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Nystagmus


Nystagmus is characterized by an involuntary movement of the eyes, which may reduce vision or be associated with other, more serious, conditions that limit vision. Most frequently it is composed of a mixture of slow and fast movements of the eyes. Nystagmus can occur normally, such as when tracking a visual pattern. Nystagmus may also be abnormal, usually in situations where one would want the eyes to be still, but they are in motion.


The involuntary eye movements of nystagmus are caused by abnormal function in the areas of the brain that control eye movements. The exact nature of these disorders is poorly understood.

Muscles of the eye

There are six muscles that control the movement of each eye ball. The image shows the six muscles of the right eye.





TYPES

Nystagmus may be either congenital (present at birth) or may be acquired (caused by disease or injury later in life).


Congenital Nystagmus: It is the most common. It is usually mild, does not change in severity, and is not associated with any other disorder. Affected people are not aware of the eye movements, although they may be noticed by a careful observer. If the movements are of large amplitude, visual acuity (sharpness of vision) may be less than 20/20. Surgery may improve visual acuity.


Acquired Nystagmus: A less common cause of nystagmus is disease or injury of the central nervous system. The most common cause of acquired nystagmus is head injury from motor vehicle accidents in young people. In older people the most common cause is stroke (blood vessel blockage in the brain). Any disease of the brain (such as multiple sclerosis or brain tumors) can cause nystagmus if the areas controlling eye movements are damaged. Because control of eye movements is affected by input from the labyrinth (the part of the inner ear that senses movement and position), inner ear disorders (such as Meniere's disease) can also lead to acquired nystagmus. Other causes include Dilantin (an antiseizure medication), toxicity, and alcohol intoxication.



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.

"Rule" for Sensory (Pendular) Nystagmus

Vision loss

Nystagmus

Before 2 years*

Always

Before 4 years

Often

After 6 years

Never

* This nystagmus is not present at birth but develops by approximately 6 months.





CAUSES

Nystagmus may be inherited, be idiopathic (no known cause), or be associated with a sensory problem; its direct cause is an instability in the motor system controlling the eyes.


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:

  • Albinism. This condition is caused by a decrease in pigmentation and may affect the eyes.

  • Disorders of the eyes. This may include optic atrophy, color blindness, very high nearsightedness (myopia) or severe astigmatism, or opacities in the structures of the eyes.

  • Acute labyrinthitis. This is an inflammation in the inner ear. The patient may have dizziness (vertigo), nausea and vomiting, and nystagmus.

  • Brain lesions. Disease in many parts of the brain can result in nystagmus.

  • Alcohol and drugs. Alcohol and some medications (e.g., anti-epilepsy medications) can induce or exaggerate nystagmus.

  • Multiple sclerosis. A disease of the central nervous system.

Nystagmus can run in families, and it has been known to be passed down to the next generation, but can also skip generations.




DIAGNOSIS



Diagnosis is made clinically based on the medical history and physical examination.


Diagnostic tests that may be performed include:

  • CT scan of the head or MRI of the head

  • Electro-oculography: An electrical method of measuring eye movements using tiny electrodes.

TREATMENT

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.




Adjunctive therapeutic modes (e.g., Fresnel prisms (Prisms that make up a Fresnel lens bend and magnify light rays, creating a single, concentrated beam of light) and orthoptic (Orthoptics refers to how well the two eyes work together as a team) exercises) can also be beneficial. PAN and see-saw nystagmus can be treated with baclofen. Downbeat nystagmus may respond to clonazepam therapy, and prisms may help if the nystagmus can be modified with convergence. Congenital nystagmus may respond minimally to drugs (e.g., baclofen), but prisms or surgical procedures, or both, are still the primary treatment modalities.







Near Point of Convergence Exercises:

“An accommodative target, such as the point of a pencil (i.e., pencil push-ups), is placed remote to the patient’s near point of convergence and gradually brought toward the tip of the nose with the patient converging to avoid diplopia. Just before there is a break in fusion, the patient holds fixation the target for 10 seconds. This so-called push-up is repeated 10 times, 2-4 times a day, until the patient is able to hold fixation to the tip of the nose. The exercises can be tapered and then used on an as-needed basis when the patient notices a recurrence of symptoms.”





Diet and Nystagmus

Two case reports illustrate the therapeutic response of congenital nystagmus to a diet eliminating synthetic food colors, synthetic food flavors, the antioxidant preservatives butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), and a small group of foods thought to contain a natural salicylate radical. For more. click here


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