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 brand names such as Henson 9000 Perimeter, Humphrey Field Analyzer, Octopus Perimeter, Oculus Easyfield perimeter, Olleyes VisuALL, Optopol PTS perimeter, etc. Examination methods Techniques used to perform this test include the confrontation visual field examination (Donders' test). The examiner will ask the patient to cover one eye and stare at the examiner. Ideally, when the patient covers their right eye, the examiner covers their left eye and vice versa. The examiner will then move his hand out of the patient's visual field and then bring it back in. Commonly the examiner will use a slowly wagging finger or a hat pin for this. The patient signals the examiner when his hand comes back into view. This is frequently done by an examiner as a simple and preliminary test. Perimetry 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 Tangent screen The simplest form of perimetry uses a white tangent screen. Vision is tested by presenting different sized pins attached to