That’s something analogous to a bruise or a blood blister on my eyeball, from a piece of grit getting thrown into my eye at high speed. Whee! It hurt right when it happened, but almost immediately felt completely fine (and still feels fine now several hours later). If it had been a couple millimeters over, though, that might have been a very different story.
Don’t try this at home, kids! Wear eye protection!
PS — And of course after this happened (and I’d taken a look and satisfied myself that the damage wasn’t too serious), I went and found the safety goggles I’d been too lazy to look for before starting.