Due to its popularity (sometimes all 3 will force their way into one ball) I bought one ball for each hamster. Wear and tear sets in rapidly - what used to be clear plastic is now scratched and blurry. Poor hamsters will not be able to see the world clearly but then again I read that hamsters have very poor eyesight. However, I observed that the trouble is only with not being able to see food that they've dropped at their feet. When I call Mimi (she is the only one who responds to her name) from a distance, she will turn to look at me and come bouncing (rolling to be precise) to my feet. All pet lovers will understand that feeling of deep pleasure when their pets come bouncing/rolling when they call. It's worth all the crap picking and piss wiping.