Vision impairment

**Definition:** A vision impairment results when an eye condition affects the visual system and one or more of its vision functions. Typically, population-based surveys measure visual impairment using exclusively visual acuity, with severity categorized as mild, moderate or severe distance vision impairment or blindness, and near vision impairment. However, in the clinical setting, other visual functions are also often assessed, such as a person’s field of vision, contrast sensitivity and colour vision.