"Spin" the eyes

No, they don't spin all the way around, but they can spin enough to make a person sense that kind of eye movement as spinning.  This abnormal eye movement is called nystagmus.  With nystagmus, there is a quick beat in one direction and a slow beat in the opposite direction.  Naming the nystagmus and looking for patterns with and without the ability to focus is key in figuring out why the nystagmus is present.