MARYVILLE, Tenn. (WVLT) -- Eyes all across the country are focused on August 21, but be careful watching history in the making.
"When you think about it, on a very sunny day and you look at the sun for like five seconds, and it can cause pain," said Blount County Eye Center optometrist Dr. Will Tantum. "During an eclipse, people are looking at the sun for minutes at a time without looking away."
The total solar eclipse shouldn't take more than three or four minutes, and the moon blocks some of the sun's brightness. Still, Dr. Tantum warns staring at the sun that long without protection can be dangerous.
"They don't realize all the radiation that's entering their eyes," he said.
The radiation can burn the eye's retina. Once the damage is done, there's a chance it can't be reversed.
"Most people would probably notice it the next day when they woke up and looked in the mirror in the bathroom, their vision would be really blurry," he said. "Only time will tell whose will go away and whose will be permanent. There's no way to tell."
NASA urges anyone who wants to watch the eclipse to get their hands on a pair of International Organization of Standardization (ISO) approved eclipse glasses.
"These block out a lot more light than a pair of sunglasses do," said Dr. Tantum. "It's kind of like looking through tin foil, it's amazing how much they block out."
"Nothing," said Joe Gregory while he tried on the approved eclipse glasses on a sunny day. "The sun looks like an orange ball. Everything is black except for the sun. I can't even see you right now."
Even polarized sunglasses let too much radiation pass through. To compare, Dr. Tantum tested a pair of sunglasses and eclipse glasses. Eclipse glasses were the only ones to block out all radiation.
If viewers watch the eclipse in the path of totality, NASA recommends removing your viewing device only when the moon completely covers the sun's face. As soon as the sun begins to appear again, put the glasses back on.
NASA also notes that people who wear glasses should keep them on underneath the eclipse glasses.
Do not look a the sun through a camera, telescope or binoculars. NASA advises the concentrated solar rays will damage the eyes and potentially cause serious injury.
Most East Tennesseans won't want to miss a moment of something that only comes around once in a lifetime and passes over hometown skies. Dr. Tantum just wants to be sure everyone can see clearly once it passes, too.
Blount County Eye Center in Maryville is handing out free ISO approved eclipse glasses while supplies last.
SAFE ALTERNATIVES TO ECLIPSE GLASSES:
Welder's glass with #14
Telescopes with solar filters
Pinhole projection methods