Visual impairment is mostly referred to as a loss of sight that interferes with daily living tasks when special adaptations are not made. The major factors that define one's vision (or vision impairmnet) are vision acuity and visual field. Vision acuity defines how clear a person sees. For example, a person with a 20/70 vision acuity sees things from a 20 feet distance a normal person can see from 70 feet. Visual field refers to how widespread someone's vision is.
The World Health Organisation (WHO) defines visual impairment as a vision acuity (with the best possible correction) of less than 20/70 or a visual field of less than 20 degrees and blindness as a visual acuity of less than 20/400 or a visual field of less than 10 degrees. Sighted people have a visual field of about 170 degrees. In the U.S. the term "legally blind" is used to describe people with a visual acuit of less than 20/200 or a visual field of 20 degrees or less. Legal blindness means that a person is eligible for certain services.
What Causes Visual Impairment?
There are lots of different causes for blindness or visual impairment. Some disorders are congenital (ie. someone is born with it), but a person may also become visually impaired or blind later in life. Genetics, birth complications, infections (eg. Trachoma) or accidents may cause vision loss. As people age, chances for visual impairment also increase.
How Common Is Vision Impairment?
Approximately 1,1 million Americans are blind, among which about 93000 children. The majority of people with visual impairment (about 60%) are over age 60.
Is There Any Equipment to Help the Blind?
As technological knowledge improves, more and more equipment is designed to make life easier for everyone, and also h=more equipment is designed to help the blind. Nowadays, the blind can use a computer due to adaptations such as a braille display or speech software. Adaptive equipment for daily living is made and improvements are made to mobility equipment and Braille, so that blind and visually impaired people can live more independently.
