|ICD-9-CM 95.05||MeSH D010499|
A visual field test is an eye examination that can detect dysfunction in central and peripheral vision which may be caused by various medical conditions such as glaucoma, stroke, pituitary disease, brain tumours or other neurological deficits. Visual field testing can be performed clinically by keeping the subject's gaze fixed while presenting objects at various places within their visual field. Simple manual equipment can be used such as in the tangent screen test or the Amsler grid. When dedicated machinery is used it is called a perimeter.
The exam may be performed by a technician in one of several ways. The test may be performed by a technician directly, with the assistance of a machine, or completely by an automated machine. Machine based tests aid diagnostics by allowing a detailed printout of the patient's visual field.
Other names for this test may include perimetry, Tangent screen exam, Automated perimetry exam, Goldmann visual field exam, or the Humphrey field exam.
Techniques used to perform this test:
Perimetry or campimetry is one way to systematically test the visual field. It is the systematic measurement of differential light sensitivity in the visual field by the detection of the presence of test targets on a defined background. Perimetry more carefully maps and quantifies the visual field, especially at the extreme periphery of the visual field. The name comes from the method of testing the perimeter of the visual field.
Automated perimeters are used widely, and applications include: diagnosing disease, job selection, visual competence assessment, school or community screenings, military selection, and disability classifications.
Types of perimetry
Static perimetry tests different locations throughout the field one at a time. First, a dim light is presented at a particular location. If the patient does not see the light, it is made gradually brighter until it is seen. The minimum brightness required for the detection of a light stimulus is called the "threshold" sensitivity level of that location. This procedure is then repeated at several other locations, until the entire visual field is tested.
Threshold static perimetry is generally done using automated equipment. It is used for rapid screening and follow up of diseases involving deficits such as scotomas, loss of peripheral vision and more subtle vision loss. Perimetry testing is important in the screening, diagnosing, and monitoring of various eye, retinal, optic nerve and brain disorders.
Kinetic perimetry uses a mobile stimulus moved by an examiner (perimetrist) such as in Goldmann kinetic perimetry. First, a single test light of constant size and brightness is used. The test light is moved towards the center of vision from the periphery until it is first detected by the patient. This repeated by approaching the center of vision from different directions. Repeating this enough will establish a boundary of vision for that target. The procedure is repeated using different test lights that are larger or brighter than the original test light.
In this way, kinetic perimetry is useful for mapping visual field sensitivity boundaries. It may be a good alternative for patients that have difficulty with automated perimetry, either due to difficulty maintaining constant gaze, or due to cognitive impairment.