Night blindness: causes, symptoms, diagnosis and treatment

Night blindness, known medically as nyctalopia, is the inability to see well at night or in poor light. People with night blindness find their vision blurred in the dark or in dimly lit places. It is not a disease in itself but a type of visual impairment, a sign of an underlying problem, and it is quite different from total blindness. It is common, for example, for people with myopia (short-sightedness) to notice it, in which case it is an optical problem rather than a disease of the retina. Many causes of night blindness, including vitamin A deficiency, are treatable and reversible.

What causes night blindness?

The problem lies with the cells of the retina that let you see in low light, or with the light reaching them. Causes include:

1. Cataract: the eye's natural lens becomes cloudy and lets less light through, and eventually blocks it. See cataract surgery.
2. Myopia (short-sightedness): uncorrected short sight commonly makes vision worse at night.
3. Medicines: some drugs, such as certain glaucoma medicines, narrow the pupil and reduce the light that enters the eye.
4. After LASIK: reduced night vision and halos around lights are occasional side effects of LASIK surgery. Before LASIK, a test is done to assess how likely this is. Read more about LASIK surgery.
5. Diabetes: poorly controlled diabetes can cause diabetic retinopathy, in which damage to the tiny blood vessels that supply the retina harms it. This is a more serious cause.
6. Vitamin A deficiency: without enough vitamin A, rhodopsin, the light-sensitive pigment in the retina's rod cells, cannot be replenished. Contrary to popular belief, this is a less common cause than those above.
7. Zinc deficiency: zinc is a co-nutrient the eyes need in order to use vitamin A.
8. Too much sun exposure: excessive sunlight can harm the retina and reduce night vision.

Nutrients linked to night blindness

• Zinc: zinc is needed to transport vitamin A from the liver to the retina. Zinc supplements can help improve night vision, especially in people who are deficient.
• Vitamin A: where vitamin A deficiency is present, it is often behind the night blindness, and night blindness is one of the commonest symptoms of vitamin A deficiency.

Symptoms

The main symptom is difficulty seeing at night or in dim light, with vision becoming blurred in the dark or in poorly lit places. Other symptoms depend on the cause; after LASIK, for example, some people notice halos around lights.

Diagnosis

Because night blindness is a sign of another problem, diagnosis means finding the cause. An ophthalmologist (eye specialist) will examine your eyes, including the lens and the retina, check your spectacle power, and ask about your medicines and general health, such as diabetes and diet. See what a comprehensive eye examination includes.

Treating night blindness

1. Treating poor night vision usually means treating the underlying condition.
2. Myopia is corrected with glasses or contact lenses.
3. Cataract surgery, a simple operation, removes the cloudy lens, improves vision and reduces night blindness.
4. Medicines that can cause night blindness, such as quinidine, may be replaced with another medicine by your doctor.
5. People who lack vitamin A should eat more foods rich in it. See nutrition and diet for healthy eyes.
6. For people who are born with the condition, night blindness is lifelong, as there is currently no cure.

If you find it increasingly hard to see when driving at night, read our guide to night driving glasses, and have your eyes examined first.