Night Blindness (Nyctalopia): Causes, Tests and Night Driving

Most of us take a short moment to adjust when we walk from a bright room into the dark. For some people, though, that adjustment takes much longer, or dim light never becomes comfortable at all. Stars disappear, a darkened cinema becomes an obstacle course, and driving after sunset feels risky. This difficulty seeing in low light is called night blindness, or nyctalopia.

Night blindness is not a disease in itself but a symptom with many possible causes. Some are simple to correct, such as an out-of-date glasses prescription or a cataract. Others, like vitamin A deficiency or inherited retinal disease, need specific diagnosis and care. This guide explains how night vision works, the main causes of night blindness, how it is investigated, what can be done, and how to stay safe on the road after dark.

How night vision works

The retina contains two types of light-sensitive cells. Cones work in bright light and give sharp, colour vision. Rods are far more numerous, are concentrated outside the central retina, and are extremely sensitive to low light, but they do not see colour or fine detail. In dim conditions we rely mainly on rods, which is why colours fade and we see faint objects better slightly to the side than straight on. Our guide to how vision works describes this in more detail.

Rods contain a pigment called rhodopsin, which is built from a protein and a form of vitamin A. Bright light breaks rhodopsin down; in the dark, the eye gradually rebuilds it. This process, called dark adaptation, takes around 20 to 30 minutes to reach full sensitivity. Anything that damages rods, limits vitamin A, reduces the light reaching the retina, or blurs the image can impair night vision.

Main causes of night blindness

Myopia and refractive errors

Short-sightedness is one of the most common reasons people feel they cannot see well at night. When the pupil widens in darkness, more of the edge of the eye's optics comes into play, which increases blur. Some people have a small extra shift towards myopia only in the dark, sometimes called night myopia. Distant street lights, signs and road markings become fuzzy or star-shaped. An eye test and accurate, up-to-date glasses or contact lenses often bring a dramatic improvement. Uncorrected astigmatism can also cause streaks and starbursts around lights. Read more in our myopia guide.

Cataract

A cataract is a clouding of the natural lens inside the eye, most often related to ageing. Even before it seriously affects daytime reading, a cataract scatters light from oncoming headlights, causing glare, halos and a sense that the windscreen is dirty. Night driving is often the first activity people give up. Cataract surgery replaces the cloudy lens with a clear artificial one and is one of the most effective operations in medicine. See our guide to cataract.

Glaucoma medicines and other drugs

Some older glaucoma treatments, especially pilocarpine-type drops (miotics), work by constricting the pupil. A small pupil lets in less light, so the world looks darker in dim conditions. Today these drops are used less often for glaucoma, but pilocarpine eye drops have also been approved in some countries to improve near vision in presbyopia, and night vision warnings apply to them as well. Never stop a glaucoma treatment yourself; discuss side effects with your doctor, who may switch to another drug class. Other medicines, including some used for malaria, rheumatic disease or psychiatric conditions, can affect the retina over time. See medications that affect the eyes.

Advanced glaucoma itself can also reduce vision in dim light because it damages the optic nerve and narrows the field of view.

Vitamin A deficiency

Vitamin A deficiency is the classic cause of night blindness and remains a serious public health problem worldwide. According to the World Health Organization, it is the leading cause of preventable childhood blindness, especially in parts of Africa and South Asia, and night blindness during pregnancy is also common in affected regions. Night blindness is often the earliest symptom. If the deficiency continues, the surface of the eye dries out (xerophthalmia), foamy grey patches called Bitot spots appear on the white of the eye, and eventually the cornea can soften and ulcerate, leading to permanent blindness.

In countries with varied diets, vitamin A deficiency is uncommon, but it does occur in people with:

• Malabsorption conditions, such as coeliac disease, Crohn's disease, cystic fibrosis or chronic pancreatitis.
• Bariatric (weight-loss) surgery, particularly bypass procedures.
• Liver disease or heavy alcohol use.
• Very restrictive diets or eating disorders.

