uMeasures
of Acuity
l20/20: can
see at 20’ what a normal person can see at 20’.
uThis
is normal, not perfect, vision.
l 20/200: can
see at 20’ what a normal person can see at 200’.
lVisual
angle of the critical feature in a test, e.g. the width of the
bars in a grating.
uA
typical population average is 1 arcmin (1/60 degree).
uAcuity
and Retinal Location:
lBest
at fovea. Falls off rapidly in
periphery. Is tied to density
of cones.