Visual impairment (or vision impairment) is a decreased ability to see to a degree that causes problems not fixable by usual means, such as glasses or medication. It can be due to disease, trauma, or congenital or degenerative conditions. This loss of vision is typically defined as 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. 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;Eye Trauma Epidemiology and Prevention 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. ‘A major proportion of global visual impairment is preventable’. An update based on census data of 2010 in the United States projects that 13 million Americans aged 40 and older will have a visual impairment or be blind by the year 2050.
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