Mouse scratching ear until it bleeds- what do i do?

[moose]

i have an awesome little grey and white mouse i've had nearly a year. this mouse is absolutley spoiled and has a very intricate "critter trail". i only feed him the best natural mix they sell at my petstore and he regulary exercises in his ball.

i recently noticed that he has developed scabs on the back of his ear from constantly scratching. one of his eyes now appears a little puffy and i am now concerned there is a more complex problem than just the scratching of the ear. if somebody knows what is happening or has any advice of what action i should take, i would greatly appreciate it.

I also have a cat- is it possible Moose (my mouse) is allergic to the cat?