Last reviewed 01/2018

Perimetry is the quantification of the extent of the visual fields with a perimeter apparatus.

Manual and computerised machines are used, but both work on the same following principles:

  • the patient sits opposite the machine and places their head on a fixed rest so as to provide a constant position for visualisation of targets
  • the patient closes, or has patched, one eye
  • with the other eye they focus on the central hub of the instrument while a dot of light moves in on successive meridians
  • they are asked to give a response - e.g. verbal or pressing a button - when the target is first seen
  • the meridians are changed so that the whole field is mapped on perimetry paper, and successive maps can be drawn with lights of different colours and sizes
  • the other eye is tested in the same way