Scotoma

A scotoma is an area of partial or complete blindness within an otherwise normal or slightly impaired visual field. Usually located within the central 30-degree area, the defect ranges from absolute blindness to a barely detectable loss of visual acuity. Typically, the patient can pinpoint the scotoma’s location in the visual field. (See Locating scotomas, page 550.)  

A scotoma can result from a retinal, choroid, or optic nerve disorder. It can be classified as absolute, relative, or scintillating. An absolute scotoma refers to the total inability to see all sizes of test objects used in mapping the visual field. A relative scotoma, in contrast, refers to the ability to see only large test objects. A scintillating scotoma refers to the flashes or bursts of light commonly seen during a migraine headache.

History and physical examination

First, identify and characterize the scotoma, using such visual field tests as the tangent screen examination, the Goldmann perimeter test, and the automated perimetry test. Two other visual field tests  —  confrontation testing and the Amsler grid   —  may also help in identifying a scotoma.

Next, test the patient’s visual acuity and inspect his pupils for size, equality, and reaction to light. An ophthalmoscopic examination and measurement of intraocular pressure are necessary.

Explore the patient’s medical history, noting especially eye disorders, vision problems, or chronic systemic disorders. Find out if he takes medications or uses eyedrops.

Medical causes

Chorioretinitis

Inflammation of the choroid and retina produces a paracentral scotoma. Ophthalmoscopic examination reveals clouding and cells in the vitreous, subretinal hemorrhage, and neovascularization. The patient may have photophobia along with blurred vision.

Macular degeneration

Any degenerative process or disorder affecting the fovea centralis results in a central scotoma. Ophthalmoscopic examination reveals changes in the macular area. The patient may notice subtle changes in visual acuity, in color perception, and in the size and shape of objects.

Optic neuritis

Inflammation, degeneration, or demyelination of the optic nerve produces a central, circular, or centrocecal scotoma. The scotoma may be unilateral with involvement of one nerve, or bilateral with involvement of both nerves. It can vary in size, density, and symmetry. The patient may report severe vision loss or blurring, lasting up to 3 weeks, and pain — especially with eye movement. Common ophthalmoscopic findings include hyperemia of the optic disk, retinal vein distention, blurred disk margins, and filling of the physiologic cup.

Retinal pigmentary degeneration

Retinal pigmentary degeneration causes premature retinal cell changes leading to cell death. One disorder, retinitis pigmentosa, initially involves loss of peripheral rods; the resulting annular scotoma progresses concentrically until only a central field of vision (tunnel vision) remains. The earliest symptom —  impaired night vision —  appears during adolescence. Associated signs include narrowing of the retinal blood vessels and pallor of the optic disk. Eventually, with invasion of the macula, blindness may occur.

Special considerations

For the patient with a disorder involving the fovea centralis (or the area surrounding it), teach him to periodically use the Amsler grid to detect progression of macular degeneration.

Pediatric pointers

In young children, visual field testing is difficult and requires patience. Confrontation testing is the method of choice.

Pictures

Book Source Details

• Book Title: Handbook of Signs & Symptoms (Third Edition)
• Author(s): Springhouse
• Year of Publication: 2006
• Copyright Details: Handbook of Signs & Symptoms (Third Edition), Copyright © 2006 Lippincott Williams & Wilkins.

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Copyright Details: Handbook of Signs & Symptoms (Third Edition), Copyright © 2008 Williams & Wilkins.

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More About This Book: Title: Handbook of Signs & Symptoms (Third Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2006 ISBN: 1-58255-402-1

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