Movements may be horizontal, vertical, oblique, rotary, circular, or any combination of these. The defect is classified according to the position of the eyes when it occurs. The cause of nystagmus is unknown.
Reduced acuity is caused by the inability to maintain steady fixation.
Head nodding often accompanies congenital nystagmus. Nystagmus may be induced with an optokinetic drum or through the stimulation of the semicircular canals. With the exception of brief experiences of oscillopsia, most individuals with nystagmus perceive objects as being stationary. It is believed that the brain is responsible for the perceptual adjustment. As children with nystagmus mature, they seem to need these support devices less often.