Visual field defect

The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments".

The equivalent concept for optical instruments and sensors is the field of view (FOV).

In optometry, ophthalmology, and neurology, 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 (increase in threshold).

The normal (monocular) human visual field extends to approximately 60 degrees nasally (toward the nose, or inward) from the vertical meridian in each eye, to 107 degrees temporally (away from the nose, or outwards) from the vertical meridian, and approximately 70 degrees above and 80 below the horizontal meridian.

The binocular visual field is the superimposition of the two monocular fields. In the binocular field, the area left of the vertical meridian is referred to as the left visual field (which is temporally for the left, and nasally for the right eye); a corresponding definition holds for the right visual field. The four areas delimited by the vertical and horizontal meridian are referred to as upper/lower left/right quadrants. 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 17 degrees diameter of the visual field; the fovea to the central 5.2 degrees, and the foveola to 1–1.2 degrees diameter.

The visual field is measured by perimetry. This may be kinetic, where spots of light are shown on the white interior of a half sphere and slowly moved inwards until the observer sees them, or static, where the light spots are flashed at varying intensities at fixed locations in the sphere until detected by the subject. Commonly used perimeters are the automated Humphrey Field Analyzer, the Heidelberg Edge Perimeter, or the Oculus.

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

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