The term visual field is sometimes used as a synonym Synonyms are different words with identical or very 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 ("with") and onoma (ὄνομα) ("name"). The words car and automobile are synonyms. Similarly, if we talk about a to field of view The field of view is the (angular or linear or areal) 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 introspectionist Introspection is the self-observation and reporting of conscious inner thoughts, desires and sensations. It is a conscious mental and usually purposive process relying on thinking, reasoning, and examining one's own thoughts, feelings, and, in more spiritual cases, one's soul. It can also be called contemplation of one's self, and is contrasted psychological experiments"[1], while 'field of view' "refers to the physical objects and light sources in the external world that impinge the retina The 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 events that ultimately trigger nerve impulses. These". 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 The 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. The visual system accomplishes a number of complex tasks, including the, which computes the visual field as the output.

The term is often used in optometry Optometry is a health care profession concerned with eyes and related structures, as well as vision, visual systems, and vision information processing in humans and ophthalmology Ophthalmology is the branch of medicine which deals with the anatomy, physiology and diseases of the eye. The term ophthalmologist refers to a specialist in medical and surgical eye problems. Since ophthalmologists perform operations on eyes, they are considered to be both surgical and medical specialists, where a visual field test A 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. Machine based tests aid diagnostics by allowing a detailed is used to determine whether the visual field is affected by diseases that cause local scotoma A scotoma is an area of partial alteration in one's field of vision consisting in a partially diminished or entirely degenerated visual acuity which is surrounded by a field of normal - or relatively well-preserved - vision or a more extensive loss of vision Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically (i.e. over a long period of time) or a reduction in sensitivity (threshold).

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Normal limits

The normal human visual field extends to approximately 60 degrees nasally (toward the nose, or inward) in each eye, to 100 degrees temporally (away from the nose, or outwards), and approximately 60 degrees above and 75 below the horizontal meridian.[citation needed] In the United Kingdom The United Kingdom of Great Britain and Northern Ireland[note 7] is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of the island of Ireland, and many small islands. Northern Ireland is the only part of the UK with a land, the minimum field requirement for driving is 60 degrees either side of the vertical meridian, and 20 degrees above and below horizontal. The macula The 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. Near its center is the fovea, a small pit that contains the largest concentration of cone cells in the eye and corresponds to the central 13 degrees of the visual field; the fovea The 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. The fovea is responsible for sharp central vision (also called foveal vision), which is necessary in humans for reading, watching television or movies, driving, and any activity where visual detail is of primary to the central 3 degrees.

Measuring the visual field

The visual field is measured by perimetry Perimetry 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 while presenting objects at various places in. 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 campimeter, 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 eye Eyes are organs that detect light, and convert it to electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement. In higher organisms complex neural pathways exist that connect the eye, via the optic nerve to the visual cortex and other areas of the brain. Complex optical systems with resolving, optic nerve The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during embryonic development. Consequently, the fibres are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system, or brain. Classically, there are four types of visual field defects:[2]

In humans, confrontational testing and other forms of perimetry Perimetry 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 while presenting objects at various places in 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 It can be associated with a lesion of an optic radiation. If Meyer's loop is lesioned, the vision loss is superior; if the parietal path is lesioned, the vision loss is inferior, and others.

Paris as seen with full visual fields
Paris as seen with bitemporal hemianopsia Bitemporal hemianopsia is the medical description of a type of partial blindness where vision is missing in the outer half of both the right and left visual field. It is usually associated with lesions of the optic chiasm, the area where the optic nerves from the right and left eyes cross near the pituitary gland
Paris as seen with binasal hemianopsia Binasal hemianopsia is the medical description of a type of partial blindness where vision is missing in the inner half of both the right and left visual field. It is associated with certain lesions of the eye and of the central nervous system, such as congenital hydrocephalus
Paris as seen with left homonymous hemianopsia Homonymous hemianopsia, or homonymous hemianopia, is a medical term for a type of partial blindness resulting in a loss of vision in the same visual field of both eyes
Paris as seen with right homonymous hemianopsia Homonymous hemianopsia, or homonymous hemianopia, is a medical term for a type of partial blindness resulting in a loss of vision in the same visual field of both eyes

References

  1. ^ Smythies J (1996). "A note on the concept of the visual field in neurology, psychology, and visual neuroscience". Perception 25 (3): 369–71. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1068/p250369. PMID A PMID is a unique number assigned to each PubMed citation of life sciences and biomedical scientific journal articles. The related Pubmed Central archive may additionally assign a separate number, a PMCID (PubMed Central Identifier), normally written with a PMC prefix 8804101.
  2. ^ Jay WM (1981). "Visual field defects". American family physician 24 (2): 138–42. PMID A PMID is a unique number assigned to each PubMed citation of life sciences and biomedical scientific journal articles. The related Pubmed Central archive may additionally assign a separate number, a PMCID (PubMed Central Identifier), normally written with a PMC prefix 7258077.

External links

Categories: Vision Categories: Optics | Senses | Light | Perception | Ophthalmology Categories: Medical specialties | Surgical specialties | Eye | Vision

 

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