Night blindness
Usually difficult to identify, night blindness (or nyctalopia) 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
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.
Physical assessment
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.
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.
Optic nerve atrophy
Optic nerve atrophy 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
Retinitis pigmentosa is usually a hereditary retinal degeneration in which night blindness is characteristically the first symptom, typically 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.
Special considerations
Prepare the patient for diagnostic testing, such as ophthalmoscopy, visual field testing, fluorescein angiography, and electroretinography. Genetic counseling is recommended for adults who risk transmitting hereditary disorders to their children. Vitamin A supplementation and nutritional counseling may improve night vision in some patients.
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.
Patient counseling
Because 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. Ensure patient safety, and explain that the patient shouldn’t drive and should use assistive devices at night or in darkened or dim lighting as necessary.
Pictures
Book Source Details
- Book Title: Signs & Symptoms: A 2-in-1 Reference for Nurses
- Author(s): Springhouse
- Year of Publication: 2007
- Copyright Details: Signs & Symptoms: A 2-in-1 Reference for Nurses, Copyright © 2007 Lippincott Williams & Wilkins.
Other Book Chapters Related to Night blindness
Read excerpts from these other book chapters related to Night blindness:
Medical Books Excerpts
- Vision loss
- "Professional Guide to Signs & Symptoms (Fifth Edition)" (2006)
- [ read ]
- Vision loss
- "Alarming Signs and Symptoms: Lippincott Manual of Nursing Practice Series" (2007)
- [ read ]
- Vision loss
- "Signs & Symptoms: A 2-in-1 Reference for Nurses" (2007)
- [ read ]
Copyright Details: Signs & Symptoms: A 2-in-1 Reference for Nurses, Copyright © 2008 Williams & Wilkins.
More About Causes of Night blindness
» Next page: Vision loss (Nursing: Interpreting Signs and Symptoms)
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