Which is nystagmus and what causes the eyes to move rapidly?

Can be both: Nystagmus can be congenital or acquired. Congenital form can associate with an underlying hereditary eye disease or by itself alone. Acquired form can be from certain medications, diseases that affect the eye sight or neurologic conditions. Congenital forms occur from day one after birth, while acquired forms can happen any time during life time. Any nystagmus should be evaluated.