Visual field

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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" (J. Smythies [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.

1 Normal limits
2 Measuring the visual field
3 Visual field loss
4 External links

[edit] Normal limits

The normal human visual field extends to approximately 35 degrees nasally (toward the nose, or inward) in each eye, to 90 degrees temporally (away from the nose, or outwards), and approximately 50 degrees above and below the horizontal meridian. 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 dynamic (eg. Goldmann), 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 commonest perimetry used is the automated Humphrey (static) perimeter. It usually tests either the central 24 degrees or 30 degrees of the visual field.

[edit] Visual field loss

Visual field loss may occur due to disease or disorders of the eye, optic nerve, or brain. 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.