•Measures of Acuity
–20/20: can
see at 20’ what a normal person can see at 20’.
•This is normal, not perfect, vision.
– 20/200: can
see at 20’ what a normal person can see at 200’.
–Visual angle of the critical feature in a test, e.g. the
width of the bars in a grating.
•A typical population average is 1 arcmin (1/60
degree).
•Acuity and Retinal Location:
–Best at fovea.
Falls off rapidly in periphery.
Is tied to density of cones.