An instrument to measure the field of vision.
The length of the outside line around an enclosed area.
An instrument for mapping the absolute extent of the visual field. The patient looks steadily at a target in the center of the inner surface of the hemisphere. Objects are presented on this surface and the patient says if he sees them. The edge of the visual field can be defined and any gaps in the field can be detected. There are several types of perimeter. In the static perimeter the movable object is replaced by a system of tiny lights, set in a black background, that can be flashed singly or in patterns. If the patient has a field defect he will fail to see the lights that flash in the area of the defect.
The outer edge or periphery of a body or measure of the same.