Nystagmus
Definition
Nystagmus is a condition in which there is involuntary and rhythmic movement or oscillation of the eye. It is often caused by an underlying ocular or neurological disorder.
Description
The eye movements associated with nystagmus are varied. They can be either pendular, in which the oscillations are equal in all directions and or jerk, in which the movements may be faster in one direction than another. The frequency of the oscillation or movement and the amplitude of the oscillation also vary. The movements themselves may be vertical, horizontal, circular, or oblique in direction. Nystagmus can be sensory and develop as a result of poor vision, or it can be motor and develop as a result of a neurological problem.
Nystagmus may be congenital, or it may be acquired. Congenital, or infantile, nystagmus appears within the first few months of life. Congenital nystagmus is usually binocular and affects both eyes, is horizontal in direction, and does not occur while the child is sleeping. It decreases when the child's eyes converge or move inward. Most of these cases of nystagmus develop because of poor vision and do not have an underlying neurological cause.
Children with congenital nystagmus usually have a point in their eye movement in which the intensity of the nystagmus is decreased. This is called the null point, and the child may adopt a head tilt or rotation to help maintain his or her eyes at this position. This point is usually not in straight ahead or in a primary gaze position. Children with nystagmus who have their the null point located at a position in which the eyes are positioned inward may develop an esotropia, a form of strabismus or eye turn.
One variant of congenital nystagmus is spasmus nutans, which appears as a triad with accompanying head nodding and torticollis (head turn or tilt), and is seen between four months and three-and-a-half years of age and usually resolves without treatment within one to two years of onset. Rarely does it persist past age five. Usually spasmus nutans appears bilaterally, and the nystagmus is in a horizontal direction. When the nystagmus of spasmus nutans is vertical or rotary, the child does not have a head tilt.
There are various types of nystagmus. Downbeat nystagmus is characterized by a nystagmus that is more pronounced when the child looks down, especially when looking to the side, or in lateral gaze. An accentuated oscillation when looking up is seen in upbeat nystagmus. Seesaw nystagmus is an unusual type of in which one eye moves in and down and the other out and up. A periodic alternating nystagmus (PAN) is observed in primary gaze when the patient is looking straight ahead and is characterized by eye movements that continuously change direction and speed. Peripheral vestibular nystagmus may be accompanied by vertigo, nausea , and tinnitus, or ringing in the ears. This type of nystagmus is not always apparent but can be seen by a doctor when he or she looks in the back of the eye with a direct ophthalmoscope.
Latent nystagmus appears only when one eye is covered. This is a congenital nystagmus caused by an ocular motor disturbance rather than visual deprivation. It is often accompanied by strabismus or an eye turn. A child with latent nystagmus will not see well when one eye is covered.
Gaze evoked nystagmus occurs only when one is looking to the side in extreme lateral gaze. This type of nystagmus can be caused by ethanol and recreational drug use, but is seen in myasthenia gravis and thyroid disease as well.
Some types of nystagmus are normal. If one looks at an object in extreme gaze for a long period of time, endpoint nystagmus may be noted. Optokinetic nystagmus (OKN) is a nystagmus that can be elicited involuntarily when a rapidly moving striped object is passed in front of an individual's eyes.
Transmission
Congenital nystagmus may be transmitted genetically, either as an autosomal recessive or dominant, or as an X-linked recessive trait. It can also be associated with other conditions that are genetically transmitted. For example, Leber's amaurosis is an autosomal dominant trait and albinism is X-linked.
Demographics
Congenital nystagmus occurs twice as frequently in males than in females. The prevalence of nystagmus in the pediatric population is .015 percent. Eighty percent of nystagmus is congenital, and the remaining 20 percent is acquired.
