And then Trump looked at the sun without glasses. And everybody is throwing fits about what an idiot he is. I commented on one article that no, it's not likely you'll go blind if you just glance at the sun for a second*, and one person replied "but this isn't the sun, it's the eclipse!" like that's a winning argument. I mentioned to another, who claimed you couldn't see anything without the glasses until totality anyway that I'd been staring at the cloud cover impatiently before the peak, and when the clouds parted I'd gotten an unprotected glimpse of the sun and yes, I could see the bite of it - and that person went "Well, you do permanent damage at 20 seconds, so you might've been lucky". How long do they imagine it takes to see the sun when the clouds break and then look down again?
I think I've figured this out.
The rule is "You should not stare at the sun, even during an eclipse". This is a sensible rule that nobody has ever needed to tell anybody over the age of, say, six weeks. We don't stare at the sun. Even infants know better - if the sun shines in your eyes, you squint, put your hand up, and turn away. Aniamls are even smarter! No matter what happens, they don't need to be told.
But humans think we're cleverer than animals, and during an eclipse we sometimes break that rule and look at the sun because it's cool. And because the light seems dimmer, we can look longer. But it's not really dimmer - it's just as bright, it's just that some of it is blocked. So for the past year, we've had it drummed into our heads that you shouldn't look at the eclipse without glasses. Consequently, many people have internalized the rule as "You shouldn't stare at the sun, especially during an eclipse". But the sun isn't any more dangerous then. It's only our behavior that changes!
If you look for up to five seconds, you're probably fine, just like when you turn a corner and find yourself driving toward the sun. (Or look up at a flock of birds just as the clouds part and find the sun glaring in your eyes, or wake up with the sun in your eyes.) According to the only study on the subject, you're not likely to have visible damage unless you look for 15 seconds or longer... and even then, most patients improved with time.
So don't stare at the sun, but if you did catch a glimpse, whether on purpose or not, it's probably no more harmful than when you catch a glimpse of the sun on regular days.
(As for Trump, this was a dumb move, but not because of the potential eye damage. It was a dumb move because everybody and their dog, literally, knows better but he still did it on national TV. Doofus. And if he's getting any flak from it he probably blames the aide for calling attention to his behavior rather than his own foolish decision to do something everybody knows, from the very day they're born, not to do.)
* Turns out it was more like 30 seconds in his case, which is really way too long. Not that I give a fuck what that person does to his eyes.