Nystagmus

'Dancing eyes' or Nystagmus means uncontrolled movements of the eyes, from side to side, up and down or rotary. Thus Nystagmus could be horizontal, vertical or torsional. Sometimes, however the eyes can jerk sideways or up or down. These dance movements in the eyes could be in both or in just one eye. Interestingly, people with nystagmus are usually not aware of their eye movements.

Causes of Nystagmus

Abnormal function in the areas of the brain that control eye movements is usually the cause for the involuntary eye movements. It is that part of the inner ear that senses movement and position. Nystagmus syndrome can be present at birth or develop later in life because of a disease or injury. Nystagmus is usually infantile and is present from a very early age. Studies reveal that about one child out of every several thousand has nystagmus.

While the nystagmus that is present at birth is not severe, acquired nystagmus is caused by certain drugs or medicine. Such drugs include phenytoin or dilatin, an anti- seizure medicine, excessive alcohol or any other sedating medicine that can impair the labyrinth function. Acquired nystagmus may also be caused by any disease of the brain such as multiple sclerosis or brain tumor, when the areas controlling eye movements are damaged. Nystagmus may also be caused by congenital disease of the eye. This is rare and an ophthalmologist should evaluate a child with nystagmus to check any eye disease. Hyperventilation or flashing light in front of one eye, nicotine and vibrations are also known to cause nystagmus, but these are rare. Other causes of nystagmus include:

• Head injury from road accidents, mostly on motor bikes.
  
• Disorders of the inner ear such as labyrinthitis or Meniere's disease
  
• Stroke
  
• Thiamine or vitamin B12 deficiency.
  

Clinical manifestations

Nystagmus is a gradually developing condition leading to adverse effects. The severity of this condition is sometimes linked to congenital visual impairment. One of the important conditions associated with nystagmus is the lack of focus at a certain point. This happens because of the dispositional movement of the eye balls when the person turns the head from side to side. The classification of nystagmus gives a better understanding of the disease and its respective prophylaxis.

Different kinds of nystagmus

Manifest nystagmus which is present at all times, whereas latent nystagmus occurs only in one eye.

Manifest-latent nystagmus is continually present, but worsens when one eye is covered.

Congenital nystagmus is present at birth. The eyes swing like a pendulum in this condition. Strabismus is another term for this as the eyes do not necessarily work together all the time. It is associated with the oscillations that are horizontal in origin in the vestibular region. The occurrence of infantile nystagmus requires immediate attention as it may eventually lead to oculomotor disturbances causing permanent loss of vision.

Acquired nystagmus can be caused by diseases such as multiple sclerosis, brain tumor, diabetic neuropathy, accident and resulting head injury, neurological problem which could be side effect of a medication. This form of the disease is also referred as the see-saw nystagmus. It involves the impairment of the central or peripheral vestibular region. In this condition there a periodical oscillation of the eye which occurs in a rhythmic manner. There are many predisposing factors that contribute to the occurrence of this condition which include multiple sclerosis and any form of trauma affecting the head and neck.

There are two basic types of nystagmus. While the one is eye related 'optokinetic', the other is inner ear related 'vestibular'. Those with inner ear problems develop 'jerk nystagmus' where the eyes drift slowly in one direction and jerk back in the other direction. Chances are people with this condition can develop nausea and vertigo. However, this type of nystagmus is quite temporary. It can also occur in persons with Meniere's disease or when water settles into one ear. A decongestant can be taken to clear up nystagmus of this type.

Diagnosis of nystagmus

The following tests are done for diagnosis of nystagmus:

• CT scan of the head
  
• Electro oculography, which is an electrical method of measuring eye movements using tiny electrodes.
  
• MRI of the head
  
• Vestibular testing by recording the movements of the eyes.
  

History of the patient is taken and recorded, and a thorough physical examination is performed. The doctor would focus on the nervous system and inner ear. The doctor may ask the patient to wear a pair of goggles so that eyes could be magnified for the examination. Spin the patient for about 30 seconds, and stop and make her/him stare at an object. The patients' eye will first move slowly in one and then suddenly in the opposite direction. The eye movements of those suffering from nystagmus due to a medical condition will depend on the cause.

Treatment of nystagmus

The distressing fact is that there is no treatment for most cases of congenital nystagmus. Treatment for acquired nystagmus depends upon its cause. There are some instances when nystagmus. However, visual function of the patient with nystagmus can improve by some treatment. Prisms, surgeries such as tenotomy and drug therapies are used for infantile nystagmus. There are surgical treatments for people with nystagmus, and surgery usually reduces the null positions. Thus the head tilt is lessened and cosmetic appearance improves. Drug therapies include drugs such as botox or baclofen which reduce some nystagmic movements. But these results are usually temporary. Some with nystagmus benefit from biofeedback training. In some cases, wearing eyeglasses and contact lenses can help people with nystagmus see better. Contact lenses are a superior option to the glasses as the lens move with the eyes.

Some changes at home to help combat dizziness, visual problems or nervous system disorders can also be done to help the patients. And those children with nystagmus need special help in learning to adapt to school work and social conditions.

Electrooculography

Oculomotor is associated with the movements of the eye. These eye movements are both efferent and afferent in nature as they are regulated by one of the significant cranial nerves called the oculomotor nerve. These movements are recorded by using a technique called electrooculography. In most cases, this instrument is used to detect the blink amplitude and also drowsiness associated conditions. The relationship between the electrode potentials of the instrument and eye movements was first discovered and explained in 1849 by Du Bios Reymond. Significant research on this concept lead to the discovery of potential differences that exist between the cornea and retina of the eye.

The electro-oculography technique plays a significant role in the determination of resting potential of the eye. Over the years this technique has been extensively applied to identify the cause of drowsiness which is responsible for many accidents. The movements of the eye such as left, right, up and down are related to signal transmission mechanism which is powered by the brain through the oculomotor nerve. The electrooculography method detects the depolarization and repolarization differences caused both in the retina and cornea as a sequence which looking at an image and responding to it subsequently. These mechanisms are used to create a human computer interface system.

The tracking system was developed by administering the electrooculography technique. This system evaluates the distance of the person's gaze. The eye tracking and blink examinations performed using this method are essential in the determination of efferent and afferent activity of the nerves associated with the brain. The mechanism and categorization of the eye blink is also performed as it determines the neuromuscular activity of the respective system. An important observation in this evaluation is the measure of spontaneous blink time period. Under normal conditions spontaneous blinks are quick and are related to the reflex response. The duration of this blink is measured by using electrooculography to identify the presence of underlying Neuromuscular conditions. The electrooculogram values with respect to the movements of the eyes are linear in nature and hence the detection of wave form is significant.

In some cases, the electrooculography technique is used to determine the extent of alertness in person pertaining to eye movements and response to external stimuli. Electrodes are placed on the forehead and facial areas of the person to detect the activity of the oculomotor response. The activity of the eye in relation to the graph displayed on the monitor varies in different movements of the eye.