Nystagmus is not to be confused with other superficially similar-appearing disorders of eye movements (saccadic oscillations) such as opsoclonus or ocular flutter that are composed purely of fast-phase (saccadic) eye movements, while nystagmus is characterized by the combination of a smooth pursuit, which usually acts to take the eye off the point of focus, interspersed with the saccadic movement that serves to bring the eye back on target. Without the use of objective recording techniques, it may be very difficult to distinguish among these conditions. In medicine, the presence of nystagmus can be benign, or it can indicate an underlying visual or neurological problem. Pathologic nystagmus
Pathological nystagmus is characterized by "excessive drifts of stationary retinal images that degrades vision and may produce illusory motion of the seen world: oscillopsia (an exception is congenital nystagmus)".When nystagmus occurs without fulfilling its normal function, it is pathologic (deviating from the healthy or normal condition). Pathological nystagmus is the result of damage to one or more components of the vestibular system, including the semicircular canals, otolith organs, and the vestibulocerebellum.Pathological nystagmus generally causes a degree of vision impairment, although the severity of such impairment varies widely. Also, many blind people have nystagmus, which is one reason that some wear dark glasses. Variations
Central nystagmus occurs as a result of either normal or abnormal processes not related to the vestibular organ. For example, lesions of the midbrain or cerebellum can result in up- and down-beat nystagmus.
Gaze induced nystagmus occurs or is exacerbated as a result of changing ones gaze toward or away from a particular side which has an affected central apparatus. Peripheral nystagmus occurs as a result of either normal or diseased functional states of the vestibular system and may combine a rotational component with vertical or horizontal eye movements and may be spontaneous, positional, or evoked. Positional nystagmus occurs when a persons head is in a specific position. An example of disease state in which this occurs is Benign paroxysmal positional vertigo (BPPV). Post rotational nystagmus occurs after an imbalance is created between a normal side and a diseased side by stimulation of the vestibular system by rapid shaking or rotation of the head. Spontaneous nystagmus is nystagmus that occurs randomly, regardless of the position of the patients head. Physiological nystagmus
Physiological nystagmus is a form of involuntary eye movement that is part of the vestibulo-ocular reflex (VOR), characterized by alternating smooth pursuit in one direction and saccadic movement in the other direction. Variations
The direction of nystagmus is defined by the direction of its quick phase (e.g. a right-beating nystagmus is characterized by a rightward-moving quick phase, and a left-beating nystagmus by a leftward-moving quick phase). The oscillations may occur in the vertical, horizontal or torsional planes, or in any combination. The resulting nystagmus is often named as a gross description of the movement, e.g. downbeat nystagmus, upbeat nystagmus, seesaw nystagmus, periodic alternating nystagmus.