Abnormal visual acuity. The term is used to describe visual acuity substantially less than normal. The World Health Organization defines visual impairment as acuity less than 20/60 (normal being 20/20). Most states in the United States, however, will not issue an unrestricted driver's license to persons having corrected vision less than 20/40; such persons generally require special aids to read fine print and to perform other visually demanding tasks. The legal definition of blindness in the United States is visual acuity of 20/200 or worse (or severely restricted peripheral vision). The World Health Organization defines blindness as visual acuity worse than 20/400.