What is Perimetry?
Our visual world is composed of images of colours, textures, edges and contrasts. In addition, these images may be moving or flickering. The goal of visual testing is to quantitate of these functions.
Traditionally we have tested visual function as visual acuity - the capacity to discriminate the fine details of objects and visual field - the portion of space in which objects are visible at the same moment during steady fixation of gaze in one direction. Colour vision testing, flicker sensitivity, contrast sensitivity, pupillary responses and motion testing are some of the other methods of quantitating vision.
Perimetry is the systematic measurement
of visual field function. Left
is an example of typical field loss of someone with
Left is an example of typical field loss of someone with glaucoma.
With threshold static automated perimetry, a computer program is selected. The most commonly used one tests the central 30° of the visual field using a six degree spaced grid. This is accomplished by keeping the size and location of a target constant and varying the brightness until the dimmest target the patient can see at each of the test locations is found. These maps of visual sensitivity, made by either of these methods, are very important in diagnosing diseases of the visual system. Different patterns of visual loss are found with diseases of the eye, optic nerve central nervous system.
This is an example of a field
defect of someone who has had a stroke and suffered a
This is an example of a field defect of someone who has had a stroke and suffered a hemianopia