Glossary of Terms

Navigating the language of eye care and eye problems can be challenging. The Center for Vision Loss has developed this basic glossary for informational purposes only. It is not meant to take the place of visiting your eye doctor annually to receive professional advice to diagnose or treat an eye health problem.

Age-Related Macular Degeneration—this degenerative eye disease causes damage to the macula of the eye. People affected with age-related macular degeneration (AMD) have problems reading, driving and performing activities that require clear central vision. AMD is the leading cause of vision loss in the senior population and has two stages: dry and wet. In the dry stage the delicate tissues of the macula become thinned and slowly lose function. This is the more common form. The wet stage is caused by the growth of abnormal blood vessels which tend to leak or hemorrhage resulting in the formation of scar tissue. This is the less common form of AMD but also the most damaging.

Amblyopia—the most common eye problem that causes poor vision in children and is often called “lazy eye.” The problem occurs when the pathways that carry vision messages from one of the eyes to the brain don’t grow strong enough causing the brain to favor the good eye. The weaker eye then needs to be made stronger so that it can function normally. Eye patching, surgery or special glasses may be prescribed.

Cataract—a clouding of the eye’s lens. The majority of cataracts are related to age. Most people do not even realize they have a cataract as cataracts grow slowly and may not affect vision early on. Surgery is the only treatment.

Charles Bonnet Syndrome (CBS)—this is a little known manifestation of vision loss that is experienced by some people with visual impairment. It consists of visual hallucinations that can seem very real. People with CBS may see hallucinations of patterns and lines which can become quite intricate. Or they may also see more complicated images of people, places, landscapes and groups of people sometimes life size and other times in miniature. These images appear out of the blue and can continue for a few minutes or sometimes several hours. CBS generally affects people who have lost their sight later in life. In addition, many times this condition is not talked about because of the anxiety it causes regarding mental illness.

Diabetic Retinopathy—a complication of diabetes that is caused by changes in the blood vessels of the retina. When blood vessels in the retina are damaged, they may leak blood and grow fragile, brush-like branches and damage tissue. This blurs or distorts the vision images that the retina sends to the brain. Diabetic eye disease is the leading cause of blindness in the United States.

Glaucoma—a group of eye diseases causing optic nerve damage. In glaucoma, eye pressure plays a role in damaging the nerve fibers of the optic nerve. When a significant number of nerve fibers are damaged, blind spots develop in the field of vision. If the entire nerve is damaged, blindness results. Glaucoma is the leading cause of blindness in the world. Early detection and treatment by an ophthalmologist is the key to preventing optic nerve damage and vision loss from glaucoma.

Hyperopia—or farsightedness, is an abnormal condition of the eye in which vision is better for distant objects than for near objects. It can be corrected with eye glasses and contact lenses.

Legal Blindness—occurs when the best corrected acuity is less than 20/200 in the better eye and/or a person’s side, or peripheral, vision is restricted to 20 degrees or less in the better eye. Some useful vision may remain, however. If you are legally blind, you may qualify for certain government benefits.

Low Vision—a level of vision below normal (20/70 or less) that cannot be corrected with conventional glasses or contact lenses. Low vision is not the same as blindness. People with low vision can use their remaining sight, however, low vision may interfere with the performance of daily activities.

Low Vision Specialist—a licensed ophthalmologist or optometrist who is skilled in the examination, treatment and management of patients with visual impairments that are not treatable by medical, surgical or conventional use of eyewear or contact lenses. The Low Vision Specialist is able to define the extent of an individual’s functional level of vision and then recommend low vision aids and devices to help use that remaining sight.

Myopia—also known as nearsightedness, an eye disorder rather than an eye disease in which the patient has difficulty seeing distant objects. Myopia is commonly treated using eye glasses or contact lenses.

Optician—this eye care professional designs, finishes, fits and dispenses eye glasses and contact lenses based on an eye doctor’s prescription.

Ophthalmologist—a physician (doctor of medicine or doctor of osteopathy) who is qualified by lengthy medical education, training and experience to provide total eye care including vision services, contact lenses, eye exams, medical eye care and surgical eye care and is licensed by a state regulatory board to practice medicine and surgery.

Optometrist—a health care professional who has earned the degree of doctor of optometry (OD) and is trained and state licensed to provide primary eye care services including eye health and vision exams; diagnosis and treatment of eye diseases and vision disorders; and the prescription of glasses, contact lenses, low vision rehabilitation, vision therapy and medications.

Presbyopia—an eye condition that occurs as part of the normal aging process over a number of years. It manifests itself as the loss of the eye’s ability to focus on close objects.

Snellen Chart—the test chart used to assess visual acuity which contains rows of letters, numbers or symbols in standardized graded sizes.

Visual Acuity—the measure of the eye’s ability to distinguish the smallest identifiable letter or symbol, its details and shape, usually at a distance of 20 feet. This measurement is usually given as a fraction. The top number is the testing distance and the bottom number is the distance from which a normal eye can see the shape or letter. Perfect vision is 20/20. If your vision is 20/60, you can see at a distance of 20 feet what someone with perfect vision can see at 60 feet.

Visual Impairment—occurs when neither of your eyes can see better than 20/60 without improvement from glasses or contact lenses. Poor night vision, limited side vision, double vision, and loss of vision in one eye may also determine visual impairment.

Strabismus—an eye condition in children which causes one or both eyes to turn inward (“crossed eyes”), outward (“wall eyes”), upward or downward. The resulting vision is not clear and needs to be corrected as early as possible.

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