Perimetry

Perimetry - determination of the boundaries of the field of vision with their projection on a spherical surface. The investigation is made by means of perimeter. The basis of the device is the arc in half of circle, which you can rotate around a horizontal axis. On the outer surface of the arc caused division in degrees. When perimetric studies on the inner surface of the arcs from the centre to the periphery move in different meridians plate-and-white or color (red, green, blue) object; object size range from 1 mm2 up to 1 cm2. The study produced in a bright room or in a dark room with permanent artificial lighting arc perimeter. On a special form mark the boundaries of the field of view in accordance with the indications of the test (for the first time perception of the object).
Cm. also the Field of view.

Perimetry (from the Greek. peri - around and metreo " measure") is a method of research of the visual field. Field of view at perimetric studies projected on a concave spherical surface. This eliminates a gross distortion of peripheral boundaries of the field of view that is inevitable in projection onto the plane (Fig. 1). In 1857 Forster (C. Forster) proposed device for P. (Fig. 2).
When perimetric studies movable object moves across the blackened metal arc perimeter, the middle of which is fixed on the massive tripod and can rotate freely. The curvature radius of the arc is equal to 33 see the Subject puts his head on a special stand, located so that his eyes fixing the middle of the arc, where is a fixed fixing object appeared in the center of curvature of the arc perimeter. The second eye of the test covered with a bandage. When perimetric studies movable object (typically a white circle with diameter 2-5 mm and 10 mm) moved slowly along concave facing the observer surface arc starting
from the middle of it, where is fixed fixed object to the periphery. It is noted moment when the movable object is hidden outside the field of view of the observer. The distance from the center of fixation (in degrees) can be read on the scale on the back (convex) side of the arc perimeter. Then the movable object moves to the very end of the arc and from there gradually being to the center. It is noted the moment of appearance of an object in view. Between the vanishing points and the first appearance of the object is the boundary of the field of view of the test for the Meridian. Rotating arc perimeter every 15 degrees, mark the boundaries of the field of vision at both ends of the arc; after 12 such double definitions will be installed in the field of vision investigated. The measurement results entered in parametric form, which indicated the boundaries of normal field of vision for right and left eye (Fig. 3).
Improving the perimeter Forster was automatic registration perimeter that allows to get on the letterhead of the field of vision.
Modern models of perimeters instead of a moving object is used light Bunny, projected on the arc of a circumference. When the projection lamp is equipped with a special satanically and aperture, allowing to vary the size and brightness of the light spot. For the implementation of color perimetric studies lamp is supplied with appropriate color filters. This is the device perimeter Maggiore. Even more perfect is the perimeter of the gold-Mann, where the projection of light Bunny is not on the arc, and the concave surface of the big hemispheres, which allows precise brightness is not only a moving object, but also the background lighting. Such perimeters are used for detailed study of the field of view. In clinical practice and in the examination of bedridden patients are more simple hand-held or table perimeters built on the perimeter Forster.

Fig. 1. The scheme of the perimeter of the research field of view.
Fig. 2. Perimeter Forster.
Fig. 3. Parametric form for automatic and manual registration of sight.