Name = PAGENAME
ICD10 = ICD10|H|53|4|h|53, ICD10|H|53|1|h|53
ICD9 = ICD9|368.4, ICD9|368.12
MeshID = D012607
A scotoma (Greek: "darkness"; plural: "scotomas" or "scotomata") is an area or island of loss or impairment of
visual acuitysurrounded by a field of normal or relatively well-preserved vision.
mammalian eye has a scotoma in its field of vision, usually termed its blind spot. This is a location with no photoreceptors, where the retinal ganglion cell axonsthat comprise the optic nerveexit the retina. This location is called the optic disc. The blindspot does not intrude into consciousnessbecause the corresponding visual fieldlocations of the optic discs in the two eyes differ: The visual signals that are absent in one eye are sent to the cortex by signals from the other eye.
The term is also used
metaphorically in the field of psychology, in reference to an individual's inability to perceive personality traits in themselves that are obvious to others.
The presence of the scotoma can be demonstrated subjectively by covering one eye, carefully holding
fixationwith the open eye, and placing an object (such as your thumb) in the lateraland horizontalvisual field, about 15 degrees from fixation (see the blind spot article). The size of the monocularscotoma is surprisingly large - 5x7 degrees of visual angle.
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 nerveitself. A pathological scotoma may involve any part of the visual fieldand 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 because of the normal reduced Optical resolutionin the peripheral visual field.
Common causes of scotomata include
demyelinatingdisease such as multiple sclerosis( retrobulbar neuritis), toxic substances such as methyl alcohol, ethambutoland quinine, nutritional deficiencies, and vascular blockages either in the retina or in the optic nerve. Scintillating scotomais a common visual aura in migraine. ["Possible Roles of Vertebrate Neuroglia in Potassium Dynamics, Spreading depression, and migraine", Gardner-Medwin, "J. Exp. Biology" (1981), 95, pages 111-127 (Figure 4).] 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 tumourbegins 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-wiseclarifyme 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.
In a pregnant woman, scotomata can present as a symptom of severe pre
eclampsia, a form of pregnancy-induced hypertension. Similarly, scotomata may develop as a result of the increased intracranial pressurethat occurs in malignant hypertension.
Visual field test
Cortical spreading depression
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