What is low vision? A re-evaluation of definitions

Purpose. To re-evaluate definitions of low vision, visual impairment, and d isability. Methods. We review current definitions of legal blindness and lo w vision and how these definitions are variably based on disability or impa irment, We argue for a definite distinction being made between criteria for visual impairment and visual disability, low vision being defined as the p resence of a visual impairment that results in a disability. Visual impairm ent is defined according to population norms and a statistical cut-off is u sed. Visual disability is defined by consideration of the level of visual m easures which result in measurable or reportable disability. We consider th e evidence that contrast sensitivity should be a criterion for visual disab ility in addition to visual acuity and visual field. Conclusions. According to the current information, we define visual impairment as best monocular or binocular visual acuity < (worse than) 6/7.5, total horizontal visual fi eld <146 degrees (Goldmann III-4e) or <109 degrees (III-3e), and contrast s ensitivity <1.5 (Pelli-Robson); we define visual disability as best monocul ar or binocular visual acuity <6/12 or contrast sensitivity <1.05.