2010 BC Guide in Determining Fitness to Drive

Visual field impairment refers to a loss of part of the normal visual field. The term “scotoma”refers to any area where the area of lost visual field is surrounded by normal vision. See 21.17for more information on types of visual field impairments.Common vision impairmentsBlindness/low visionTotal blindness is the complete lack of vision and is often described as no light perception. Aperson may be considered ‘blind’ even though they have some vision. There is no universallyaccepted level of visual acuity to define blindness. In North America and most of Europe aperson is considered to be legally blind if their visual acuity is 20/200 (6/60) or less in the bettereye with the best correction possible, or if their visual field is less than 20 degrees in diameter.The World Health Organization (WHO) defines “low vision” as visual acuity between 20/60(6/18) and 20/400 (6/120) or a visual field between 10 and 20 degrees in diameter. The WHOdefinition of “blindness” is visual acuity less than 20/400 (3/60) or a visual field less than 10degrees.Myopia, hyperopia, and astigmatism (refractive errors)Myopia, hyperopia, and astigmatism are conditions associated with reduced visual acuity. Theyare known as refractive errors and are the result of errors in the focusing of light by the eye.Myopia (nearsightedness) is a condition in which near objects are seen clearly but distant objectsdo not come into proper focus. Individuals with normal daytime vision may experience “nightmyopia”. Night myopia is believed to be caused by pupils dilating to let more light in, whichadds aberrations that result in nearsightedness. It is more common in younger individuals anpeople who are myopic.Hyperopia (farsightedness) is a condition in which distant objects are seen clearly but closeobjects do not come into focus. Age-related farsightedness is called presbyopia. It is not adisease, but occurs as a natural part of the aging process of the eye and usually becomesnoticeable as an individual enters their early to mid-40’s.Astigmatism is a visual condition that results in blurred vision. It commonly occurs with otherconditions such as myopia and hyperopia.Monocular vision/Loss of stereoscopic depth perceptionMonocular vision refers to having vision in one eye only and is associated with the loss ofstereoscopic vision. Stereoscopic vision, in which the brain processes information from each eyeto create a single visual image, is integral to depth perception in those with binocular vision.253