When doing a roll, pick a focal point to represent your attacker and keep your eyes on that as you do your roll. At some point in the roll your eyes may have to leave that focal point for a second or two, but return your gaze to that spot. This is what skaters or dancers do when doing turns and spins. When you think about it, it makes sense to train in this way because you don't want to do a roll without purpose. It is in relation to your attacker. Your body will get accustomed to rolling and not be as sensitive to it the longer you train also. I believe your sensei wanted you to just keep doing them so you can figure this out for yourself.