The term
visual field is sometimes used as a
synonymSynonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...
to
field of viewThe field of view is the extent of the observable world that is seen at any given moment....
, though they do not designate the same thing. The visual field is the "
spatial array of visual sensations available to observation in introspectionIntrospection is the self-observation and reporting of conscious inner thoughts, desires and sensations. It is a conscious and purposive process relying on thinking, reasoning, and examining one's own thoughts, feelings, and, in more spiritual cases, one's soul...
ist psychological experiments", while 'field of view' "
refers to the physical objects and light sources in the external world that impinge the retinaThe vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
". 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 systemThe visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
, which computes the visual field as the output.
The term
visual field is sometimes used as a
synonymSynonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...
to
field of viewThe field of view is the extent of the observable world that is seen at any given moment....
, though they do not designate the same thing. The visual field is the "
spatial array of visual sensations available to observation in introspectionIntrospection is the self-observation and reporting of conscious inner thoughts, desires and sensations. It is a conscious and purposive process relying on thinking, reasoning, and examining one's own thoughts, feelings, and, in more spiritual cases, one's soul...
ist psychological experiments", while 'field of view' "
refers to the physical objects and light sources in the external world that impinge the retinaThe vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
". 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 systemThe visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
, which computes the visual field as the output.
The term is often used in
optometryOptometry is a health care profession concerned with eyes and related structures, as well as vision, visual systems, and vision information processing in humans. Optometrists, or Doctors of Optometry, are state licensed medical professionals trained to prescribe and fit lenses to improve vision,...
and
ophthalmologyOphthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
, where a
visual field testA 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...
is used to determine whether the visual field is affected by diseases that cause local
scotomaA scotoma is an area of partial alteration in one's field of vision consisting of a partially diminished or entirely degenerated visual acuity which is surrounded by a field of normal - or relatively well-preserved - vision.Every normal mammalian eye has a scotoma in its field of vision, usually...
or a more extensive loss of vision or a reduction in sensitivity (threshold).
Normal limits
The normal human visual field extends to approximately 60 degrees nasally (toward the nose, or inward) from the vertical meridian in each eye, to 100 degrees temporally (away from the nose, or outwards) from the vertical meridian, and approximately 60 degrees above and 75 below the horizontal meridian. In the
United KingdomThe United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, the minimum field requirement for driving is 60 degrees either side of the vertical meridian, and 20 degrees above and below horizontal. The
maculaThe macula or macula lutea is an oval-shaped highly pigmented yellow spot near the center of the retina of the human eye. It has a diameter of around 5 mm and is often histologically defined as having two or more layers of ganglion cells...
corresponds to the central 13 degrees of the visual field; the
foveaThe fovea centralis, also generally known as the fovea , is a part of the eye, located in the center of the macula region of the retina....
to the central 3 degrees.
Measuring the visual field
The visual field is measured by
perimetryPerimetry or campimetry is the systematic measurement of differential light sensitivity in the visual field by the detection of the presence of test targets on a defined background. Visual field testing can be performed clinically with confrontational field testing keeping the subject's gaze fixed...
. 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
campimeterThe campimeter is an instrument for examining the visual field. Campimeters have been in clinical use since the mid-nineteenth century. Initially, examination of the visual field was concerned only with the outer limits, or 'perimeter' of the visual field, hence the term 'perimetry', which tends to...
, 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.
Visual field loss
Visual field loss may occur due to disease or disorders of the
eyeThe human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
,
optic nerveThe optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...
, or
brainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
.
Classically, there are four types of visual field defects:
- Altitudinal field defects, loss of vision above or below the horizontal – associated with ocular abnormalities
- Bitemporal hemianopia, loss of vision at the sides (see below)
- Central scotoma, loss of central vision
- Homonymous hemianopia, loss at one side in both eyes – defect behind optic chiasm
The optic chiasm or optic chiasma is the part of the brain where the optic nerves partially cross...
(see below)
In humans, confrontational testing and other forms of
perimetryPerimetry or campimetry is the systematic measurement of differential light sensitivity in the visual field by the detection of the presence of test targets on a defined background. Visual field testing can be performed clinically with confrontational field testing keeping the subject's gaze fixed...
are used to detect and measure visual field loss. Different neurological difficulties cause characteristic forms of visual disturbances, including
hemianopsiaHemianopia, or hemianopsia, is a type of anopsia where the decreased vision or blindness takes place in half the visual field of one or both eyes. In most cases, the visual field loss respects the vertical midline...
s (shown below
without macular sparing), quadrantanopsia, and others.
External links