Nystagmus is an uncontrollable (involuntary), rapid, rhythmic movement of the eyes. The frequency and direction of eye movements may help determine underlying conditions such as brain stem tumors, abnormalities in visual perception, neural (nervous system) disorders, or drug-induced reactions.
Involuntary eye movement may be from side-to-side, up-and-down, or in a circular motion. About 45 different types of nystagmus have been identified. Some eye movements may appear to undulate at the same speed (pendular) or they may move slowly in one direction and then jerk back to the original position. Many people with nystagmus have a "null point," an angle of gaze where eye movement is reduced and vision improved. In some cases, the position of the null point causes the individual to have a head tilt (anomalous head posture or AHP).
Nystagmus may appear in early childhood or infancy (congenital nystagmus) or later in life (acquired nystagmus). Acquired nystagmus may be a symptom of another medical condition such as stroke, multiple sclerosis, brain tumor, meningitis, or head injury. Nystagmus can also be caused by chemical agents such as barbiturates or other sedatives, anticonvulsants, and alcohol. Nystagmus is neither infectious nor contagious.Risk: Most nystagmus that begins in childhood is linked to eye disease and vision loss, often resulting from heredity (genetics). Other forms of nystagmus that begin later in life may be associated with conditions such as brain tumors, multiple sclerosis, or tumors. Incidence and Prevalence: Studies indicate the prevalence of nystagmus among children as being 0.1% (Windsor). Nystagmus that develops after early childhood (acquired nystagmus) may be linked to any number of underlying conditions, and incidence is unknown. |
Source: Medical Disability Advisor
History: Nystagmus can be an inherited condition, but in many cases there is no family history of the disorder. Any initial presentation of nystagmus after 6 years of age should be considered acquired nystagmus and secondary to another condition. Individuals with acquired nystagmus usually report recent onset of signs and symptoms such as the perception that stationary objects are moving (oscillopsia), dizziness, or ringing in the ears (tinnitus). Physical exam: Characteristic rapid eye movements and tilting of the head (AHP) may be observed. Visual acuity decreases and the visual field diminishes. Individuals may be seeing double images (diplopia), or have hearing loss associated with a disorder of balance and orientation (vestibular system). Tests: Several tests are used to diagnose or rule out different types of nystagmus. An individual may be instructed to look in various directions upon command (command movements) to test eye movement and fixation. The individual may be asked to hold the head still while using the eyes to follow a moving target (pursuit system tests). In an optokinetic nystagmus or OKN test, the individual holds the head still while watching targets move simultaneously in different directions. OKN testing helps diagnose congenital nystagmus and can indicate whether ordinary ocular movements are intact.
Other eye movement tests (electronystagmography or ENG) are directed at finding possible balance and orientation (vestibular system) abnormalities or neural dysfunction. "Doll's head test" or oculocephalic maneuver partly involves having the patient move the head in one direction while the eyes rotate in the opposite direction. This test assesses whether the part of the brainstem involved in transmitting eye movements is still functioning. Caloric testing is used on the vestibular system and evaluates how eyes react when warm water or ice water is poured into one ear at a time. Neuroimaging testing is done (MRI or CT) to determine if acquired nystagmus might involve a major nerve (eighth cranial nerve) or its brainstem pathways affecting balance. If drug toxicity is suspected, medication blood levels and testing for illegal drug use may be indicated. |
Source: Medical Disability Advisor
There is no cure for nystagmus itself, but treatment may be directed at the underlying cause. For example, brainstem tumors may require surgery. Nystagmus caused by drug toxicity may resolve when medication dose is reduced or the drug discontinued. Treatments including corrective lenses, prisms or surgery can help improve visual acuity, improve the appearance of the individual, and/or reduce nystagmus.
Because contact lenses move with the eyes, they allow the eye to focus through the optical center of the lens at all times and are therefore more effective than glasses at correcting vision if a null point exists. Sensation accompanying small movements of the contact lenses on the eye has been shown in some studies to help reduce nystagmus.
Prisms may be used when an individual has problems with work or driving. In these cases, the prisms eliminate AHP and improve visual acuity. The prisms are generally placed with the apex toward the null point of each eye, thus moving the eyes into the primary position. The use of prisms is limited to individuals with effective vision in both eyes (binocular vision). Disadvantages of prisms include increased weight of prism glasses and awkward appearance.
