Scotoma

Scotoma

Infobox_Disease
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DiseasesDB =
ICD10 = ICD10|H|53|4|h|53, ICD10|H|53|1|h|53
ICD9 = ICD9|368.4, ICD9|368.12
ICDO =
OMIM =
MedlinePlus =
eMedicineSubj =
eMedicineTopic =
MeshID = 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.

Every normal 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 axons that comprise the optic nerve exit the retina. This location is called the optic disc. The blindspot does not intrude into consciousness because the corresponding visual field locations 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 fixation with the open eye, and placing an object (such as your thumb) in the lateral and horizontal visual field, about 15 degrees from fixation (see the blind spot article). The size of the monocular scotoma is surprisingly large - 5x7 degrees of visual angle.

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 because of the normal reduced Optical 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. ["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 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-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 preeclampsia, a form of pregnancy-induced hypertension. Similarly, scotomata may develop as a result of the increased intracranial pressure that occurs in malignant hypertension.

ee also

Detection

*Amsler grid
*Perimetry
*Visual field test

Types

*Binasal hemianopsia
*Bitemporal hemianopsia
*Blind spot
*Scintillating scotoma
*Cortical spreading depression

References


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Look at other dictionaries:

  • scotoma — (pl. scotomata), 1540s, from L.L. scotoma, from Gk. skotoma “dizziness,” from skotoun “to darken,” from skotos “darkness” (see SHADE (Cf. shade)) …   Etymology dictionary

  • Scotoma — Sco*to ma, n. [L.] (Med.) Scotomy. [1913 Webster] …   The Collaborative International Dictionary of English

  • scotoma — [skə tō′mə] n. pl. scotomata [skə tō′mə tə] or scotomas [ModL < LL, dimness of vision < Gr skotōma < skotos, darkness (see SHADE) + OMA] a dark area or gap in the visual field scotomatous [skətäm′ə təs] adj …   English World dictionary

  • scotoma —    Also known as negative scotoma. The term scotoma comes from the Greek noun skotos (darkness). It is used to denote an area or island of loss or impairment of vision, surrounded by a field of normal or relatively well preserved vision. In… …   Dictionary of Hallucinations

  • scotoma — 1. An isolated area of varying size and shape, within the visual field, in which vision is absent or depressed. 2. A blind spot in psychological awareness. [G. skotoma, vertigo, fr. skotos, darkness] absolute s. a s. in which there is no… …   Medical dictionary

  • scotoma — sco·tò·ma s.m. TS med. riduzione circoscritta della sensibilità luminosa nel campo visivo, dovuta a una lesione di un punto qualunque delle vie ottiche, dalla retina all area visiva corticale {{line}} {{/line}} DATA: av. 1749. ETIMO: dal gr.… …   Dizionario italiano

  • scotoma — n.; pl. scotomata a small area of abnormally less sensitive or absent vision in the visual field, surrounded by normal sight. All people have a blind spot in the visual field of each eye due to the small area inside the eye occupied by the optic… …   The new mediacal dictionary

  • scotoma — noun (plural mas or scotomata) Etymology: New Latin, from Medieval Latin, dimness of vision, from Greek skotōmat , skotōma, from skotoun to darken, from skotos Date: 1875 a spot in the visual field in which vision is absent or deficient …   New Collegiate Dictionary

  • Scotoma — Klassifikation nach ICD 10 H53.4 Gesichtsfelddefekte H53.1 Subjektive Sehstörungen Flimmerskotom …   Deutsch Wikipedia

  • scotoma — scotomatous /skoh tom euh teuhs/, adj. /skoh toh meuh/, n., pl. scotomas, scotomata / meuh teuh/. Pathol. loss of vision in a part of the visual field; blind spot. [1535 45; < LL < Gk skótoma dizziness. See SCOTO , OMA] * * * …   Universalium

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