is rapid involuntary rhythmic
Eye Movement , with the eyes moving quickly in one direction (quick phase), and then slowly in the other (slow phase). The direction of nystagmus is defined by the direction of its quick phase (''e.g.'', ''right nystagmus'' is due to a right moving quick phase). Nystagmus may occur in the vertical or horizontal directions, and also in a semicircular movement, and thus are called downbeat nystagmus, upbeat nystagmus, seesaw nystagmus, periodic alternating nystagmus, and pendular nystagmus. There are other similar alterations in periodic eye movements (saccadic oscillations) such as
Opsoclonus or
Ocular Flutter . One can accurately think of nystagmus as the combination of a slow adjusting eye movement (slow phase) like would be seen with the
Vestibulo-ocular Reflex , followed by a quick
Saccade (quick phase) when the eye has reached the limit of its rotation.
In and the
Vestibular Apparatus (which controls
Posture and
Balance ). This may be
Physiological (or normal) or
Pathological .
An easy way of inducing physiological nystagmus is by having the person close her or his eyes and spin around. After a few spins, there is a distinct jerking of the eyes from side to side when they are reopened: this is . The degree of physiological nystagmus varies greatly between people and even in the same person at different times.
Another type of physiological nystagmus is the . It can be induced by presenting a moving pattern. The eyes tend to track the pattern, but snap back regularly. Nystagmus is distinguished from normal involuntary eye activity by the rapidity and repetitive pattern of the movement.
Nystagmus is a relatively common clinical condition, affecting one in every 5,000 to 10,000 individuals.
The cause for pathological nystagmus may be
Congenital ,
Idiopathic , secondary to a pre-existing
Neurological Disorder or may be induced temporarily by certain
Drug s (
Alcohol and other
Central Nervous System depressants and stimulants, such as
Lithium Salts ,
Dilantin and
Ecstasy ). Nystagmus generally causes a degree of
Vision Impairment , although the severity of such impairment varies widely.
If the pathologic nystagmus is based in the
Central Nervous System (CNS), such as with a
Cerebellar problem, the nystagmus will be in any direction ''including'' horizontal.
is always horizontal, and may be ''spontaneous'' or ''positional''.
is nystagmus that occurs spontaneously, regardless of the position of the patient's head.
In milder cases, the patient is often asked to fixate on an object, or wear
Fresnel Lens Glasses , which blur vision, to bring out the nystagmus.
is the opposite of spontaneous nystagmus in that it occurs when the patient's head is in a specific position (''e.g.'',
Benign Paroxysmal Positional Vertigo ; BPPV).
Again, in milder cases the patient is often asked to fixate on an object, or wear fresnel lens glasses, which blur vision, to bring out the nystagmus.
Horizontal nystagmus is also classified into three ''degrees'' as follows:
- ''First degree nystagmus'' is present only on lateral gaze, and has the fast phase in the direction of gaze;
- ''Second degree nystagmus'' is present in the primary (neutral) position of gaze;
- ''Third degree nystagmus'' is present in the same direction in all gaze positions
Such distinctions help to identify the anatomical source of the nystagmus. First degree nystagmus usually originates in the brainstem or cerebellum, while second and third degree nystagmus are usually vestibular in origin.
Other (extremely) rare pathologic nystagmuses are gaze paretic, rebound, fixation, congenital and dissociated nystagmus.
Some of the diseases which present nystagmus as a pathological sign are:
Congenital nystagmus occurs more frequently than acquired nystagmus, is not associated with other disorders (such as
Refraction Error s or
Diplopia ) and is usually mild and non-progressive. The affected persons are not aware of their spontaneous, small-amplitude eye movements.
- Congenital
- Infantile:
- Idiopathic
- Albinism
- Aniridia
- Leber's Congenital Amaurosis
- Bilateral optic nerve hypoplasia
- Bilateral congenital cataracts
- Rod Monochromatism
- Optic nerve or macular disease
- Persistent hyperplastic primary vitreous
- Latent nystagmus
- Nystagmus blockage syndrome
- Acquired
- Visual Loss (e.g. dense Cataract , Trauma , cone dystrophy)
- Toxic/metabolic (e.g. alcohol intoxication, lithium, barbituates, phenytoin(Dilantin), salicylates, benzodiazepines, phencyclidine, other anticonvulsants or sedatives, Wernicke's Encephalopathy , Thiamine deficiency)
- Central nervous system disorders (e.g. thalamic hemorrhage, Tumor , Stroke , trauma, Multiple Sclerosis )
- Non-physiologic
Nystagmus can be clinically investigated by using a number of
Non-invasive standard tests. The simplest one is to irrigate an
External Auditory Meatus with warm or cold water. The temperature gradient provokes the stimulation of the
Vestibulocochlear Nerve and the consequent nystagmus.
The resulting movement of the eyes may be recorded and quantified by a special device called
Electronystagmograph (ENG), which is a form of
Electrooculography (an electrical method of measuring eye movements using external
Electrodes ). Special swinging chairs with electrical controls are also used in this test to induce rotatory nystagmus.
Pathological acquired nystagmus is mostly a temporary condition and stops spontaneously. When it is secondary to a neurological disorder, this must be treated accordingly. Congenital nystagmus is usually non-treatable, but several therapeutic approaches, such as
Contact Lenses , drugs,
Surgery , and
Low Vision Rehabilitation can be used in order to improve visual function.
