Seriously, you don’t want to damage your eyes while observing the highly anticipated Aug. 21 event.

You know not to look directly at the sun.

But what about when there’s a once-in-a-lifetime event like next month’s solar eclipse?

On Aug. 21, the first total solar eclipse to travel across the entire United States since 1918 will be seen by millions of people as it slides across 14 states.

As excitement surrounding this rare celestial event builds, many people are planning their day around when they can look directly at the sun.

However, NASA officials have a warning.

People need to take steps to keep their eyes safe, or they will risk vision loss.

And simply trying to squint at the sun during the eclipse is not a good way to protect your eyes.

Staring at the sun with unprotected eyes can lead to solar retinopathy, which occurs when too much ultraviolent light floods the retina and damages the eye.

There are special glasses you can get that will protect your eyes, and we’ve included NASA’s checklist for ensuring your viewing glasses are safe:

  • Have certification information with a designated ISO 12312-2 international standard.
  • Have the manufacturer’s name and address printed somewhere on the product.
  • Avoid using the devices if they are older than three years or appear damaged or wrinkled.
  • Do not use your own homemade filters.
  • Regular sunglasses are no good, no matter how dark your lenses.

“While NASA isn’t trying to be the eclipse safety glasses ‘police,’ it’s our duty to inform the public about safe ways to view what should be a spectacular sky show for the entire continental United States,” Alex Young, associate director for science in the Heliophysics Science Division at NASA’s Goddard Space Flight Center in Maryland, said in a statement.

The cost of not getting the right glasses can mean serious or permanent vision loss.

Dr. Nathan Podoll, assistant professor of clinical ophthalmology at the Vanderbilt Eye Institute, said permanent damage to the retina can occur after looking at the sun for just seconds without protective lenses.

“It doesn’t do such a great job of repairing itself,” Podoll said of the retina. “We can’t regrow or medicate or repair it.”

Permanent vision damage can include “blind spots” and in extreme cases blindness due to the intensity of the light.

Children’s eyes can be at increased risk, since their lens are less likely to be as opaque as in older people’s eyes.

The eclipse may be especially dangerous for the millions of Americans just outside the path of the total eclipse in areas where the sun will only be partially obscured.

Podoll explained that many people think staring at the sun before and after a total eclipse is safer because the sun is partially obscured.

But NASA warns that staring at the sun is still a bad idea even if it is partially obscured.

“Even when 99 percent of the sun’s surface [the photosphere] is obscured during the partial phases of a solar eclipse, the remaining crescent sun is still intense enough to cause a retinal burn,” NASA officials said on their eclipse website.

Another thing to remember is that the retina has no pain receptors, so you may not realize you’ve damaged your vision until it’s permanent.

If you can’t see the eclipse in person you can see NASA’s livestream of the event — no eye protection required.

Since Podoll lives in Tennessee, he’s in the path of “totality” where the moon will completely block out the sun for a few minutes.

He plans on stepping outside to watch it firsthand, and advises others to do the same if they have appropriate protective gear.

“From what I understand it’s quite spectacular,” he said.