Illuminating night blindness

Illuminating night blindness

Dangerous blurry scene of cars, street lights, headlights seen through car window at night; concept of night blindness

Animals known for their excellent night vision include owls, cats, tarsiers (a small primate from Southeast Asia), and even dung beetles.

But what about humans? Not so much.

Over time, many people develop night blindness, also known as night blindness. This condition makes it difficult to see in dim or dark environments because your eyes cannot adjust to changes in brightness or detect light.

What are the dangers for people with night blindness?

Night blindness is especially problematic and dangerous when driving. Your eyes are unable to adjust between darkness and the headlights of oncoming vehicles, other vehicles may appear out of focus, and your depth perception is impaired, making it difficult to judge distances.

Night blindness can also affect your vision at home, making it difficult for your eyesight to adjust quickly to a dark room when the lights are turned off. “This can cause people to bump into furniture or trip and get injured,” said Dr. Isabel Deakins, an optometrist at the Harvard-affiliated Massachusetts Eye and Ear Infirmary.

What happens in the eyes that causes night blindness?

The ability to see in low-light conditions involves two structures of the eye: the retina and the iris.

The retina is located at the back of the eye and contains two types of light-detecting cells called cones and rods. Cones are responsible for color vision and fine detail, while rods are responsible for vision in dim light.

The iris is the colored part of the eye. It contains muscles that widen or narrow the pupil opening to regulate the amount of light entering the eye.

If the iris doesn’t respond properly, the pupil can dilate and let in too much light, causing light sensitivity and making it difficult to see in bright light. Or your pupils may still be too small, leaving you with insufficient light, making it difficult to see in low light.

What causes night blindness?

Night blindness is not a disease but a symptom of other diseases. “It’s like having a bruise on your body. It’s from something else,” Dr. Diggins said.

Several conditions can cause night blindness. For example, medications such as antidepressants, antihistamines, and antipsychotics can affect pupil size and the amount of light that enters the eye.

Eye conditions that may cause night blindness include:

  • Glaucoma, a disease that damages the optic nerve and blood vessels of the eye
  • Cataracts, cloudy areas in the lens that distort or block light from passing through the lens
  • Dry Eye Syndrome.

However, age is a factor that increases the risk of night blindness and cannot be controlled. “As we age, our eyes respond less and less to changes in light, and vision naturally declines over time,” Dr. Diggins said. “The number of rod cells in our eyes decreases, the pupils become smaller, and the iris muscles become weaker.”

What helps if you have night blindness?

If you notice any signs of night blindness, avoid driving and get checked by an eye care professional such as an optometrist or ophthalmologist. An eye exam can determine if your eyeglass prescription needs updating.

“Often, a change in prescription is enough to reduce glare when driving at night,” says Dr. Diggins. “You may even need separate glasses with stronger vision that you only wear when driving at night.”

Adding anti-reflective coatings to lenses may help reduce glare from oncoming car headlights. However, don’t buy the over-the-counter polarized driving glasses sold at many drug stores. “These may help reduce glare, but they don’t address the cause of night blindness,” says Dr. Diggins.

Eye exams can also detect glaucoma or cataracts, which are treatable. Glaucoma treatments include eye drops, laser therapy, or surgery. Cataracts can be corrected through surgery to replace the cloudy lens with an artificial lens. Your eye care professional can also help identify dry eye symptoms and recommend treatment.

Ask your primary care clinician or pharmacist if any medications you take may cause night blindness. If so, the dose may be adjusted or another medication may be used.

Three more ways to make night driving safer

You can also take steps to make driving at night safer. For example:

  • Clean eyeglass lenses regularly. Then take them to an optical shop to have minor scratches polished off.
  • Keep both sides of your car’s front and rear windshield clean so you can see as clearly as possible.
  • Dim dashboard lights that cause glare and use the night setting on your rearview mirror.

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