i've had some suspicion and done a number of tests at home..he has no response to sound. seems from what i hear it is not a huge deal in ferrets as they compensate, live healthily, and don't even seem to realize their handicap. i'm not going to depend on medical testing as i've heard there are numerous tests that are painful that aren't really necessary. just need to be more aware of how i communicate with him and definitely not depend on voice cues for discipline. otherwise, he is a very happy guy and i'm sure he doesn't mind not hearing the dogs go crazy barking in the middle of the night
a lot of people may not realize their ferret is deaf and get frustrated that he/she is not listening to voice cues which can result in frustration and poor care or even abandonment or abuse. i'm just glad i've stumbled upon this early on...