Nystagmus (redirected from Nystagmus, optokinetic)

Nystagmus 

Definition

Rhythmic, oscillating motions of the eyes are called nystagmus. The to-and-fro motion is generally involuntary. Vertical nystagmus occurs much less frequently than horizontal nystagmus and is often, but not necessarily, a sign of serious brain damage. Nystagmus can be a normal physiological response or a result of a pathologic problem.

Description

The eyes play a critical role in maintaining balance. They are directly connected to other organs of equilibrium, most important of which is the inner ear. Paired structures called the semicircular canals deep in the skull behind the ears sense motion and relay that information to balance control centers in the brain. The eyes send visual information to the same centers. A third set of sensors consists of nerve endings all over the body, particularly in joints, that detect position. All this information is integrated to allow the body to navigate in space and gravity.

It is possible to fool this system or to overload it with information so that it malfunctions. A spinning ride at the amusement park is a good way to overload it with information. The system has adapted to the spinning, expects it to go on forever, and carries that momentum for some time after it is over. Nystagmus is the lingering adjustment of the eyes to tracking the world as it revolves around them.

Nystagmus can be classified depending upon the type of motion of the eyes. In pendular nystagmus the speed of motion of the eyes is the same in both directions. In jerk nystagmus there is a slow and fast phase. The eyes move slowly in one direction and then seem to jerk back in the other direction.

Nystagmus can be present at birth (congenital) or acquired later on in life. A certain type of acquired nystagmus, called spasmus nutans, includes a head tilt and head bobbing and generally occurs between four to 12 months of age. It may last a few months to a few years, but generally goes away by itself.

Railway nystagmus is a physiological type of nystagmus. It happens when someone is on a moving train (thus the term railway) and is watching a stationary object which appears to be going by. The eyes slowly follow the object and then quickly jerk back to start over. Railway nystagmus (also called optokinetic nystagmus) is a type of jerk nystagmus. This phenomenon can be used to check vision in infants. Nystagmus can also be induced by fooling the semicircular canals. Caloric stimulation refers to a medical method of testing their connections to the brain, and therefore to the eyes. Cold or warm water flushed into the ear canal will generate motion signals from the inner ear. The eyes will respond to this signal with nystagmus if the pathways are intact.

Causes and symptoms

There are many causes of nystagmus. Nystagmus may be present at birth. It may be a result of the lack of development of normal binocular fixation early on in life. This can occur if there is a cataract at birth or a problem is some other part of the visual system. Some other conditions that nystagmus may be associated with include:

Diagnosis

Nystagmus is a sign, not a disease. If abnormal, it indicates a problem in one of the systems controlling it. An ophthalmologist and/or neuro-ophthalmologist should be consulted.

Treatment

There is one kind of nystagmus that seems to occur harmlessly by itself. The condition, benign positional vertigo, produces vertigo and nystagmus when the head is moved in certain directions. It can arise spontaneously or after a concussion. Motion sickness medicines sometimes help. But the reaction will dissipate if continuously evoked. Each morning a patient is asked to produce the symptom by moving his or her head around until it no longer happens. This prevents it from returning for several hours or the entire day.

Prisms, contact lenses, eyeglasses, or eye muscle surgery are some possible treatments. These therapies may reduce the nystagmus but may not alleviate it. Again, because nystagmus may be a symptom, it is important to determine the cause.

Resources

Organizations

American Academy of Ophthalmology. 655 Beach Street, P.O. Box 7424, San Francisco, CA 94120-7424. http://www.eyenet.org.

American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. http://www.aoanet.org.

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nystagmus /nys·tag·mus/ (nis-tag´mus) involuntary rapid movement (horizontal, vertical, rotatory, or mixed, i.e., of two types) of the eyeball.nystag´mic

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aural nystagmus  vestibular n.

caloric nystagmus  rotatory nystagmus induced by irrigating the ears with warm or cold water or air; see caloric test, under test.

