The total area in which visual perception is possible while a person is looking straight ahead.
The visual fields normally extend outwards over an angle of about 90 degrees on either side of the midline of the face, but are more restricted above and below, especially if the eyes are deep-set or the eyebrows are prominent.
The visual fields of the 2 eyes overlap to a large extent, giving binocular vision.
Partial loss of the visual field may occur in glaucoma or stroke.
the area in front of the eye in any part of which an object can be seen without moving the eye. With both eyes open and looking straight forward it is possible to see well-illuminated objects placed anywhere in front of the eyes, although the eyebrows and eyelids reduce the extent of the field somewhat. This is the binocular visual field. With only one eye open the field is uniocular and is restricted inwards by the nose. If the object is small or poorly illuminated it will not be seen until it is moved closer to the point at which the eye is actually looking, i.e. nearer to the centre of the visual field. Similarly, coloured objects are not seen so far away from the centre as are white objects of the same size and brightness. This is because the retina is not uniformly sensitive to light of different colours or intensities (see rod; cone): retinal sensitivity increases towards its centre (the *macula). Thus, while there is an absolute visual field beyond which things cannot be seen, no matter how large or bright they are, a relative field exists for objects of different brightness, size, and colour. The most common visual field loss is due to *glaucoma. See also perimeter.
Stimulation of the retina of the EYE with light causes changes in the electrical activity of the cerebral cortex (see BRAIN). These changes can be measured from outside the skull and can give valuable information about the state of the visual pathway from the retinal ganglion cells to the occipital cortex. Not only can it determine that function is normal, it can also help to diagnose some causes of poor VISION.... visual evoked response
n. (in radiotherapy) an area of the body selected for treatment with radiotherapy. For example, a mantle field comprises the neck, armpits, and central chest, for the radiotherapy of Hodgkin’s disease. Radiation is administered to the defined area by focusing the beam of particles emitted by the radiotherapy machine and shielding the surrounding area of the body.... treatment field
(visual reinforced audiometry, VRA) a behavioural test of hearing for children aged approximately 6 to 30 months in which the subject sits between two calibrated loudspeakers. A sound is generated from one loudspeaker. Children who turn towards the sound are rewarded by brief illumination of a toy adjacent to the loudspeaker. Older children can be tested with headphones, rather than using the loudspeakers, to enable each ear to be tested separately. The test can be adapted for use with older subjects who have learning disabilities.... visual reinforcement audiometry
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