The total solar eclipse is coming, and as the excitement builds, so does the worry that it will leave behind a nation of eye problems.
The spectacular sight of the moon covering the sun will be visible across North America for the first time in almost a century on Monday.
We’ll all be tempted to gaze up at the sky, but many people don’t realize they can get hurt by staring directly at the sun without the proper protection, said Dr. Russell N. Van Gelder, professor of ophthalmology at the University of Washington School of Medicine.
“The danger is real for permanent vision loss,” Van Gelder, a clinical spokesman for the American Academy of Ophthalmology, told TODAY.
“It’s a big deal for us. We don’t have a lot of public health issues in ophthalmology where we’re really worried about things that threaten the eye health of the population … But this is an event that really hundreds of millions of people are going to be exposed to.”
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Even if one-tenth of 1 percent of people ignore the warnings, there could be thousands of Americans who lose some vision, he noted. Children are at highest risk.
Here’s what you need to know:
Why your eyes are in danger
You may remember taking a magnifying glass outside as a kid on a sunny day and burning a hole in a leaf or starting a small fire. It takes just a few seconds for the smoke to start.
Your eye is basically a very powerful magnifying glass, Van Gelder said. If you stare at the sun, you’re focusing all the energy of that light onto your retina, the light-sensitive tissue in the back of your eye, and essentially burning a hole. You won't feel it because the retina doesn’t have any pain fibers, but the damage can happen after a few seconds.
We all have a natural aversion to staring at very bright lights, but we also have the ability to overcome it.
“The worry in the eclipse is that people are so interested to see one of the great astronomic spectacles that they will suppress their inner drive to look away from the very bright light,” Van Gelder said.
How your vision could be affected
The damage is known as solar retinopathy. That can include blind spots, distortions or loss of contrast in your central vision, which is what you use to read, drive and work on the computer.
There have been reports of people becoming legally blind in at least one eye after watching eclipses, Van Gelder said.
Studies show about one-quarter of patients who develop solar retinopathy suffer permanent damage, he added.
Sunglasses will not protect you
Regular shades will “absolutely not” defend your vision from the sun’s powerful rays, Van Gelder warned. Even the darkest sunglasses do not reduce the amount of light hitting the back of your eyes by that much.
“They’re not an acceptable means for protecting your retina,” if you stare directly at the sun, he said.
What to look for in eclipse viewing glasses
These glasses have special-purpose solar filters, like Mylar, and wearing them may mean a million-fold decrease in the amount of light getting into the eye, Van Gelder said.
“These glasses basically turn day to night,” he noted.
You must look for glasses that meet the ISO 12312-2 international standard for such products, NASA advises. You can buy the glasses online — the cardboard-frame versions cost just a few dollars — but check the American Astronomical Society's list of reputable vendors first. You can also get glasses from your local library.
Wear the glasses any time you want to look at the sun, even if there’s only a small sliver of the star peeking behind the moon in a partial eclipse. That little sliver is still as bright and damaging as looking at direct sunlight, Van Gelder said.
When it’s OK to look at the eclipse with the naked eye
It’s only safe if you are in the thin path of totality, which will pass through parts of 14 states, AND during the brief time when the moon fully eclipses the sun, when day turns into night, Van Gelder said.
The instant the totality is over, immediately look away and put the special glasses back on. Don’t walk or drive in them because you won’t see much.
“My strong, strong advice is take the two minutes to order the glasses for yourself and your family and then enjoy the eclipse without worrying that you’re going to blind yourself by looking at it,” Van Gelder said.
This article originally appeared on TODAY Health & Wellness.