The numbers show the visual field quality, the bigger the number, the better the vision
Lower numbers have darker shades, showing areas with poor vision. Black areas (with 0 value) show areas with no vision at all.
White areas indicate perfect vision.
A healthy eye will show a vision field with most values between 20 and 30, a few 40's and only one or two 0's, showing the normal blind spot.
See also: Visual Field Map.