When I was about 10 years old, my younger sister and I were watching "Escape to Witch Mountain" on Disney. Some harmless horseplay during one of the commercials... then... she sliced one of my eyes open with her fingernail. (Yes, it is all fun and games until someone takes a fingernail to the eye.
)
Fortunately, it was a surface cut, towards the outer edge of my eye; I didn't lose any sight. The Emergency Room filled my eye with glue-like-goo to keep my eye shut (blinking would only open the cut further - EEK), and a bright white patch for 2 weeks. That resulted in other minor injuries since my depth perception was poor, but nothing as serious as the original eye injury.