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Visual impairment (or vision impairment) is vision
loss (of a person) to such a degree as to qualify as a
handicap through a significant limitation of visual
capability resulting from either disease, trauma, or
congenital or degenerative conditions that cannot be
corrected by conventional means, such as refractive
correction, medication, or surgery. This functional loss of
vision is typically defined to manifest with:
best corrected visual acuity of less than 20/60, or
significant central field defect,
significant peripheral field defect including homonymous or
heteronymous bilateral visual, field defect or generalized
contraction or constriction of field, or
reduced peak contrast sensitivity with either of the above
conditions.
In the United States, the terms "partially sighted," "low
vision," "legally blind," and "totally blind" are used in
the educational context to describe students with visual
impairments. They are defined as follows:
Partially sighted indicates some type of visual problem,
with a need of person to receive special education in some
cases;
Low vision generally refers to a severe visual impairment,
not necessarily limited to distance vision. Low vision
applies to all individuals with sight who are unable to read
the newspaper at a normal viewing distance, even with the
aid of eyeglasses or contact lenses. They use a combination
of vision and other senses to learn, although they may
require adaptations in lighting or the size of print, and,
sometimes, Braille;
Myopic - unable to see distant objects clearly, commonly
called near-sighted or short-sighted
Hyperopic - unable to see close objects clearly, commonly
called far-sighted or long-sighted
Legally blind indicates that a person has less than 20/200
vision in the better eye after best correction (contact
lenses or glasses), or a field of vision of less than 20
degrees in the better eye; and
Totally blind students learn via Braille or other non-visual
media.
Visual impairment is the consequence of a functional loss of
vision, rather than the eye disorder itself. Eye disorders
which can lead to visual impairments can include retinal
degeneration, albinism, cataracts, glaucoma, muscular
problems that result in visual disturbances, corneal
disorders, diabetic retinopathy, congenital disorders, and
infection." Visual impairment can also be caused by brain
and nerve disorders, in which case it is usually termed
cortical visual impairment (CVI).
The American Medical Association's Guides to the Evaluation
of Permanent Impairment attempts to provide "a standardized,
objective approach to evaluating medical impairments." The
Visual System chapter "provides criteria for evaluating
permanent impairment of the visual system as it affects an
individual's ability to perform activities of daily living."
The Guide has estimated that the loss of one eye equals 25%
impairment of the visual system and 24% impairment of the
whole person; total loss of vision in both eyes is
considered to be 100% visual impairment and 85% impairment
of the whole person.
Visual impairments have considerable economic impact on even
developed countries.
Visual impairment is one of the potential dangers of
ultraviolet germicidal irradiation.
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