PERIMETER

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This is for testing the field of vision. The subject places his chin on a rest and the eye to be tested is focused on a white disc in the centre of the apparatus. A second fixation target is slowly moved in from the periphery of vision and the subject indicates when he first sees it. By moving the second object in from various directions it is possible to map the field of vision. Various refinements on the basic instruments are available including automatic mapping, and circuits to detect if the eye wanders from the main fixation target. The visual field is drawn as a set of isopters for different target size, intensity, or colour.