Hi Claire,
I do not have rotary nystagmus, but I do have mild positional nystagmus, which is beating of the eyes when I lie on my right side. These eye movements are caused by the neuroma affecting the balance nerve. The balance nerve is also called the vestibular nerve, and in fact most acoustic neuromas start on the vestibular nerve. That is why the radiologists always refer to them as vestibular schwannomas.
Unfortunately, the doctors really don't know why some people get it and some don't, or whether your GK treatment will help that symptom. You will have to wait and see. Does the rotation movement cause you very much difficulty? Does it happen all the time, or just now and then?
Anyway, it is good to hear that you have arranged for treatment of your AN. The most important thing is to prevent more problems from developing. If you get a chance, you can put the date on the AN calendar (see the bottom of this post), so we can all wish you well when your treatment date arrives.
Take care,
Steve