Surgery can correct AHP by directing the eyes toward the head shift. This shifts the null point into the straight-ahead position. The surgery involves lengthening and weakening the four horizontal muscles around the eye. Another surgical procedure shortens the outer horizontal muscle (lateral recti) of the eye in order to induce convergence, which dampens the nystagmus. This procedure can only be performed on individuals with binocular vision. Complications of surgery include overcorrection of the AHP, double vision, and difficulty moving the eyes in certain directions.
A newer therapy involves injection of a poisonous substance (botulinum toxin) into certain muscles responsible for rotating the eye to minimize abnormal movements associated with nystagmus. Results are short-term, and complications associated with this treatment include adverse effects on other eye movements and possible development of double vision (diplopia) or drooping eyelids (ptosis). |
Source: Medical Disability Advisor
| Congenital nystagmus tends to persist throughout an individual's life, whereas nystagmus that develops from conditions such as viral infection of the inner ear (viral labyrinthitis) or drug toxicity usually resolves along with the underlying problem. Nystagmus generally is not painful and does not lead to total blindness. Quality of life may be affected by persistent reduction in depth perception, decreased reading speed, and periods of sensation that stationary objects are moving (oscillopsia). Most individuals with nystagmus are capable of leading productive, independent lives. |
Source: Medical Disability Advisor
| Because nystagmus is typically a persistent condition, traditional rehabilitation is not usually indicated. Exercise therapy is not generally beneficial for nystagmus, but localization exercises can be helpful if another eye disorder such as strabismus is also present. |
Source: Medical Disability Advisor
| The inability to hold a steady gaze almost always results in some loss of visual acuity. The perception that stationary objects are moving (oscillopsia) and the loss of depth perception can cause individuals with nystagmus to lose their balance or appear clumsy. Nystagmus that comes on suddenly such as with a viral infection of the inner ear (viral labyrinthitis) is often associated with nausea and vomiting. |
Source: Medical Disability Advisor
| Individuals with nystagmus may not be able to obtain a driver's license. Those with a constant head tilt may experience physical discomfort or neck pain, and seating position accommodations should be made to provide the individual with the best angle of vision when looking at blackboards or screens. The option of large print material should be made available. Computer screens should be adjusted for brightness, character size, and angle. Most individuals with nystagmus benefit from good task lighting. When balance problems accompany nystagmus, working at heights or under conditions that require agility and stability should be avoided. |
Source: Medical Disability Advisor
| If an individual fails to recover within the expected maximum duration period, the reader may wish to consider the following questions to better understand the specifics of an individual's medical case. Regarding diagnosis:
- Does individual have congenital or acquired nystagmus?
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Has individual had a stroke or brain tumor?
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Does individual have multiple sclerosis, meningitis, or head injury?
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Does individual use barbiturates, sedatives, anticonvulsants or alcohol?
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How old was individual at onset of nystagmus?
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What underlying condition causes nystagmus?
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Does individual report that stationary objects appear to be moving?
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Does individual have dizziness or ringing in the ears?
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Does individual have a head tilt or reduced visual acuity?
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Has individual had command movements, pursuit system tests and optokinetic nystagmus testing done?
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Have conditions with similar symptoms been ruled out?
Regarding treatment:
- Has individual had treatment for the underlying cause?
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Has individual had a complete vision examination?
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Is individual a candidate for contact lenses or prisms?
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Is individual a surgical candidate?
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Has individual considered a botulinum toxin injection?
Regarding prognosis:
- Is individual's employer able to accommodate any necessary restrictions?
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Does individual have any conditions that may affect ability to recover?
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Does individual easily lose balance or appear clumsy?
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Does individual understand the effect that tiredness, stress, tension, nervousness or unfamiliar surroundings can have on visual acuity?
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Source: Medical Disability Advisor
| CitedWindsor, Richard L., and Laura K. Windsor. "Nystagmus." The Low Vision Gateway. Internet Low Vision Society. 20 Oct. 2004 <http://lowvision.org/nystagmus.htm>. |
Source: Medical Disability Advisor