Treatment is with vitamin A under medical supervision, and early night blindness usually reverses. Taking high-dose vitamin A supplements without a deficiency is not helpful and can be harmful: excess vitamin A can damage the liver and bones and can cause birth defects in pregnancy. Food sources include liver, eggs, dairy, oily fish and orange or dark green vegetables containing beta-carotene. Our article on vitamin A and night vision explores this in depth.

Retinitis pigmentosa and inherited retinal diseases

Retinitis pigmentosa (RP) is a group of inherited conditions in which rod cells, and later cones, gradually stop working. Night blindness is typically the first symptom, often starting in childhood or adolescence, followed by slow narrowing of the side vision (tunnel vision). Central vision may be preserved until late. Other inherited conditions, such as congenital stationary night blindness, cause lifelong night blindness that does not progress, while some rare disorders, such as gyrate atrophy or Refsum disease, are linked to metabolic problems. Diagnosis needs specialist testing and often genetic testing; a gene therapy is approved for one specific form (RPE65-related disease), and research into other treatments is active. See our guide to retinitis pigmentosa.

Other causes

• Diabetic retinopathy and laser treatment for it, which can reduce rod function.
• Previous refractive surgery, which in some people causes glare and halos at night.
• Keratoconus and corneal scarring, which scatter light.
• Ageing: pupils get smaller and the lens yellows, so older adults need much more light than young people, even with healthy eyes.

How night blindness is diagnosed

Your optometrist or ophthalmologist will ask when the problem started, whether it is getting worse, about your diet and medical history, medicines, and any family history of eye disease. Examination usually includes:

• Visual acuity and refraction to check for uncorrected myopia or astigmatism.
• Slit-lamp examination of the cornea and lens for cataract or dryness.
• A dilated retinal examination.
• Visual field testing to look for peripheral loss.

Depending on findings, further tests may include dark adaptation testing, electroretinography (ERG), which measures the electrical responses of rods and cones, retinal imaging, blood tests for vitamin A levels and genetic testing. Our guide to eye examinations explains these tests.

Treatment and management

Treatment targets the cause:

• Updated glasses or contact lenses for refractive errors, sometimes with a separate night-driving prescription.
• Cataract surgery when glare and dim vision affect daily life.
• Medication review for drugs that narrow the pupil or affect the retina.
• Vitamin A replacement and treatment of the underlying absorption problem in deficiency.
• Specialist care, low-vision support, genetic counselling and access to clinical trials for inherited retinal disease.

Practical steps also help: use brighter, well-distributed lighting at home, place night lights on the route to the bathroom, mark steps with contrasting tape, and carry a small torch when out after dark.

Driving at night safely

Night driving combines low light, glare from headlights and reduced contrast, so it exposes even mild eye problems. If you struggle, consider these steps:

1. Get your eyes checked and make sure your prescription is current. Many countries require drivers to meet minimum vision standards; if you are unsure whether you meet them, stop driving until checked.
2. Keep glass clean, inside and out, including glasses and headlights; dirt and smears multiply glare.
3. Avoid tinted lenses at night. Sunglasses and yellow night-driving glasses reduce the light reaching your eyes and have not been shown to improve night driving performance.
4. Consider anti-reflective coatings on your glasses to reduce reflections.
5. Look slightly to the right (in right-hand traffic; to the left in left-hand traffic) towards the road edge rather than directly at oncoming headlights.
6. Reduce dashboard brightness and give yourself time to adapt after leaving bright places.
7. Plan routes on well-lit roads, slow down, and avoid driving when tired.

Our article on night driving: glare, halos and vision offers more detail.

When to see a doctor

Book an eye examination if you notice that you see poorly in dim light, take a long time to adjust to darkness, have increasing glare from headlights, or have stopped driving at night. Children who are frightened of the dark or stumble in dim rooms more than their peers, especially if relatives have retinal disease, should also be checked.