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.

Gaze Test

Gaze test or Horizontal Gaze Nystagmus Test - (HGN test) is one of the 3 Standardized Field Sobriety Tests (SFST) conducted by the police to check if the person is driving under the influence of alcohol. Nystagmus refers to involuntary rapid movements of the eyes that are caused by abnormal function in the areas of the brain that control eye movements. Nystagmus is caused by various conditions, one of which is alcohol consumption. Gaze test is a useful indicator of alcohol intoxication.

During the Gaze test, the police officer will hold a stimulus such as a flashlight or pen or even his finger in front of the driver's face and moves it sideways. The officer then observes the eyes of the driver as he follows the moving object horizontally with his eyes. The suspect's eyes may bounce or involuntarily jerk (nystagmus) if he is impaired due to alcohol consumption. The higher a person's blood alcohol content level, the more pronounced the nystagmus becomes.

As the subject's eyes follow the object, police will look for the following three indicators:

1. Whether the suspect was able to follow the object smoothly. Normal and sober person follows the stimulus whereas person under the influence of alcohol may have difficulty following the object.

2. The extent of stability of the eye at maximum deviation.

3. The angle at which the jerking begins. Jerking movements in the eye before the gaze reaches a 45-degree angle is indicative of a higher blood alcohol content level.

Gaze test is the most accurate test of all the sobriety tests and does not require any special equipment to conduct it. However gaze test requires a well trained police officer to read the eye movements.

Neuro Ophthalmologist

All vision problems need not necessarily stem from the eye. Some vision problems involve the brain. Neuro ophthalmology is the sub specialty of both neurology and ophthalmology. A neuro ophthalmologist is a Physician who specializes in the diseases affecting vision that originates from the nervous system. Conditions such as optic nerve disorders, loss of vision from central nervous system disease, double vision diplopia and involuntary movement of the eyes nystagmus are some of the disorders under the purview of a neuro ophthalmologist. An ophthalmologist attends to patients with disease or injury in the eye ball, cornea and the lens or into the eyeball at the retina inside the eye. If any problem occurs behind the eye in the optic nerve or in some distinct visual pathways connecting the brain, it requires the special skills of a neuro ophthalmologist.

A neuro ophthalmologist could be an ophthalmologist or a neurologist with additional special training. After completing a residency program in any one of the two specialty areas, they take a fellowship in neuro ophthalmology for a year or two before starting to practice as a neuro ophthalmologist. A neuro ophthalmologist attends to a full spectrum of neuro ophthalmic conditions including evaluation, diagnostic and referral services of rare and complex disorders. A neuro ophthalmologist caters to:

• Patients who suddenly lose part of their side vision.
  
• Patients suffering from double vision.
  
• Patients with unequal pupils.
  
• A patient suffering form a stroke.
  
• A patient with brain tumor
  
• Patients who suddenly have their vision out of focus
  
• Any and every patient with unusual vision problems.

In addition to the above, a neuro ophthalmologist provides emergency evaluation of a wide variety of disease that can cause visual loss. Unexplained visual loss can arise out of uncommon disease conditions like myasthenia gravis, multiple sclerosis, mitochondrial disease and other muscular diseases that affect the eye. The neuro ophthalmologist uses special testing techniques including visual fields, visual evoked response, imaging studies such as CT, MRI and Angiography and ultrasound to diagnose the disease patterns. It becomes necessary for the neuro ophthalmologist to work closely with other medical specialists to offer multidisciplinary care and solution for complex cases.