Visual impairment

Visual impairment can be defined as any chronic visual deficit that impairs everyday functioning and is not correctable by ordinary eyeglasses or contact lenses. Visual impairment can be mild or moderate but also includes total blindness or functional blindness where no useful vision remains. Although there have been important strides over the past few decades in the treatment and prevention of eye diseases that cause visual impairment, there are still many causes of vision loss for which there is no cure. Even with the best medical treatment, many Americans live with impaired vision. In the United States, where normal vision is 20/20, legal blindness is defined as visual acuity with best correction in the better eye worse than or equal to 20/200 or a visual field extent of less than 20 degrees in diameter. In many States, a visual acuity of less than 20/40 disqualifies a person from obtaining a driver's license, as do some visual field deficits. Research in visual impairment and blindness is aimed at developing and assessing new methods for the rehabilitation of visually impaired individuals through assistive technologies, training, and rehabilitation services and education.

Current estimates of the number of people who are visually impaired vary greatly by source and method of measurement, as well as by the inclusion criteria applied. Conservative estimates suggest that there are at least 3.5 to 5 million Americans who are visually impaired, and more than 1 million of these are legally blind. Because of the narrowly defined definitions of visual impairment, these figures undoubtedly underestimate the problem. However, many people experience functional limitations due to vision loss even though they do not meet the criteria for legal blindness. Even relatively mild impairment of vision can affect the performance of everyday tasks such as driving, reading, and walking. When more broadly defined as visual problems that hamper the performance and enjoyment of everyday activities, other recent estimates indicate that almost 14 million Americans suffer from visual impairment. Older adults represent the majority of the visually impaired population. Visual impairment is included among the 10 most prevalent causes of disability in the United States.

The leading causes of visual impairment are diseases that are common in elderly persons, including AMD, glaucoma, DR, cataract, and optic nerve atrophy. More than two-thirds of people with visual impairment are older than 65 years of age. It is estimated that there were almost 34 million Americans older than age 65 years in 1992 and that by 2030 this number will more than double. Visual impairment in elderly persons decreases independence, increases the risk of falls and fractures, and often leads to isolation and depression.

The leading causes of visual impairment in infants and children are retinopathy of prematurity, deficits in the visual centers of the brain, and structural ocular abnormalities such as cataract and retinal abnormalities. These conditions sometimes have a severe impact on children's quality of life, especially when vision impairment coexists with other impairments, and can have major consequences on education and future opportunities for employment. However, children, like adults, benefit significantly from coordinated and comprehensive services to ameliorate disability.