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.