I did that, once...
...in a squash court...
...I only hit the ball gently...
...and I saw it clearly, about 30cm in front of my eyeball...
..ooO( "This was a bad idea!" ), I thought...
...and then I was flat on my back and I couldn't see anything.

Don't try this, anywhere.
( Bee Nice General disorders > Death and Sudden Death > Death, Fri 8 Feb 2008, 14:38, archived)