By now, we all know how devastating hits to the head can be for NFL players. They've been known to cause concussions and memory loss and have had long-term effects on some former stars. But, did you know that they can also cause blindness?

During an interview on the NFL Network yesterday, 49ers wide receiver Michael Crabtree revealed that he took a hit from Ravens cornerback Jimmy Smith at the end of the Super Bowl last month that was so devastating that he temporarily lost his sense of sight.

"When the guy hit me, he hit me all in the face," Crabtree said. "I'm not tripping. I'm not one to whine about nothing, but he hit me all in the face and I couldn't really see after he hit me…Then [my vision] just came back. It's not concussion-like. When you get hit in football, it's going to feel like you can't see. It's going to feel intense. But, it snapped back. It happens all the time in football."

All the time? Then, why haven't we heard about it happening more often? Crabtree revealed that, after awhile, his vision came back. But, we have to believe that any hit that causes you to go blind can't be good for you. 

RELATED: The 50 Most Brutal Hits in NFL History

[via ESPN]