En español | Walking or driving in the dark can be disconcerting for anyone. But for those who experience what's known as night blindness, moving about in poorly lit surroundings is not only unsettling — it can be downright dangerous. Here's what to know about why some people have more trouble seeing in low light than others.
What is night blindness?
Night blindness is a specific kind of vision impairment. It is not a condition or disease in and of itself, but rather a symptom of an underlying problem. “The word is a bit misleading,” says Melissa Yao, M.D., assistant professor in the Department of Ophthalmology & Visual Sciences at Albert Einstein College of Medicine and Montefiore Medical Center, in New York City. “The symptom is not confined to the nighttime, nor does it mean that you're totally blind. The medical term that we use, which is more accurate, is ‘nyctalopia,’ which means the inability to see well in the dark or dimly lit conditions.”
You may notice that you have more trouble recognizing people's faces in darkened settings, worry about tripping and falling while walking inside your home or outside in dark conditions, and can't see as well when driving at night, for instance.
Causes of the condition
A quick anatomy lesson: Light enters the eye through the cornea, passes through the pupil (the tiny opening in the center of the iris), then hits the lens, which focuses light rays onto the retina (the thin, light-sensitive tissue that lines the back of the eye).
The retina has two types of photoreceptors: rods and cones. We use the cones for lighted situations, says Yao. “They allow for sharp vision and for color, but they don't work well in the dark. Therefore, some adaptations occur in our eyes in the dark.” Our pupils open up more for light to get through the lens, for one, and the other photoreceptors, the rods, are activated. Rods don't work as well for color or acuity. (That's why we tend to see mostly in black and white when it's dark.)
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A problem with any portion of this pathway can result in diminished vision in darker settings.
And such problems are often the result of aging. Many of the age-related eye changes that affect daytime vision do the same with nighttime vision. For example, if you have uncorrected nearsightedness, your night vision will be blurry, just like your daytime vision. “You may need glasses or your lens prescription may need to be updated,” Yao says.
Other underlying conditions that may cause nyctalopia include:
- Cataracts. This clouding of the natural lens of the eye can make vision blurry or dim and can increase glare or halos from headlights and streetlights. (Keep in mind that poorly controlled diabetes can cause cataracts, so watch your diet.)
- Glaucoma. “Glaucoma can cause damage to the optic nerve, initially causing difficulty with the peripheral vision, before damaging the central vision,” says Ravi D. Goel, M.D., an ophthalmologist and cataract surgeon in Cherry Hill, New Jersey, and clinical spokesperson for the American Academy of Ophthalmology. Because the outer area of the retina includes more rods than cones, loss of peripheral vision often results in night blindness. What's more, says Yao, older people who are being treated for glaucoma may have problems with night blindness. “A small percentage of glaucoma medication can constrict your pupil,” she says, “so not enough light will get to the back of your retina.”
- Vitamin deficiency. In rare cases, vitamin A deficiency can lead to night blindness. This is because vitamin A is necessary for the creation of a light-sensitive pigment called rhodopsin, located in the rods, which is needed for low-light vision and constantly needs to be replenished. Most of us get enough vitamin A from our diet; good sources include milk, meat, fish, eggs, green leafy vegetables, and yellow fruits and vegetables. But some people may have deficiencies for other reasons — for example, an underlying liver disease. “Vitamin A is metabolized and stored in the liver,” Yao says, “so if you have a liver problem, you may find that you have a lower level of vitamin A.”
You may also be experiencing malabsorption, meaning you're eating enough vitamin A but your body can't absorb it so it's not getting into the bloodstream and being transported to where it needs to go. “We see that in patients who have undergone gastrointestinal surgery, such as intestinal infarctions or also bariatric surgery, or weight-loss surgery,” Yao says. “Because their gastrointestinal tract has been altered, they can't absorb vitamin A as well, because vitamin A is absorbed in the gut.”
How to treat nyctalopia
Schedule an appointment with your ophthalmologist. An eye exam can help find the underlying cause. A vitamin A deficiency can be ruled out with a simple blood test, and the exam can reveal associated symptoms, such as a dry cornea, Goel says. Be sure to bring information about any prior surgery you've had, Yao says, “particularly gastrointestinal surgery, liver problems and symptoms, and your medical history."
Treatment for night blindness will depend on the cause. “A majority of cases are reversible once the cause is identified,” Yao says. “If it's due to cataracts, you can have that conversation with your doctor about whether surgery is necessary at this point. If a vitamin A deficiency is suspected, supplemental vitamin A may be advised. If you're taking a glaucoma medication that's causing a constriction of your pupils, we may need to find alternative medication.”
In the meantime, try to lower your risks of falls or other accidents that can occur with low vision:
- Make your home brighter. "Ensure that you have adequate lighting in the house,” Yao says. “Put in an extra lamp in a room so it's better lit.”
- Clear your path. "Night blindness issues are something that you should not ignore, because it can lead to falling, which has all sorts of consequences, such as hip issues,” Goel says. “There are experts, such as occupational therapists, who can come do in-home assessments for falling.”
- Avoid night driving. Consider driving only during the day and getting a ride from a friend or a ride service at night.
- Wear sunglasses in bright sunlight. "It may take longer for your eyes to adapt from light to dark surroundings,” Yao says. Wearing sunglasses allows for a less-abrupt transition from brightness into a dimly lit setting (where you'd immediately take off the sunglasses), helping your vision adjust more quickly.