Hi Debra .....
It is rather common to do balance testing during the diagnosing phase ..... but I'm puzzled by the reason being to tell how off balance you will be after surgery.
Yes, the tests will give some degree of knowledge as to how your vestibular nerves are functioning (or not functioning) now, but I've never heard that used to determine how you will be post-op. I am not a doctor so just curious here.
Perhaps he is saying that if the tests show poor to no functioning of your vestibular nerve now (on your AN side) ..... and if you are having no particular balance issues right now, that is an indicator that your brain has probably already compensated by shifting the balance job over to your good vestibular nerve ..... and you would have less balance issues post-op when they remove the damaged vestibular nerve. If the AN has not particularly affected the function of the vestibular nerve to this point, then you potentially will have considerably more balance issues post-op.
Just my thoughts .....
Clarice