Important Low Vision Terms
20/20 vision: A measurement of visual acuity considered the mean by eye care professionals. The first 20 defines the distance in feet from the individual. The second 20 defines the distance from which a person can distinguish characters on an eye chart that is 20 feet away. People with “perfect vision” can identify characters on an eye chart from a distance of 20 feet. A person with 20/10 eyesight can see at 20 feet what a person with normal sight (20/20) can see when standing 10 feet away.
Activities of Daily Living (ADL): Daily self-care activities within an individual’s place of residence, in outdoor environments, or both. ADL include personal hygiene and grooming, dressing and undressing, self-feeding, functional transfers (getting into and out of bed or wheelchair, getting onto or off toilet), and bowel and bladder management
Adaptive Technology: Electronic magnification systems like closed circuit TVs (CCTVs) and computers.
Amblyopia: The loss or lack of development of central vision in one eye that is unrelated to any eye health problem and is not correctable with lenses. Amblyopia is commonly called “lazy eye.”
Amsler Grid: A chart used for determining potential changes in central vision and the level of impairment due to those changes. It is often used to detect and follow AMD.
Binocular: Using both eyes; also, a device designed for use with both eyes.
Cataracts: Commonly caused by aging, diabetes, and excessive exposure to UV rays, cataracts result in clouding or yellowing of the eye lens. Symptoms include blurred vision, exaggerated halos around light objects, and glare.
Contrast Sensitivity: The ability to detect differences in grayness and background. There are special tests to measure the loss of contrast which are useful in prescribing optical and non-optical devices and strategies for independent function.
Depth Perception: The ability to determine how far away an object is.
Diabetic Retinopathy: A leading cause of vision loss in persons who are diagnosed with diabetes. Diabetic retinopathy is brought on by leakage of the retinal blood vessels and can develop into progressive blurred vision, double vision, floaters, visual distortion and, ultimately, some degree of blindness.
Dry AMD: Dry AMD (Age-related Macular Degeneration) is the most common type of macular degeneration and affects 90% of the people who have the condition. In the dry form, there is a breakdown or thinning of the layer of retinal pigment epithelial cells (RPE) in the macula. It is characterized by the presence of drusen (dots of yellow crystalline deposits that develop within the macula) and thinning of the macula.
Eccentric Viewing: Not looking directly at an object, but off to its side while still paying attention to the object out of the corner of the eye. This is used when central vision has been diminished.
Functional Vision Loss: How vision loss affects the ability to function and perform activities of daily living.
Glaucoma: A sight impairment caused by unrelieved pressure inside the eye as a result of fluid build-up. Permanent impairment can range from loss of peripheral vision to severe vision loss. Symptoms include frequency of headaches, blurred vision, halos around lights, difficulty seeing in the dark, and sometimes, a non-reactive pupil, pain, or even a swollen eye.
Legal Blindness: Defined in the United States as central visual acuity of 20/200 or less, which means that what a normal sighted person can see at 200 feet, a legally blind person will see at 20 feet, or visual field restriction to 20 degrees in diameter or less (tunnel vision) in the better eye.
Low Vision Professional: An eye care or vision rehabilitation professional who is trained in the treatment of those with low vision, typically including the dispensing of low vision devices in order to maximize remaining vision.
Low Vision Services: The examination and accompanying education that lead to and determine what devices will be prescribed.
Monocular: Using one eye; also a device intended for use with one eye.
Ophthalmologist: A medical doctor (MD) specializing in the diagnosis and treatment of eye diseases to include the use of therapeutic drugs and surgical procedures.
Optician: A person who makes and sells glasses according to prescriptions prepared by an oculist, optometrist or ophthalmologist.
Optometrist: A medical professional (with a Doctor of Optometry degree, abbreviated OD) who examines and tests the eyes for disease and treats visual disorders by prescribing corrective lenses (glasses or contact lenses) and/or vision therapy. In certain states, optometrists are licensed to use diagnostic and therapeutic drugs to treat certain ocular disorders.
Orientation and Mobility: Training to help the partially-sighted get around as safely and as independently as possible.
Peripheral Vision: The opposite of central vision; in other words, the vision around the outside of the center part of the vision.
Photophobia: Discomfort and/or sensitivity to light.
Presbyopia: An eye disorder of middle age, evidenced by some minor loss of vision that exacerbates over time into more significant loss of near sight. Presbyopia could be caused by loss of the eye’s natural lens elasticity.
Retinitis Pigmentosa: This is one of the most common forms of inherited retinal degeneration with various end-results, ranging from some significant vision loss to total blindness. Symptoms include night blindness and loss of peripheral vision.
Total Blindness: The complete lack of form and visual light perception and is clinically recorded as NLP, an abbreviation for “no light perception.”
Visual Acuity: The ability to see detail (see definition of legal blindness).
Visual Field: The space in which objects are visible when the eye is in a fixed position.
Visual Perception: The ability to interpret the surrounding environment by processing information that is contained in visible light.
Wet AMD: A chronic eye disease that causes vision loss in the center of the field of vision. It is marked by swelling caused by leaking blood vessels that affect the macula. Wet macular degeneration almost always begins as dry macular degeneration.