Tens of millions of Americans will have spent the day staring at a total solar eclipse, and at least a few of them may become worried that they inadvertently damaged their eyes.

But experts say there's no need to panic — the vast majority of eclipse viewers are probably fine. And even if somebody did strain their eyes, the effects could be temporary.

During the 2017 total solar eclipse it's estimated that 150 million Americans viewed the event. There were around 100 documented cases of eye damage across all of America and Canada, according to Ralph Chou, an expert on eclipse eye safety with the University of Waterloo in Canada.

Far more people turned up in emergency rooms worried that they'd damaged their eyes. Many complained of watery eyes or blurred vision, but in most cases they were fine, according to Avnish Deobhakta, an ophthalmologist at the New York Eye and Ear Infirmary of Mount Sinai, one of the largest eye hospitals in the nation.

The reason it's hard to do real damage is simple — the human eye has evolved to avoid staring directly at the sun.

"It's so bright that we're not actually capable of looking at it without either tearing or sort of not really feeling comfortable staring at this ball of light," Deobhakta says.

In the rare case that someone does damage their eyes, that damage usually shows up as a blurry spot in the field of vision, hours or up to a day after watching the eclipse. In about half of cases, the problem fixes itself, but permanent damage can sometimes occur.

Anticipating the post-eclipse ocular anxiety, at least one eye clinic in Buffalo, N.Y., is offering free eye checks immediately after the eclipse on April 8.

It's always a good idea to get your eyes checked, whether or not there's an eclipse. So if you're worried at all, go ahead and use the opportunity to schedule your annual exam.

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