“Keep your eyes on the stars, and your feet on the ground,” Theodore Roosevelt famously advised. But what if you gaze up and those once-twinkling stars are blurry, have halos, or aren’t even visible? You may be one of millions of people with nyctalopia, otherwise known as night blindness.

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What Causes Night Blindness 

Nyctalopia itself is not a disease or syndrome. You might have excellent vision in the light, but as it gets darker you can’t distinguish colors and things aren’t as clear, says Robert Africano, O.D., an optometrist at North Carolina Primary Vision Care Associates inside America’s Best in Charlotte, N.C., and an NVI University ambassador.

Objects in motion are easier to see than stationary ones. One study of people with 20/20 vision during the day found that they dropped, on average, one and a half lines on the eye chart in dusky conditions and almost three lines in simulated darkness.

Dr. Africano says that night blindness becomes a medical problem if it interferes with normal activities such as driving, if it puts your health or safety at risk, or if it seems to keep getting worse. Symptomatic night vision loss can be caused by many conditions, including:

Cataracts. These are the result of proteins in the eye breaking down and clumping together, clouding the normally clear lens of your eye. Seeing through cataracts is like looking through a frosted window, often with a yellow or brown haze. Cataracts tend to get larger with age, potentially causing double vision, poor night vision, and excessive glare from lights.

Nearsightedness. People with nearsightedness, or myopia, can see close objects clearly but have trouble focusing on objects in the distance. Some people with myopia experience extra blurriness at night.

Aging. “The more birthdays you have, the more susceptible you are to night vision problems—even if your daylight vision is OK,” says Dr. Africano, adding that he sees more night vision complaints among his older patients. Once you hit your 50s, aging brings a gradual reduction in the size of the pupil (so less light hits the retina) and a decrease in the number of rods in the retina (the cells that control twilight-and-night vision). Contrast sensitivity is also reduced, which makes it more difficult to discern objects in the dark.

Eye disease. Almost any disease that causes the retina to deteriorate, including macular degeneration, retinitis pigmentosa, glaucoma, or diabetic retinopathy, can contribute to low night vision and/or tunnel vision. The reason: Specific cells in the eye’s retina allow you to see in dim light, says Joseph Kaspareck, M.D., an ophthalmologist affiliated with the Robert Wood Johnson Medical Center in Somerville, N.J. If these fragile cells become damaged, so will your ability to see clearly in the dark.

Corrective surgery. Some people who have had refractive surgery for vision correction, such as PRK or LASIK, can experience vision distortion and night blindness, especially during the healing process. One survey of people who’d had corrective eye surgery found that 25 percent reported worse night vision than before, even though their day vision improved.

Vitamin deficiency. Rarely, deficiencies in certain nutrients, especially vitamin A, can cause poor night vision. People who have had weight reduction surgery should be especially conscious of night vision loss, because these procedures can affect the body’s ability to absorb and metabolize vitamin A.

Recommended reading: 6 Common Reasons You Have Trouble Seeing Well at Night

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What to Do About Night Blindness 

If you’re not sure if you have night blindness that requires medical attention or just normal poor night vision, ask yourself these questions:

• Do you have trouble moving about the house at night, even with a night-light on? 
• When driving, do you see more glare than usual in oncoming headlights? 
• Do you avoid nighttime activities because of your poor vision? 
• Do you have trouble recognizing familiar faces in the dark?
• Does it take your eyes a long time to adjust to light when coming in from the darkness?

If you answer yes to any of these questions, it’s a good idea to make an appointment with your eye doctor right away. They will give you a thorough eye exam to try to determine the cause of your night vision loss.

Treatment for night blindness will depend on the cause. If your poor night vision is caused by a change in your level of refractive error, which determines your eyeglass and contact lens prescription, the solution could be as easy as a new prescription, says Dr. Africano. If cataracts are the cause, you may be a candidate for a routine surgery that replaces the cloudy lens with a clear one. Other causes may not be so easy to resolve, and some people will have to change their lifestyle or work schedule to get around their diminishing sight.

“Night blindness is often a nuisance, but in some cases it can really interfere with daily living,” says Dr. Kaspareck.