Visual field
The spatial array of visible objects during steady gaze fixation.
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The visual field is the portion of space in which objects are visible during steady fixation of the gaze in one direction. In ophthalmology and neurology, it is considered the field of functional capacity obtained and recorded by perimetry. It can also be understood as a perceptual concept, referring to the spatial array of visual sensations available to observation in introspectionist psychological experiments.
Quick Facts
- Field
- Ophthalmology
- neurology
- psychology
- Known for
- Spatial array of visual sensations; functional capacity measured by perimetry
Facts from the source article.
Normal limits
The binocular visual field results from superimposing the two monocular fields. The left visual field lies left of the vertical meridian, and the right visual field lies right of it. The four quadrants are upper/lower left and right. In the European Union, the minimum driving requirement is 50 degrees to each side of the vertical meridian, 120 degrees total horizontally, and 20 degrees above and below the horizontal meridian.
The macula covers the central 17 degrees diameter, the fovea 5.2 degrees, and the foveola 1–1.2 degrees. In clinical literature, the fovea may refer to the central 1–1.2 degrees, also called the clinical fovea. The nose is in the field of view but is not noticed during normal visual tasks.
Measuring the visual field
The visual field is measured by perimetry, which may be kinetic (moving light spots inward until seen) or static (flashing spots at fixed locations at varying intensities). Common perimeters include the Humphrey Field Analyzer, Optopol Perimeters, Octopus, Heidelberg Edge Perimeter, Oculus, and Olleyes VisuALL. A campimeter, a flat-screen device, measures the central visual field.
Patterns testing the central 24 or 30 degrees are most common; most perimeters can test up to 80, 90, or 120 degrees. Confrontational field testing involves the practitioner holding up fingers in the four quadrants and center of the patient's visual field; a normal result is recorded as full to finger counting (FTFC). The blind spot can be assessed by comparing when a small object disappears for the practitioner and patient.
Visual field loss
Visual field loss can result from diseases or disorders of the eye, optic nerve, or brain. Glaucoma causes peripheral field defects; macular degeneration and other macular diseases cause central defects. Lesions of the visual pathway produce characteristic disturbances such as homonymous hemianopsia, quadrantanopsia, and scotomata. Defects are classified by location: retinal lesions (heteronymous defects in glaucoma and AMD), optic nerve lesions (heteronymous defects), chiasmal lesions (e.g., bitemporal hemianopia), and post-chiasmal lesions (homonymous defects like homonymous hemianopia, quadrantanopia, homonymous scotomata).
Other characterizations include altitudinal field defects, central scotoma, peripheral field loss including tunnel vision, and generalized depression. In glaucoma, damage to the retinal nerve fiber layer causes field defects, mainly in primary open angle glaucoma. Early changes appear in Bjerrum's area, 10°–20° from fixation. Common glaucomatous defects include generalized depression (also seen in cataract), relative paracentral scotomas, small paracentral depressions (superonasal in normal-tension glaucoma), and baring of the blind spot, which is an early non-specific change.
More in Sensory Systems
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Visual field (CC BY-SA 4.0).
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