Nystagmus is a vision condition in which the eyes make repetitive, uncontrolled movements, often resulting in reduced vision. These involuntary eye movements can occur from side to side, up and down, or in a circular pattern. As a result, both eyes are unable to hold steady on objects being viewed. Nystagmus may be accompanied by unusual head positions and head nodding in an attempt to compensate for the condition.
Nystagmus can be inherited and appear in early childhood or develop later in life due to an accident or illness. Generally, nystagmus is a symptom of some other underlying eye or medical problem. However, the exact cause is often unknown.
Persons with nystagmus may experience reduced visual acuity. They may also have problems with depth perception that can affect their balance and coordination. Nystagmus can be aggravated by fatigue and stress.
Most individuals with nystagmus can reduce the severity of their uncontrolled eye movements and improve vision by positioning their eyes to look to one side. This is called the "null point" where the least amount of nystagmus is evident. To accomplish this they may need to adopt a specific head posture to make the best use of their vision.
The forms of nystagmus include:
- Congenital - most often develops by 2 to 3 months of age. The eyes tend to move in a horizontal swinging fashion. It is often associated with other conditions such as albinism, congenital absence of the iris (the colored part of the eye), underdeveloped optic nerves, and congenital cataract.
- Spasmus nutans - usually occurs between 6 months and 3 years of age and resolves spontaneously between 2 and 8 years of age. Children with this form of nystagmus often display head nodding and a head tilt. Their eyes may move in any direction. This type of nystagmus usually does not require treatment.
- Acquired - develops later in childhood or adulthood. The cause is often unknown, but it may be due to central nervous system and metabolic disorders or alcohol and drug toxicity.
Nystagmus can be further classified by the type of motion the eyes make:
- Pendular nystagmus - the speed of movement of the eyes is in same in both directions.
- Jerk nystagmus - the eyes move slowly in one direction and then quickly "jerk" back in the other direction.
What causes nystagmus?
Nystagmus results from the instability or impairment of the system responsible for controlling eye movements. When nystagmus develops in early childhood, it can be caused by a problem with the visual pathway from the eye to the brain. Often the child has no other eye or medical problem. Acquired nystagmus, which occurs later in life, can be the symptom of another condition such as stroke, multiple sclerosis or a blow to the head.
Other causes of nystagmus include:
- Lack of development of normal eye movement control early in life
- Very high refractive error, e.g. nearsightedness (myopia) or astigmatism
- Congenital cataracts
- Inflammation of the inner ear
- Medications such as anti-epilepsy drugs
- Central nervous system diseases
How is nystagmus diagnosed?
Nystagmus can be diagnosed through a comprehensive eye exam. Testing for nystagmus, with special emphasis on how the eyes move, may include:
- Patient history to determine any symptoms the patient is experiencing and the presence of any general health problems, medications taken, or environmental factors that may be contributing to the symptoms.
- Visual acuity measurements to assess the extent to which vision may be affected.
- A refraction to determine the appropriate lens power needed to compensate for any refractive error (nearsightedness, farsightedness, or astigmatism).
- Testing how the eyes focus, move and work together. In order to obtain a clear, single image of what is being viewed, the eyes must effectively change focus, move and work in unison. This testing will look for problems that affect the control of eye movements or make it difficult to use both eyes together.
Since nystagmus is often the result of other underlying health problems, your optometrist may refer you to your primary care physician or other medical specialist for further testing.
Using the information obtained from testing, your optometrist can determine if you have nystagmus and advise you on treatment options.
How is nystagmus treated?
Nystagmus can not be cured. While eyeglasses and contact lenses do not correct nystagmus, they can help to correct other vision problems such as nearsightedness, farsightedness or astigmatism.
Some types of nystagmus improve throughout childhood. In addition, vision may be enhanced with prisms and special glasses. The use of large-print books, magnifying devices and increased lighting can also be helpful.
Rarely, surgery is performed to alter the position of the muscles, which move the eyes. While it does not cure nystagmus, it may reduce the amount of head turn needed for best vision.
Treatment for other underlying eye or medical problems may help to improve or reduce nystagmus.