Medical Dictionary Definitions A-Z List
Medical Dictionary Definitions A - Z - «V»:
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Visual acuity
Visual acuity: The clarity or clearness of the vision, a
measure of how well a person sees. The ability to distinguish details
and shapes of objects; also called central vision.
The word "acuity" comes from the Latin "acuitas" = sharpness....
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Visual acuity test
Visual acuity test: This test measures how well you see at various distances. It is the familiar eye chart test.
The eye chart itself -- the usual one is called Snellen's chart -- is imprinted with block letters that line-by-line decrease in size, corresponding to the distance at which that line o...
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Visual contrast sensitivity
Visual contrast sensitivity: The ability to perceive differences between an object and its background....
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Visual evoked response
Visual evoked response: VER. A type of electrophysiologic retinal testing done to measure the electrical potential resulting from a visual stimulus....
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Visual field
Visual field: The entire area that can be seen when the eye
is directed forward, including that which is seen with peripheral
vision.
The visual field can be tested to measure the extent and
distribution of the field of vision. The test may be done by a number
of methods including what are terme...
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Visual field test
Visual field test: A test which measures the extent and distribution of the field of vision.
The visual field test may be done by a number of methods including what are termed confrontation, tangent screen exam and automated perimetry.
Although the test may seem tedious, it is not painful or uncomf...
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Visual nerve pathways
Visual nerve pathways: The optic nerves serving the eyes join behind the eyes just in front of the pituitary gland to form a cross-shaped structure called the optic chiasma.
Within the optic chiasma some of the nerve fibers cross. The fibers from the nasal (inside) half of each retina cross over, bu...
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Visual pathway glioma
Visual pathway glioma: A slow-growing benign tumor of the eye....
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Visual receptor
Visual receptor: The layer of rods and cones that are the visual cells of the retina....
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Vital
Vital: Necessary to maintain life. Breathing is a vital function....
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Vital bodily function
Vital bodily function: 1. An essential bodily function.
2. A key function for life.
3. A function required by most, if not all, people.
The definition of vital bodily functions is prerequisite to the determination of death. But what are the vital bodily functions? Do they include cerebral function...
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Vitamin A
Vitamin A: Vitamin A is retinol. Carotene compounds
(found, for example, in egg yolk, butter and cream) are gradually
converted by the body to vitamin A (retinol). A form of vitamin A
called retinal is responsible for transmitting light sensation in the
retina of the eye. Deficiency of vitamin A...
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Vitamin A deficiency
Vitamin A deficiency: A lack of vitamin A.
Vitamin A deficiency (VAD) occurs where diets contain insufficient
vitamin A for meeting the needs associated with growth and
development, physiological functions, and periods of added stress due
to illness. Infections such as measles may precipitate a c...
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Vitamin B -- niacin
Vitamin B -- niacin: Deficiency of
niacin, one of the B-complex vitamins, causes pellagra. See: Pellagra....
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Vitamin B -- nicotinic acid
Vitamin B -- nicotinic acid: Deficiency of nicotinic acid (also known as niacin), one of the B-complex vitamins, causes pellagra.
Pellagra was known as the "disease of the four D's" -- dermatitis,
diarrhea, dementia and death. The disease is specifically
characterized by:
Dermatitis: A rash on ...
