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Humans aren't always cut out to be creatures of the night

Date:
October 26, 2015
Source:
Saint Louis University Medical Center
Summary:
Nighttime hunters like cats and owls, benefit from their big round eyes that let in plenty of light, but humans have more limited abilities to see in the dark. A new article suggests that poor night vision is a common complaint that can be particularly vexing while driving.
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Owls and cats are at an advantage as the days get darker, but humans may notice their vision takes a hit during their evening commute home as daylight hours shrink.

Nighttime hunters, cats and owls, benefit from their big round eyes that let in plenty of light as well as having lots of rods, a type of photoreceptor, that help them see in low light conditions. (Even they can't see in total darkness.) Humans have more limited abilities to see in the dark, and, at times, can struggle with night vision.

Assistant professor of ophthalmology at Saint Louis University, Matthew Council, M.D., says that poor night vision is a common complaint that can be particularly vexing while driving.

"Difficulty refocusing your eyes between bright lights and a dark stretch of road is normal," Council said. "It's hard for our eyes to do this.

"If you experience more trouble than this, though, or if you notice increasing difficulty with night vision, you may want to consider some possible causes, fixes, or a trip to an ophthalmologist."

Dry eyes, an incorrect eyeglasses prescription, and early cataracts are three very common causes of poor night vision, Council says.

Dry eyes

Dry eyes are a common culprit. If you have symptoms of irritation, dryness, or feel like your eyes have something in them, you may be suffering from dry eyes.

"Both younger and older people can be bothered by dry eyes," Council said. "People don't think a lot about it, but the tear film plays a big role in the quality of vision. This can manifest with trouble seeing at night. Eyes get more dry as the day goes on, and by night, they can really be feeling it.

"This time of year is a bad time for dry eyes, and it tends to get worse once we turn on the heat."

In simple cases, over-the-counter artificial tears may do the trick. If problems persist, your eye doctor may recommend other prescription eye drops.

"Many people have significant dryness in their eyes, and it can be a chronic condition. Things like wearing contacts can contribute, and though it seems minor, it's an important condition to identify and treat early."

Incorrect eyeglasses prescription

A simple problem that can be overlooked happens when someone has an incorrect eyeglasses or contact prescription. Our eyes naturally become a little nearsighted in dim light. If this small effect is compounded by an eyeglass or contact lens prescription that is a bit off, the effect can be magnified.

Similarly, some people have a mild amount of nearsightedness but do not need glasses to function during the day. At night, however, when the effect is magnified, they might benefit from wearing glasses. Many people get glasses for occasional use, like driving at night.

Cataracts

In the early stages of developing cataracts, the first symptom a person notices might be increased difficulty seeing at night. A cataract is a clouding of the natural lens of the eye that can affect vision. Cataracts tend to grow slowly over time.

"Sometimes cataracts begin in early middle age, and difficulty with night vision, dim lighting, or glare is often a first sign," Council said. "Patients are often very bothered by oncoming traffic lights."

If cataracts are taking too big a toll on your vision, they can be corrected with surgery.

"When we decide to do surgery, we're looking to see if it is impacting a patient's life," Council said. "For people who are less bothered by cataracts, we may simply monitor the situation. For those who are losing quality of life, we can perform surgery, removing their cataract and replacing it with a personalized lens, often removing their need for glasses in the process."

Other causes

Less common medical conditions, including certain vitamin deficiencies and retinal diseases, like retinitis pigmentosa (an inherited, degenerative eye disease) also can cause night vision issues. Diabetic retinopathy and glaucoma can damage vision and contrast sensitivity, and can be experienced as a gradual change that sometimes is first noticed as vision difficulty in low light conditions.

While vitamin deficiencies that cause vision problems are uncommon in the developed world, certain medical conditions affecting the digestive tract, like Crohn's disease and celiac disease, can impede absorption of vitamins, and are treated by doctors with vitamin A and zinc supplementation.

What you can do to manage minor night vision issues

In addition to using over-the-counter eye drops for dry eyes, there are some other simple things you can try that often make a big difference, Council says. For starters, if you do wear glasses make sure they are clean. Smudged or scratched glasses can magnify the glare you get from bright lights.

Also, make sure your car's windshield is clean. Don't forget the inside of the windshield, which can accumulate dust.

And, while newer cars have automatically dimming rearview mirrors to help the eyes adjust to bright lights, older cars might have a flip tab that can manually be used to reduce glare. Don't forget to use this feature!

Signs you should see an ophthalmologist

If you've tried some of these simple fixes and you aren't solving your night vision problems, an ophthalmologist may be able to shed more light on the problem and offer additional solutions.

Severe difficulty in low light conditions, sometimes described as night blindness, is usually caused by one of the underlying conditions described above. If, for example, you find yourself stumbling over furniture in the evening because you can't see, it's time for a doctor's visit.

"The time to see an ophthalmologist is when you find that your vision isn't meeting your needs," Council says. "If you seem to be having trouble seeing things at night that other people don't have trouble with, nighttime vision loss that seems out of proportion or is accompanied by loss of normal or daytime vision, or if you experience pain or extreme dryness, that's a signal to come in for a consultation."


Story Source:

Materials provided by Saint Louis University Medical Center. Note: Content may be edited for style and length.


Cite This Page:

Saint Louis University Medical Center. "Humans aren't always cut out to be creatures of the night." ScienceDaily. ScienceDaily, 26 October 2015. <www.sciencedaily.com/releases/2015/10/151026141643.htm>.
Saint Louis University Medical Center. (2015, October 26). Humans aren't always cut out to be creatures of the night. ScienceDaily. Retrieved May 23, 2017 from www.sciencedaily.com/releases/2015/10/151026141643.htm
Saint Louis University Medical Center. "Humans aren't always cut out to be creatures of the night." ScienceDaily. www.sciencedaily.com/releases/2015/10/151026141643.htm (accessed May 23, 2017).

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