Visual field test

A visual field test is an examination that may be performed to analyze a patient's visual field. 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 Humphrey field exam.

Exam Methods

Here is a list of techniques used to perform this test:

• Confrontation visual field exam - The examiner will ask the patient to cover one eye and stare at the examiner. The examiner will then move her hand out of the patient's visual field and then bring it back in. The patient signals the examiner when her hand comes back into view. This is frequently done by an examiner as a simple and preliminary test.
• Tangent screen exam or Goldmann field exam - Here the patient is asked to sit approximately 3 feet from a screen with a target on the center. The eye that isn't tested is covered during the exam. While the patient stares at the target the examiner will move an object toward the patient's visual field. The patient signals the examiner when the object comes into view. This exam allows the patient's visual field to be mapped.
• Automated perimetry exam - The patient sits in front of a concave dome with a target in the center. The eye that is not being tested is covered. A button is given to the patient to be used during the exam. The patient is set in front of the dome and asked to focus on the target at the center. A computer then shines lights on the inside dome and the patient clicks the button whenever a light is seen. The computer then automatically maps and calculates the patient's visual field. (See Perimetry for details.)

Reference: Siverstone, DE, Hirsch, J: Automated Visual Field Testing. Appelton-Century Croft. Norwalk, CT. 1986.

Self Examination

Various methods of self examination are available in situations where professional testing is not available. Online self examination is possible at www.testvision.org.

External links

• IXMUS Color Field Test for Macula and Optic nerve Disease
• MedicinePlus Medical Encyclopedia: Visual Field

Bold text==References==

Visual field From Wikipedia, the free encyclopediaJump to: navigation, search The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments"[1], while 'field of view' "refers to the physical objects and light sources in the external world that impinge the retina". In other words, field of view is everything that (at a given time) causes light to fall onto the retina. This input is processed by the visual system, which computes the visual field as the output.

The term is often used in optometry and ophthalmology, where a visual field test is used to determine whether the visual field is affected by diseases that cause local scotoma or a more extensive loss of vision or a reduction in sensitivity (threshold).

Contents [hide] 1 Normal limits 2 Measuring the visual field 3 Visual field loss 4 References 5 External links

[edit] Normal limits The normal human visual field extends to approximately 60 degrees nasally (toward the nose, or inward) in each eye, to 100 degrees temporally (away from the nose, or outwards), and approximately 60 degrees above and 75 below the horizontal meridian.[citation needed] In the United Kingdom, the minimum field requirement for driving is 60 degrees either side of the vertical meridian, and 20 degrees above and below horizontal. The macula corresponds to the central 13 degrees of the visual field; the fovea to the central 3 degrees.

[edit] Measuring the visual field The visual field is measured by perimetry. This may be kinetic, where points of light are moved inwards until the observer sees them, or static, where points of light are flashed onto a white screen and the observer is asked to press a button if he or she sees it. The most common perimeter used is the automated Humphrey Field Analyzer.

Another method is to use a campimeter, a small device designed to measure the visual field.

Patterns testing the central 24 degrees or 30 degrees of the visual field, are most commonly used. Most perimeters are also capable of testing the full field of vision.

[edit] Visual field loss Visual field loss may occur due to disease or disorders of the eye, optic nerve, or brain. Classically, there are four types of visual field defects:[2]

1.Altitudinal field defects, loss of vision above or below the horizontal – associated with ocular abnormalities 2.Bitemporal hemianopia, loss of vision at the sides (see below) 3.Central scotoma, loss of central vision 4.Homonymous hemianopia, loss at one side in both eyes – defect behind optic chiasm (see below) In humans, confrontational testing and other forms of perimetry are used to detect and measure visual field loss. Different neurological difficulties cause characteristic forms of visual disturbances, including hemianopsias (shown below without macular sparing), quadrantanopsia, and others.

Paris as seen with full visual fields

Paris as seen with bitemporal hemianopsia

Paris as seen with binasal hemianopsia

Paris as seen with left homonymous hemianopsia

Paris as seen with right homonymous hemianopsia

[edit] References 1.^ Smythies J (1996). "A note on the concept of the visual field in neurology, psychology, and visual neuroscience". Perception 25 (3): 369–71. doi:10.1068/p250369. PMID 8804101. 2.^ Jay WM (1981). "Visual field defects". American family physician 24 (2): 138–42. PMID 7258077. [edit] External links MedlinePlus Encyclopedia Visual Field Diagram linking defects to damage, at Brown Patient Plus Quadrantanopsia Visual Fields Teaching Case from MedPix