like what IsabellaRobyn said - It's normal if it's just a little hard piece, (though you may find it before it hardens). It's like what humans get. Usually bunnies groom it off themselves eventually. When I had two bunnies, they would clean it off each other. It's the way eyes keep themselves moist during sleep I think and prevents tears from escaping out, (via this oil secretion) and then it catch dust, etc and begins to wash away as we wake up and "blink". They can turn hard, and if they don't come off easy from your bunny, you can get a damp warm cloth and gently wipe them away.
If the goobers in the eye though are excessive then that's when it can indicate something else. But it sound normal at this point.