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scotoma

  (skə-tō') pronunciation
n., pl. -mas or -ma·ta (-mə-tə).

An area of diminished vision within the visual field.

[New Latin scotōma, from Late Latin, dim sight, from Greek skotōma, dizziness, from skotoun, to darken, from skotos, darkness.]

scotomatous sco·to'ma·tous adj.
 
 
Medical Dictionary: sco·to·ma
(skə-tō')
n., pl. -mas or sco·to·ma·ta (-mə-tə).
  1. An area of diminished vision within the visual field.
  2. See blind spot (sense ).
 
Obscure Words: scotoma


[fr. Gk skotoma, dimness of vision < skotos, darkness]  /skuh TOE muh/  
Path.  an obscuration of part of the visual field (also fig.)
 
Wikipedia: scotoma
Scotoma
Classification & external resources
ICD-10 H53.4, H53.1
ICD-9 368.4, 368.12
MeSH D012607

A scotoma (Greek: darkness; plural: "scotomas" or "scotomata") is an area or island of loss or impairment of visual acuity surrounded by a field of normal or relatively well-preserved vision.

Example image showing normal field of vision.
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Example image showing normal field of vision.
Example image showing small, deep central scotoma, as may be caused by age-related maculopathy.
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Example image showing small, deep central scotoma, as may be caused by age-related maculopathy.
Example image showing a peripheral ring scotoma, as may be caused by retinitis pigmentosa.
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Example image showing a peripheral ring scotoma, as may be caused by retinitis pigmentosa.
Example of a scintillating scotoma, as may be caused by cortical spreading depression.
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Example of a scintillating scotoma, as may be caused by cortical spreading depression.

Every normal mammalian eye has a scotoma in its field of vision, usually termed its blind spot. The presence of this normal scotoma does not intrude into consciousness because it is very small, but it can be demonstrated to oneself by the simplest of clinical methods (such as the one in the blind spot article).

Presentation

Symptom-producing or pathological scotomata may be due to a wide range of disease processes, affecting either the retina (in particular its most sensitive portion, the macula) or the optic nerve itself. A pathological scotoma may involve any part of the visual field and may be of any shape or size. A scotoma may include and enlarge the normal blind spot. Even a small scotoma that happens to affect central or macular vision will produce a severe visual handicap, whereas a large scotoma in the more peripheral part of a visual field may go unnoticed by the bearer due to the normal reduced visual resolution in the peripheral visual field.

Causes

Common causes of scotomata include demyelinating disease such as multiple sclerosis (retrobulbar neuritis), toxic substances such as methyl alcohol, ethambutol and quinine, nutritional deficiencies, and vascular blockages either in the retina or in the optic nerve. Scintillating scotoma is a common visual aura in migraine.[1] Less common, but important because sometimes reversible or curable by surgery, are scotomata due to tumors such as those arising from the pituitary gland, which may compress the optic nerve or interfere with its blood supply.

Rarely, scotomata are bilateral. One important variety of bilateral scotoma may occur when a pituitary tumour begins to compress the optic chiasm (as distinct from a single optic nerve) and produces a bi-temporal hemicentral scotomatous hemianopia. This type of visual field defect tends to be very eloquent symptom-wise but often evades early objective diagnosis, as it is more difficult to detect by cursory clinical examination than the classical or text-book bi-temporal peripheral hemianopia and may even elude sophisticated electronic modes of visual field assessment.

See also

Detection

Types

References

  1. ^ "Possible Roles of Vertebrate Neuroglia in Potassium Dynamics, Spreading depression, and migraine", Gardner-Medwin, J. Exp. Biology (1981), 95, pages 111-127 (Figure 4).



 
 

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Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Medical Dictionary. The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company Read more
Obscure Words. © 2008 by Michael A. Fischer http://home.comcast.net/~wwftd Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Scotoma" Read more

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