Pub. date: 2005 | Online Pub. Date: September 15, 2007 | DOI: 10.4135/9781412950565 | Print ISBN: 9780761928201 | Online ISBN: 9781412950565| Publisher:SAGE Publications, Inc.About this encyclopedia
Visual Impairment across the Life Span
Susan M. Bruce
Visual impairment is a broad term used to describe vision loss in individuals who are totally blind, functionally blind, or legally blind, or who have low vision. Like those who are totally blind, individuals with functional blindness will rely on the auditory and tactile senses for learning. Legal blindness is defined as central acuity of 20/200 or less with best correction, or less than 20 degrees of visual field remaining (normal visual field is about 160 degrees). Acuity measures such as 20/200 report the individual's distance vision as compared with the normal visual acuity of 20/20. Therefore, 20/200 means that what a person with normal vision could recognize at 200 feet would need to be viewed at 20 feet by an individual with legal blindness. The term low vision is used to describe vision that is measured between 20/70 and 20/200. Low vision is used as the minimal criterion congenital ...