Nystagmus is usually caused by diseases affecting the cerebellum. It is the part of the brain that maintains balance.
Damage to the brain from disease or trauma may cause nystagmus. The brainstem and the cranial nerves can also cause nystagmus if affected by disease or trauma. The cranial nerves control eye movement and their nerve fibers as those of the cerebellum pass through the brainstem. The brainstem connects the brain to the spinal cord.