caused by a deficiency in vitamin A or, less commonly, by retinitis pigmentosa.

Nyctalopia: See night blindness.

Ocular: Of or relating to the eye.

Ophthalmologist: Ophthalmologists are doctors who specialize in the medical and surgical care of the eyes and visual system and also the prevention of eye disease and injury. They can be either doctors of medicine (MD) that graduate from a medical school or doctors of osteopathy (DO) who graduate from osteopathy school. As a qualified specialist, an ophthalmologist is qualified to deliver total eye care, meaning vision services, eye exams, medical and surgical eye care, diagnosis and treatment of disease, and management of visual complications that are caused by other conditions, like diabetes.

Ophthalmoscope: An instrument used to examine the retina. There are two types of ophthalmoscopes: direct and indirect. The direct version is used to examine the center of the retina, while the indirect is used when an exam of the entire retina is needed.

Optic nerve: The nerve that connects the eye to the brain. The optic nerve carries impulses of light from the retina to the brain, which then interprets the impulses as images.

Optometrist: A doctor trained to examine, diagnose, treat, and manage some diseases and disorders of the eye. Like ophthalmologists, optometrists are trained to examine the internal and external structure of the eyes to detect diseases such as glaucoma, retinal diseases, and cataracts. Optometrists do not perform surgery and are not trained to care for and manage all diseases and disorders of the eyes. The optometrist is trained to diagnose and treat vision conditions like nearsightedness, farsightedness, astigmatism, and presbyopia.

Peripheral vision: The region of sight where we see objects to the side, out of our direct line of vision.

Photocoagulation: A surgical procedure in which a laser is used to stop bleeding blood vessels or to repair damaged tissue. Photocoagulation can also be used to help treat a tumor found in the eye.

WebMD Medical Reference

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