Before You Watch the Solar Eclipse, Make Sure Your Glasses Pass This Test

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On Wednesday, August 12, millions of Americans will have the chance to watch a partial solar eclipse. From Alaska to North Carolina, viewers will see the moon take a small bite out of the sun. Meanwhile, eclipse chasers hoping to experience totality are traveling to Greenland, Iceland, and Spain.

If you're trying to catch the partial eclipse, it's important to be prepared. To help make sure you're set for the big day, I spoke to two experts about eclipse glasses and safety, including:

• Jody Piltz-Seymour , M.D., an ophthalmologist and director of the Glaucoma Care Center at Valley Eye Professionals.

• Alec Scherma , senior mechanical engineer at the Good Housekeeping Institute.

Choosing proper eclipse glasses

According to Dr. Piltz-Seymour, regular sunglasses cannot be used to view an eclipse, and doing so would be extremely dangerous.

Instead, she advises to only use eclipse glasses with an ISO 12312-2 rating , a designation that comes from the American Astronomical Society . The ISO rating is the standard for any product designed to allow you to look at the sun, including these glasses.

"The filter essentially blocks 99.999% of intense visible light from the sun itself (allowing just enough that you're not tempted to take the glasses off for a better view), and also blocks 100% of ultraviolet and 100% of infrared light," Dr. Piltz-Seymour explains.

NASA has never endorsed a brand of solar eclipse glasses, so if you see "NASA-approved" language on a product, it's best to skip it. For all of the glasses linked in this story, I researched the manufacturer's websites and verified that they indeed have the ISO 12312-2 certification posted.

"The safety of eclipse glasses is entirely a function of the filter film, so either affordable cardboard or hard plastic frames are both safe as long as the film meets the standard," Dr. Piltz-Seymour continues.

In my experience, the plastic frames are typically more durable and might be easier to wear, but as long as you get anything with the ISO 12312-2 rating, that's what matters the most.

How to check your eclipse glasses

It only takes a couple of minutes to check your glasses for safety. Our experts share a few tips:

1. Look for the ISO rating.It should be printed directly on the frame of the eclipse glasses.

2. Check for any scratches or punctures on the actual lens:"Any perforation to the lens could cause harm to your eyes if you look at the sun directly with them," Scherma says. And if the lenses are coming loose from the plastic or cardboard frames, don't use them at all.

3. Practice wearing the glasses beforehand, especially if you're watching with kids.Scherma says the glasses should stay securely in place when you tilt your head up and down. Before the 2017 total solar eclipse, I practiced with my two little ones ahead of time because I knew they'd be tempted to play with their glasses. By the time we stepped outside, they knew exactly what to do.

4. Test them indoors.When wearing the glasses inside, you should be in near-complete darkness, with only a faint glow from bright lights being visible.

5. Make sure to wear them during the entirety of the eclipse.Dr. Piltz-Seymour says, "Be sure to put your glasses on before looking up at the sun and remove them only after looking away from the sun. When the eclipse is partial, eclipse glasses must be used at all times." Scherma adds, "You should see the sun very clearly defined but at a comfortable brightness. If it isn't defined, look away, as you may have a pair of bad glasses."

6. If you wear prescription glasses, put your eclipse glasses over your regular pair—not underneath.

Looking directly at a solar eclipse can cause serious harm

There can be serious consequences to looking directly at a solar eclipse, including solar retinopathy (damage to the retina at the back of your eye), or worse. Dr. Piltz-Seymour explains that the intense brightness of the sun can overwhelm the light-sensing rods and cones in your retina. This causes a chain of chemical reactions that injures them, or thermal damage that burns the retina. She cautions that this damage can cause permanent blind spots and irreversible vision loss.

Never use the naked eye nor eclipse glasses with binoculars, telescopes, or camera lenses—these require a special filter

Binoculars, telescopes, and cameras concentrate the sun's light and can overwhelm the filters, potentially causing serious eye damage. "These are built to increase the amount of light going through, which is why you can see far things close-up and defined," Scherma explains.

Dr. Piltz-Seymour also notes that this concentrated light could damage the lenses on your glasses, making them useless.

Instead, look for specialized eclipse filters for your devices, like this telescope filter , that go over the front lens (not over the eyepiece), and you should look for the same ISO 12312-2 certification.

Below are a few more glasses that are rated ISO 12312-2 by the AAS for viewing the eclipse. P.S., If you can't make it overseas for the totality, NASA will be showing the whole thing online!

Medical King Solar Eclipse Glasses, 5-Pack

AAA Eclipse Solar Eclipse Glasses, (6-Pack)

Soluna Solar Eclipse Glasses, (2-Pack)

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