Cheyne's nystagmus , Cheyne-Stokes nystagmus a peculiar rhythmical eye movement.

dissociated nystagmus  that in which the movements in the two eyes are dissimilar.

end-position nystagmus  that occurring in normal individuals only at extremes of gaze.

fixation nystagmus  that occurring only on gazing fixedly at an object.

gaze nystagmus  nystagmus made apparent by looking to the right or to the left.

gaze paretic nystagmus  a form of gaze nystagmus seen in patients recovering from central nervous system lesions; the eyes fail to stay fixed to the affected side with a cerebral or pontine lesion.

labyrinthine nystagmus  vestibular n.

latent nystagmus  that occurring only when one eye is covered.

lateral nystagmus  involuntary horizontal movement of the eyes.

opticokinetic nystagmus , optokinetic nystagmus the normal nystagmus occurring when looking at objects passing across the field of vision, as in viewing from a moving vehicle.

pendular nystagmus  that which consists of to-and-fro movements of equal velocity.

positional nystagmus  that which occurs, or is altered in form or intensity, on assumption of certain positions of the head.

retraction nystagmus , nystagmus retracto´rius a spasmodic backward movement of the eyeball occurring on attempts to move the eye; a sign of midbrain disease.

rotatory nystagmus  involuntary rotation of eyes about the visual axis.

spontaneous nystagmus  that occurring without specific stimulation of the vestibular system.

undulatory nystagmus  pendular n.

vertical nystagmus  involuntary up-and-down movement of the eyes.

vestibular nystagmus  that due to disturbance of the vestibular system; eye movements are rhythmic, with slow and fast components.

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nys·tag·mus (n-stgms)

n.

A rapid, involuntary oscillatory motion of the eyeball.

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nys·tagmic (-mk), nys·tagmoid (-moid) adj.

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nystagmus (nis·tagˑ·ms),

n a rapid, involuntary movement of the eyes that typically occurs as a result of vertigo throughout and following the rotation of the body or following injuries to the vestibule of the ear or the cerebellum. Also called
nystaxis.

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nystagmus (nīstag´mus),

n the state of oscillatory movements of an organ or part, especially the eyeballs; irregular jerking movement of the eyes. Each movement of the cycle consists of a slow component in one direction and a rapid component in the opposite direction.

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nystagmus

a periodic, rhythmic, involuntary movement of both eyeballs in unison. There is a slow component in one direction and a quick return. The movement may be vertical, horizontal or rotary. Common causes are lesions of the cerebellum or the vestibular apparatus, or increased intracranial pressure.

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aural nystagmus

labyrinthine nystagmus.

cerebellar nystagmus

one characterized by tremor, without fast and slow components.

Cheyne's nystagmus

a peculiar rhythmical eye movement resembling Cheyne-Stokes respiration in rhythm.

congenital nystagmus

may be a primary functional defect or secondary to lesions in the visual pathways, sometimes associated with albinism. Reported in cattle, cats (particularly Siamese), and dogs.

dissociated nystagmus

that in which the movements in the two eyes are dissimilar.

gaze nystagmus

nystagmus made apparent by looking to the right or to the left.

horizontal nystagmus

that in which the eyes move from side to side with the fast component opposite to the side of the lesion; seen with central or unilateral peripheral vestibular disease.

jerk nystagmus

vestibular nystagmus (see below).

labyrinthine nystagmus

vestibular nystagmus due to labyrinthine disturbance.

latent nystagmus

that occurring only when one eye is covered.

lateral nystagmus

involuntary horizontal movement of the eyes.

ocular nystagmus

wandering movement of the eyes as though searching for something. Associated with congenital blindness.

optokinetic nystagmus

nystagmus induced by looking at objects moving across the field of vision.

oscillatory nystagmus

pendular nystagmus.

pendular nystagmus

that which consists of to-and-fro movements of equal velocity.

positional nystagmus

that which occurs, or is altered in form or intensity, on assumption of certain positions of the head.

postrotatory nystagmus

a normal finding after the animal has been rotated, with the fast phase away from the direction of rotation.

resting nystagmus

that occurring while the head is stationary.

retraction nystagmus, nystagmus retractorius

a spasmodic backward movement of the eyeball occurring on attempts to move the eye; a sign of midbrain disease.

rotatory nystagmus

involuntary rotation of the eyes about the visual axis.

spontaneous nystagmus

that occurring without specific stimulation of the vestibular system.

vertical nystagmus

involuntary up-and-down movement of the eyes.

vestibular nystagmus

nystagmus due to disturbance of the labyrinth or of the vestibular nuclei; the movements are usually jerky.

undulatory nystagmus

an inherited disorder of Finnish Ayrshire cattle; there is a synchronous, tremor-like movement of the eyes but affected aninals are otherwise healthy.