The day of the long-awaited coast-to-coast solar eclipse has all but arrived — and if history is any guide, it's likely that somebody's eyes are going to get hurt.
"The ones we're really concerned about are the people who have never seen an eclipse before — or just decided that, you know, 'Today is a nice day to go take a look at a solar eclipse' — and, 'Oh, I probably don't need to do very much to get ready to do that.' Then I get worried," says Ralph Chou, an optometrist and vision scientist at the University of Waterloo in Canada. He has seen 18 total solar eclipses.
You really can get blurred vision or blind spots after watching partial eclipses without protection, says Chou, even if there's just a tiny little crescent of sun left in the sky.
"I've seen a couple of patients over the years where, you know, you've got very distinct crescent-shaped scars from looking at a solar eclipse," says Chou.
It is never safe to look directly at a partial eclipse without special eclipse glasses or filters — and most of the country will see only a partial eclipse.
The risk of injury to the eye's retina is even greater if you if you look at a partial eclipse without protection through a telescope or binoculars, Chou warns.
"The damage," he says, "can happen extremely quickly."
Binoculars and telescopes need special filters — it is not safe to look through them while just wearing regular old eclipse glasses. It is safe, however, to put eclipse glasses over your everyday prescription eyewear.
And if you never got around to buying the right sort of protective eclipse glasses, you can still safely "watch" the event projected on a wall or the ground, NASA reminds us, with the help of an index card, a bit of aluminum foil and some tape.
Because of the way the light exposure damages cells of the retina, says Chou, a person who has suffered eye damage typically does not realize that there's any problem for hours after the eclipse.
Experience from past eclipses suggests that it's been younger people who seem more likely to ignore safety warnings, says Chou.
"It does tend to be young males," he says. "Teens to early 20s — the ones who don't think about any protection for a number of different circumstances."
But don't be so stressed out about eye safety that you miss the dramatic event known as totality. If you're lucky enough to be in the thin stretch of land across the country that's going to see a total solar eclipse, it's absolutely OK to look up with your naked eyes during the couple of minutes or so when the moon is completely covering the sun. In fact, it's more than OK.
"It is spectacularly beautiful and there's nothing else like it," says Rick Fienberg, press officer for the American Astronomical Society, who has seen a dozen total solar eclipses. "It's kind of like falling in love. You can't describe what that is unless you've experienced it."
When the sun completely blinks out, the safety glasses can come off so that you can enjoy the view of the sun's otherworldly corona and the eerie daytime darkness. But the instant a sliver of sun starts to re-emerge, he says, those glasses need to go back on if you want to keep watching.
"Going through life without seeing a total eclipse of the sun would be like going through life without ever falling in love," says Fienberg. "It would be a terrible shame not to have that fundamental, wonderful experience."