Scotoma: Difference between revisions
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[[File:Scintillating scotoma.gif|thumb|right|235px|A depiction of a [[scintillating scotoma]] that was almost spiral-shaped, with distortion of shapes but otherwise melting into the background similarly to the [[blind spot (vision)|physiological blind spot]], as may be caused by [[cortical spreading depression]]]] |
[[File:Scintillating scotoma.gif|thumb|right|235px|A depiction of a [[scintillating scotoma]] that was almost spiral-shaped, with distortion of shapes but otherwise melting into the background similarly to the [[blind spot (vision)|physiological blind spot]], as may be caused by [[cortical spreading depression]]]] |
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Every normal [[mammal]]ian eye has a scotoma in its field of vision, usually termed its [[blind spot (vision)|blind spot]]. This is a location with no [[photoreceptor cell]]s, where the [[retina]]l [[ganglion cell]] [[axons]] that compose the [[optic nerve]] exit the retina. This location is called the [[optic disc]]. |
Every normal [[mammal]]ian eye has a scotoma in its field of vision, usually termed its [[blind spot (vision)|blind spot]]. This is a location with no [[photoreceptor cell]]s, where the [[retina]]l [[ganglion cell]] [[axons]] that compose the [[optic nerve]] exit the retina. This location is called the [[optic disc]]. There is no direct conscious awareness of visual scotomas. They are simply regions of reduced information within the the visual field. Rather than recognizing an incomplete image, patients with scotomas report that thing "disappear" on them<ref>"Patient awareness of binocular central scotoma in age-related macular degeneration.", Fletcher DC1, Schuchard RA, Renninger LW., ''Optom Vis Sci'' (2012), 89(9), pages 1395-8.</ref>. |
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The presence of the scotoma can be demonstrated subjectively by covering one eye, carefully holding [[Fixation (visual)|fixation]] with the open eye, and placing an object (such as one's thumb) in the [[Human anatomical terms#Anatomical directions|lateral]] and [[Horizontal plane|horizontal]] visual field, about 15 degrees from fixation (see the [[blind spot (vision)|blind spot]] article). The size of the [[monocular]] scotoma is 5×7 degrees of [[visual angle]]. |
The presence of the scotoma can be demonstrated subjectively by covering one eye, carefully holding [[Fixation (visual)|fixation]] with the open eye, and placing an object (such as one's thumb) in the [[Human anatomical terms#Anatomical directions|lateral]] and [[Horizontal plane|horizontal]] visual field, about 15 degrees from fixation (see the [[blind spot (vision)|blind spot]] article). The size of the [[monocular]] scotoma is 5×7 degrees of [[visual angle]]. |
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Scotoma is |
Scotoma is a symptom of damage to any part of the visual system, such as retinal damage from exposure to high-powered lasers, [[macular degeneration]] and brain damage. |
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The term ''scotoma'' is also used [[metaphor]]ically in [[psychology]] to refer to an individual's inability to perceive [[personality trait]]s in themselves that are obvious to others. |
The term ''scotoma'' is also used [[metaphor]]ically in [[psychology]] to refer to an individual's inability to perceive [[personality trait]]s in themselves that are obvious to others. |
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==Presentation of pathological scotoma== |
==Presentation of pathological scotoma== |
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Symptom-producing, or [[pathology|pathological]], scotomata may be due to a wide range of disease processes, affecting |
Symptom-producing, or [[pathology|pathological]], scotomata may be due to a wide range of disease processes, affecting any part of the visual system, including the [[retina]] (in particular its most sensitive portion, the [[macula]]), the [[optic nerve]] and even the visual cortex<ref>"Bilateral effects of unilateral visual cortex lesions in human", Matthew Rizzo and Donald A. Robin, ''Brain'' (1996), 119, pages 951-96.</ref>.{{Contradict-inline|article=Visual_cortex#Current_research|date=October 2013}} 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 [[macula]]r vision will produce a severe visual [[disability|handicap]], whereas a large scotoma in the more [[Peripheral vision|peripheral]] part of a visual field may go unnoticed by the bearer because of the normal reduced [[optical resolution]] in the peripheral visual field. |
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==Causes== |
==Causes== |
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Common causes of scotomata include [[demyelinating]] disease such as [[multiple sclerosis]] ([[retrobulbar neuritis]]), damage to nerve fiber layer in the retina (seen as cotton wool spots) due to hypertension, toxic substances such as [[methyl alcohol]], [[ethambutol]] and [[quinine]], [[nutritional deficiencies]], |
