Night blindness [Nyctalopia]
Night blindness [Nyctalopia]: Excerpt from Professional Guide to Signs & Symptoms (Fifth Edition)
Often difficult to identify, night blindness refers to impaired vision in the dark, especially after entering a darkened room or while driving at night. A symptom of choroidal and retinal degeneration, night blindness occurs in various ocular disorders and as an early indicator of vitamin A deficiency. In some patients, however, night blindness occurs without underlying pathology, simply reflecting poor adaptation to the dark. In these patients, it’s commonly accompanied by myopia.
History and physical examination
If the patient complains of difficulty seeing at night, ask when he first noticed the problem. Is it intermittent or steadily worsening? Is it worse at certain times or in certain conditions? Also, ask about other ocular symptoms, such as eye pain, blurred or halo vision, floaters or spots, and photophobia.
Explore any history of glaucoma, cataracts, and familial degeneration of vision. If no ocular problems are apparent, briefly evaluate the patient’s nutritional status for vitamin A deficiency.
Examine the eyes for ptosis, abnormal tearing, discharge, and conjunctival injection. Test visual acuity and visual fields in both eyes and, if trained and equipped, measure intraocular pressure. Check pupillary response, and evaluate extraocular muscle function by testing the six cardinal fields of gaze.
Medical causes
Cataracts
Night blindness and halo vision occur early in senile-type cataract formation. As the cataract matures, it causes gradual, painless visual blurring and vision loss, sometimes with visible lens opacity.
Choroidal dystrophies
Night blindness and decreased peripheral vision may occur early in choroidal dystrophies. Disease progression causes loss of central vision.
Fundus albipunctatus
Night blindness is the chief complaint in this retinal and choroidal disease. Multiple small, round, yellow-white dots are present on the retina.
Fundus flavimaculatus
With this disease, night blindness may be pronounced or may be an incidental finding. Irregular yellow or white lesions appear deep in the retina.
Glaucoma
Night blindness occurs late in chronic open-angle glaucoma, with halo vision, gradually impaired bilateral visual acuity, loss of peripheral vision and, possibly, slight eye pain.
Goldman-Favre dystrophy
With this disorder, night blindness is usually the chief complaint. The retina resembles that seen in retinitis pigmentosa.
Oguchi’s disease
This rare, hereditary retinal and choroidal degeneration produces night blindness and a retina with a yellowish metallic sheen.
Optic nerve atrophy
This disorder may cause night blindness, visual field and color vision defects, and decreased visual acuity. Pupillary reactions are sluggish, and optic disk pallor is evident.
Retinitis pigmentosa
In this usually hereditary retinal degeneration, night blindness is characteristically the first symptom, usually arising in adolescence. Scattered black pigmentary bodies form in a characteristic “bone-spicule” arrangement on the retina. As the disease progresses, the visual field gradually constricts, causing tunnel or “gun barrel” vision and eventually total blindness.
Vitamin A deficiency
Night blindness is typically the first symptom of vitamin A deficiency. Associated findings include xerophthalmia (conjunctival dryness) and Bitot’s spots (gray-white conjunctival plaques). The patient may complain of visual blurring or vision loss. His skin may be dry and scaly. His mucous membranes may be shrunken and hardened.
Other causes
Drugs
Isotretinoin, used to treat inflammatory acne, rarely causes night blindness.
Special considerations
Because any visual impairment is frightening to the patient, provide emotional support. Help decrease his anxiety and enhance cooperation by explaining scheduled diagnostic tests such as electroretinography in simple terms. Make sure the patient is safe; explain that he shouldn’t drive and that he should use assistive devices at night or in darkened or dim lighting as necessary.
Pediatric pointers
Because children generally don’t have adequate body reserves of vitamin A, they’re especially prone to deficiency and resulting night blindness.
Geriatric pointers
Night blindness due to vitamin A deficiency usually occurs in elderly and disadvantaged patients. It’s also a common effect of aging.
Book Source Details
- Book Title: Professional Guide to Signs & Symptoms (Fifth Edition)
- Author(s): Springhouse
- Year of Publication: 2006
- Copyright Details: Professional Guide to Signs & Symptoms (Fifth Edition), Copyright © 2006 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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