Causes and symptoms
The eyes of an individual with nystagmus cannot remain still and oscillate in some position of gaze. Those with nystagmus usually have decreased vision and poor depth perception, although those born with nystagmus, may not realize that their vision is poor. Those with acquired nystagmus may experience double vision or oscillopsia, or that objects in their visual space appear to move. An acquired nystagmus may be accompanied by other symptoms such dizziness , difficulty with balance, hearing loss, poor coordination, and numbness . If an individual with nystagmus experiences oscillopsia, then the nystagmus is acquired.
The primary cause of congenital nystagmus is visual deprivation, and the causes of visual deprivation in an infant include cataracts, oculoalbinism, glaucoma, retinal detachments, Leber's amaurosis, developmental abnormalities of the optic nerve such as a coloboma, and achromatopsia, a condition in which the infant cannot see color.
Acquired nystagmus can be caused by demyelination of nerve fibers, such as occurs in multiple sclerosis, lesions or tumors of the vestibular or visual pathways, strokes of the central nervous system, and drug use, both recreational as well as a side effect of prescribed drugs, such as those used to treat seizures and depression. Other causes of acquired nystagmus are Arnold-Chiari malformations, vitamin deficiencies, syphilis, Wernicke's encephalopathy, Behcet's syndrome, and Meniere's disease.
When to call the doctor
Since nystagmus can be caused by tumors, stroke , and trauma or neurological disorder, any type of nystagmus must be evaluated by a qualified practitioner. The nystagmus can be a sign of a serious problem. For example, a type of tumor called chiasmal glioma has signs and symptoms similar to spasmus nutans.
Diagnosis
Diagnosis of nystagmus is made primarily by patient history as reported by a parent, the age of onset, and observation of any accompanying signs such as a head turn, tilt or tremor, or oscillopsia. If possible, the infant or child's best visual acuity is determined. If the onset is acute, then usually the nystagmus is acquired.
The type of nystagmus can accurately be determined by eye movement recordings, which map direction, frequency, null point, and amplitude of the nystagmus. For the infant with congenital nystagmus, evoked response potential (EVR) and electroretinogram (ERG) give the doctor objective information about visual potential, and magnetic resonance imaging (MRI) can determine if and where a lesion is located. For the infant or young child, some of these tests may be done under anesthesia.
Treatment
The treatment for nystagmus, once the etiology is determined and treated, includes optical devices such as contact lenses and glasses, medication, and surgery.
For individuals with nystagmus correction of refractive error with glasses or contact lenses is the first step in treating the condition. For 85 percent of children with nystagmus, a spectacle prescription improves vision significantly. For those with congenital nystagmus, prism may be put in glasses to help position the eye at its null point or to help the eyes converge. For some people contact lenses are prescribed. Contact lenses slow down eye movements, and because the optical center of the prescription is always centered on the eye with the contact lens, vision improves. Low vision aids such as telescopes assist those whose vision cannot be fully corrected with spectacles and contact lenses alone. Tinting of the glasses or sunglasses may decrease the nystagmus of individuals with albinism. For the patient with oscillopsia, grinding prism into the spectacles may move the visual field to a point of decreased oscillopsia.
Congenital nystagmus, when due to a visual deprivation, is rarely improved by surgery. But when a head tilt or head turn accompanies nystagmus, surgery to correct a muscle imbalance may improve nystagmus and visual acuity. Surgery on the extraocular muscles of the eye may be helpful when the child's null point is in not in primary gaze but located at least 30 degrees from straight-ahead vision. When a tumor or stroke has caused an acquired nystagmus, then neurosurgery, if indicated for the underlying cause, may lead to resolution of the nystagmus. When surgery is considered, the risks of anesthesia must also be considered.
If oscillopsia is a co-existing symptom, then drugs can be given to reduce the ocular oscillations. Vestibular nystagmus can be treated by diazepam or scopolamine. Drugs called GABA agonists, such as baclofen and carbamazepine, are useful in treatment of seesaw nystagmus and PAN, if the nystagmus is acquired and not congenital. Baclofen cannot be given to children.