Common causes of scotomata include [[demyelinating]] disease such as [[multiple sclerosis]] ([[retrobulbar neuritis]]), damage to nerve fiber layer in the retina (seen as cotton wool spots<ref>"The role of axoplasmic transport in the pathogenesis of retinal cotton-wool spots", D. McLeod, J. Marshall, E. M. Kohner, and A. C. Bird, ''Br J Ophthalmol'' (1977), 61(3), pages 177–191.</ref>) due to hypertension, toxic substances such as [[methyl alcohol]], [[ethambutol]] and [[quinine]], [[nutritional deficiencies]], [[blood vessel|vascular]] blockages either in the retina or in the optic nerve and [[macular degeneration]], often associated with aging. [[Scintillating scotoma]] is a common visual [[Aura (symptom)|aura]] in [[migraine]].<ref>"Possible Roles of Vertebrate Neuroglia in Potassium Dynamics, Spreading depression, and migraine", Gardner-Medwin, ''J. Exp. Biology'' (1981), 95, pages 111-127 (Figure 4).</ref> Less common, but important because they are sometimes reversible or curable by [[surgery]], are scotomata due to [[tumor]]s such as those arising from the [[pituitary gland]], which may compress the optic nerve or interfere with its blood supply. |
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Rarely, scotomata are [[wikt:bilateral|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 [[paracentral scotoma|bitemporal paracentral scotoma]], and later, when the tumor enlarges, the scotomas extend out to the periphery to cause the characteristic [[bitemporal hemianopsia]]. This type of visual-field defect tends to be obvious to the person experiencing it but often evades early objective [[medical diagnosis|diagnosis]], as it is more difficult to detect by cursory clinical examination than the classical or textbook bitemporal peripheral hemianopia and may even elude sophisticated electronic modes of visual-field assessment. |
Rarely, scotomata are [[wikt:bilateral|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 [[paracentral scotoma|bitemporal paracentral scotoma]], and later, when the tumor enlarges, the scotomas extend out to the periphery to cause the characteristic [[bitemporal hemianopsia]]. This type of visual-field defect tends to be obvious to the person experiencing it but often evades early objective [[medical diagnosis|diagnosis]], as it is more difficult to detect by cursory clinical examination than the classical or textbook bitemporal peripheral hemianopia and may even elude sophisticated electronic modes of visual-field assessment. |
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Revision as of 04:43, 24 April 2014
| Scotoma | |
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| Specialty | Ophthalmology  |
A scotoma (Greek σκότος/skótos, darkness; plural: scotomas or scotomata) is an area of partial alteration in the field of vision consisting of a partially diminished or entirely degenerated visual acuity that 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 termed its blind spot. This is a location with no photoreceptor cells, where the retinal ganglion cell axons that compose the optic nerve exit the retina. This location is called the optic disc. There is no direct conscious awareness of visual scotomas. They are simply regions of reduced information within the the visual field. Rather than recognizing an incomplete image, patients with scotomas report that thing "disappear" on them[1].
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 one's 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 5×7 degrees of visual angle.
Scotoma is a symptom of damage to any part of the visual system, such as retinal damage from exposure to high-powered lasers, macular degeneration and brain damage.
The term scotoma is also used metaphorically in psychology to refer to an individual's inability to perceive personality traits in themselves that are obvious to others.
Presentation of pathological scotoma
Symptom-producing, or pathological, scotomata may be due to a wide range of disease processes, affecting any part of the visual system, including the retina (in particular its most sensitive portion, the macula), the optic nerve and even the visual cortex[2].[[[Visual_cortex#Current_research#{{{section}}}|contradictory]]] 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), damage to nerve fiber layer in the retina (seen as cotton wool spots[3]) due to hypertension, toxic substances such as methyl alcohol, ethambutol and quinine, nutritional deficiencies, vascular blockages either in the retina or in the optic nerve and macular degeneration, often associated with aging. Scintillating scotoma is a common visual aura in migraine.[4] Less common, but important because they are 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 bitemporal paracentral scotoma, and later, when the tumor enlarges, the scotomas extend out to the periphery to cause the characteristic bitemporal hemianopsia. This type of visual-field defect tends to be obvious to the person experiencing it but often evades early objective diagnosis, as it is more difficult to detect by cursory clinical examination than the classical or textbook bitemporal 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.
See also
Detection
Types
- Binasal hemianopsia
- Bitemporal hemianopsia
- Blind spot
- Cortical spreading depression
- Scintillating scotoma
References
- ^ "Patient awareness of binocular central scotoma in age-related macular degeneration.", Fletcher DC1, Schuchard RA, Renninger LW., Optom Vis Sci (2012), 89(9), pages 1395-8.
- ^ "Bilateral effects of unilateral visual cortex lesions in human", Matthew Rizzo and Donald A. Robin, Brain (1996), 119, pages 951-96.
- ^ "The role of axoplasmic transport in the pathogenesis of retinal cotton-wool spots", D. McLeod, J. Marshall, E. M. Kohner, and A. C. Bird, Br J Ophthalmol (1977), 61(3), pages 177–191.
- ^ "Possible Roles of Vertebrate Neuroglia in Potassium Dynamics, Spreading depression, and migraine", Gardner-Medwin, J. Exp. Biology (1981), 95, pages 111-127 (Figure 4).