Night blindness: causes, treatment, and when new glasses are enough

Night blindness is not a disease in itself but a sign: your vision gets worse in the dark or in dim light than it should. Many of its causes can be treated. MedlinePlus, the medical encyclopedia of the US National Library of Medicine, puts cataracts, nearsightedness, some medicines and vitamin A deficiency in that group, and calls the deficiency rare. Some causes are inherited and have no cure yet. The American Academy of Ophthalmology says there are no home treatments or exercises that improve night vision. So the right step is a complete eye exam to find the cause, and no night driving until your eye doctor says it is safe. If your problem is specifically glare from car headlights, the blog has a separate guide to night driving.

How the eye sees in the dark, and how to tell you have a problem

The American Academy of Ophthalmology explains that the pupil widens in the dark to let in more light, and that night vision relies on retinal cells called rods. Rods are far more sensitive than the cone cells that handle color, but they see only in black and white. That is why colors fade at night for everyone, and that part is normal. Rods also cluster toward the edge of the retina, and if they stop working because of disease or injury, night vision is lost. MedlinePlus lists signs worth paying attention to, including:

• Trouble driving at night, or trouble seeing the stars on a clear night.
• Trouble walking through a dark room, such as a movie theater.
• Vision that is worse just after leaving a brightly lit place, or, in milder cases, a harder time adjusting to the dark.

The Academy adds that poor night vision raises the risk of falls and makes safe driving harder, and that worsening night vision can be a sign of a serious eye disease, a temporary effect of another condition or a natural part of aging. You cannot tell which one it is on your own.

Causes that can be treated: from glasses to medicines

• Old glasses or uncorrected nearsightedness: the Academy says that if you need glasses or contacts, or a new prescription, your night vision will be blurry just like your daytime vision. It also notes that some people become more nearsighted in the dark as the pupil widens, which makes distant objects look fuzzy. That can mean you need glasses or a change in lens power. This is the case where new glasses are enough.
• Cataracts: the Academy says that trouble seeing or driving at night can be one of the first symptoms, along with more glare and halos around lights. The US National Eye Institute notes that more than half of Americans aged 80 or older either have cataracts or have had cataract surgery. The treatment is surgery that replaces the cloudy lens with an artificial one.
• Some medicines: MedlinePlus lists them among the treatable causes. Tell your doctor about everything you take, and do not stop a medicine on your own.
• Vitamin A deficiency: the World Health Organization says night blindness is one of its first signs. It is common in developing countries and rare in developed ones. EyeWiki, the Academy's medical encyclopedia, notes that in developed countries the leading causes are pancreatic, liver and intestinal disease, and that in the United States it usually involves a problem absorbing food, such as inflammatory bowel disease or gastric bypass surgery, or a severely restricted diet. With prompt high-dose treatment prescribed by a doctor, the night blindness can clear completely in about 2 months.

Causes that glasses cannot fix

Some causes of night blindness are in the retina itself, and glasses cannot fix them. The best known is retinitis pigmentosa. Despite its name it is not an inflammation but a group of rare inherited diseases in which retinal cells slowly break down. The US National Eye Institute says its most common early symptom is loss of night vision, usually starting in childhood. Parents may notice that a child has trouble moving around in the dark or adjusting to dim light. Side vision then narrows over time.

• Retinitis pigmentosa: the Institute says there is no cure yet, but low vision aids and rehabilitation programs help people make the most of their sight. An eye doctor or genetic counselor can explain the chance of passing it on to children.
• Congenital stationary night blindness: MedlinePlus lists it among the causes that cannot be treated, and the Academy notes that several inherited conditions can reduce or block night vision.
• Glaucoma and macular degeneration: the Academy says both affect daytime and nighttime vision, and early treatment saves as much sight as possible.

Vitamin A: when it helps and when it harms

The World Health Organization estimates that 250,000 to 500,000 vitamin A-deficient children go blind every year, and half of them die within 12 months of losing their sight. It describes the deficiency as a public health problem in more than half of all countries, especially in Africa and South-East Asia. That does not mean everyone whose night vision is weak needs vitamin pills. According to MedlinePlus:

• Males aged 14 and over need 900 micrograms a day and females 700 micrograms, rising to 770 during pregnancy and 1,300 while breastfeeding for women aged 19 to 50.
• Its richest sources are liver, some fish such as herring and salmon and cod fish oil, eggs and dairy, orange and yellow fruits and vegetables such as carrots, sweet potatoes and mangoes, and dark leafy greens such as spinach and broccoli. Absorption from vegetables improves with a little fat.
• Too much builds up in the body and causes serious health problems. Chronic poisoning can occur in adults who regularly take more than 33,000 IU a day. Large doses in pregnancy can cause birth defects, and children are more sensitive to it.

The bottom line: if a test confirms a deficiency, the doctor sets the dose and how long to take it, and MedlinePlus advises asking your health care provider how much to take because it is possible to take too much. Even in retinitis pigmentosa, the US National Eye Institute says vitamin A may help slow vision loss in the common forms, but too much can cause liver problems, so the decision belongs to the doctor. Carrots are good food, but they will not improve the eyesight of someone who is not deficient.

What to do now: practical steps

• Book a complete eye exam. MedlinePlus says a complete exam is important to find the cause, which may be treatable, and that you should contact your eye doctor if the symptoms persist or significantly affect your life. The Academy recommends an eye disease screening by age 40, and sooner for anyone with an eye disease or risk factors.
• Prepare answers to the questions MedlinePlus says the doctor may ask: when it started, whether it came on suddenly or gradually, whether glasses improve it, whether you have had eye surgery, which medicines you take, what your diet is like, and whether diabetes runs in the family.
• Do not drive at night until your eye doctor approves, as MedlinePlus advises, and take care in dim places: soft night lights in hallways and on stairs, and a moment for your eyes to adjust to the dark before you walk.
• If you are pregnant, have had weight-loss surgery, or have a bowel or liver condition, tell the doctor, and do not start vitamin A on your own.
• Do not wait for a routine appointment if a dark shadow or grey curtain covers part of your vision, or if flashes of light appear suddenly. The Saudi Ministry of Health lists these among the symptoms of retinal detachment and says to go to an eye doctor or the emergency room immediately.