is a type of eye movement characterized by alternating slow phase movements in one direction and Saccade
-like quick phases in the other direction. There are two types of nystagmus:
- Physiologic nystagmus when occurring normally and serving its normal function. In this case the slow phases are vestibulo-ocular reflex movements that stabilize vision during head movement, whereas the fast phases are re-setting movements.
- Pathologic nystagmus when occurring abnormally. In this case the slow phases may be due to a vestibular imbalance or due to failure in the eye position-holding mechanisms of the oculomotor system.