Botox ( Botulinum toxin) injections can temporarily control the eye movements, but because of side effects such as double vision and ptosis or drooping of the eyelid, and because it is not a permanent solution, Botox is not used often.
If the nystagmus is due to drug toxicity, then reducing or discontinuing the drug eventually resolves the problem.
Alternative treatment
Acupuncture and biofeedback and vision therapy have been successful for some patients.
Prognosis
Congenital nystagmus is usually a benign condition. It is not curable, but its symptoms can be diminished with spectacles or contact lenses. The best corrected vision for most individuals with congenital nystagmus is between 20/40 and 20/70, but correction to 20/20 is possible for some. Nystagmus associated with spasmus nutans resolves spontaneously before the child reaches school age.
The prognosis for an acquired nystagmus depends on its cause. If the condition is due to a side effect of a drug, then decreasing or changing the treatment drug eventually resolves the nystagmus.
Prevention
In general nystagmus cannot be prevented. Since the cause of acquired nystagmus can be due to a co-existing neurological condition, prompt attention to other neurological signs that may accompany nystagmus, such as dizziness, may prevent or decrease the severity of nystagmus itself. Careful monitor of dosage of those drugs with nystagmus as a side effect may prevent the condition.
Parental concerns
Because nystagmus can be associated with many medical problems, the child with this condition must undergo a complete ocular and neurological evaluation.
Children with nystagmus are not aware that they may have a visual deficiency and as they get older must be helped with the restrictions that nystagmus places on them. For instance, driving may be restricted or not permitted. Certain occupations for which good visual correction is a requirement may be not feasible. Every effort must be made to integrate the child with nystagmus into a normal school setting in order to prepare the child for adult life, even if cosmetic concerns may instinctively lead the parent to want to protect the child.
Support for families of those with nystagmus can be found through the American Nystagmus Network.
KEY TERMS
Acupuncture —Based on the same traditional Chinese medical foundation as acupressure, acupuncture uses sterile needles inserted at specific points to treat certain conditions or relieve pain.
Albinism —An inherited condition that causes a lack of pigment. People with albinism typically have light skin, white or pale yellow hair, and light blue or gray eyes.
Autosomal —Relating to any chromosome besides the X and Y sex chromosomes. Human cells contain 22 pairs of autosomes and one pair of sex chromosomes.
Binocular —Affecting or having to do with both eyes.
Biofeedback —A training technique that enables an individual to gain some element of control over involuntary or automatic body functions.
Coloboma —A birth defect in which part of the eye does not form completely.
Lesion —A disruption of the normal structure and function of a tissue by an injury or disease process. Wounds, sores, rashes, and boils are all lesions.
Strabismus —A disorder in which the eyes do not point in the same direction. Also called squint.
X-linked —A gene carried on the X chromosome, one of the two sex chromosomes.
Resources
BOOKS
Halmagyi, G. Michael, and Phillip D. Cremer. "Central Eye Movements Disorders." Chapter 283 in Principles and Practice of Ophthalmology , 2nd ed. Philadelphia: Saunders, 2000.
Wheeler, David T. "Nystagmus." In Current Ocular Therapy 5. Philadelphia: Saunders, 2000, p. 407.
PERIODICALS
Hensil, Jennifer, and Andrew S. Gurwood. "Understanding Nystagmus." Optometry 71 (July 2000): 439–48.
Hertle, Richard W. "Examination of the Refractive Management of Patients with Nystagmus." Survey of Ophthalmology 45 (November-December 2000): 215–22.
Moster, Mark L. "Nystagmus." Ophthalmology Clinics of North America 14 (March 2001): 205–15.
WEB SITES
American Nystagmus Network. Available online at http://www.nystagmus.org/entry.html (accessed November 12, 2004).
Smith, Rodney J. "Solving the Diagnostic Puzzle of Congenital Nystagmus." Review of Optometry , June 1999 Case Report. Available online at http://www.revoptom.com/archive/issue/ro06f9.htm (accessed November 12, 2004).
Martha Reilly, OD