What is nystagmus?

Nystagmus (to nod) is the term applied to rapid involuntary oscillatory movement of the eyes independent of the normal eye movements. They are usually horizontal but vertical, rotatory or mixed movements may also be seen. The condition is almost always present in both eyes simultaneously.

What are the causes of this eye disorder?

The disorder may be present at birth or acquired later in life. The causative factors and associations are listed below.

Congenital nystagmus (present at birth)

Associated with albinism. 
Absence of Irises. 
Optic nerve malformations. 
Congenital cataract; if left unoperated within six months of birth, can lead to nystagmus. 
Acquired

Secondary to visual loss. 
Toxic ( alcohol intoxication , tranquilizers, sedatives, phencyclidine) 
Brain tumor. 
Head trauma. 
Stroke. 
Multiple sclerosis. 
Brain (thalamic) hemorrhage. 
Meniere's disease ( a disorder of the inner ear leading to episodes of impaired balance or vertigo). 
What are the signs and symptoms?

The symptoms depend on the age of onset. These are classified into three categories:

Congenital and early infantile nystagmus

The patient is totally unaware of the eye movements, since the objects being viewed do not appear to move. To and fro movements of the eyes are noticed by the parents or relatives. 
Vision is usually defective inspite of the correction, of the errors of refraction, which usually accompany the condition. 
Childhood nystagmus

If nystagmus is developed during childhood after the child has developed fixation, there are characteristic nodding movements of the head depending on the type and the direction of nystagmus. 
Acquired adult nystagmus

In cases of acquired adult nystagmus, the objects and surroundings often appear to move. Oscillopsia is the perception of the environment appearing to oscillate horizontally, vertically or torsionally. 
Patients frequently complain of blurred or unstable vision. 
Uncomfortable or abnormal head posturing may often be resorted to, in order to see clearly. 
Miner's nystagmus is a condition occurring chiefly in coal miners who work in dim lights for extended periods of time. They complain of 
Defective vision which worsens at night 
Headache 
Giddiness 
Intolerance on exposure to light (photophobia), 
Dancing of lights 
Movements of objects 
Note: Nystagmoid jerks must be differentiated from true nystagmus. These are larger rhythmic, jerky movements most pronounced at the extreme limits of normal movements. They are frequently encountered in unaffected people in conditions like fatigue.

How is it diagnosed?

Nystagmus is just a sign and not a disease per se. Hence it is important that the underlying condition be diagnosed at the earliest. Etiology of nystagmus may be arrived at by meticulous consideration of the following factors.

Age of onset 
Presence of oscillopsia 
History of squint 
Defective vision 
Functional blindness (amblyopia) 
Associated dizziness, giddiness and sense of losing balance 
Occupational history 
Drug or alcohol consumption 
Drug levels in urine and blood 
CT scan /MRI scan of the brain to evaluate intracranial pathology 
How is it treated?

Optical Aids (spectacles, prisms or contact lenses) - All refractive errors must be corrected before resorting to any further therapy. In case of manifest nystagmus; it is better to use contact lenses than spectacles. Amblyopia must be treated by occlusion, in which the good eye is covered and the patient is forced to use the defective eye. This is practised in children less than 10 years of age. 
Medications - In certain varieties of nystagmus, certain drugs may be of benefit like Baclofen, Gabapentin, Clonazepam. 
Biofeedback Training - Attempts have been made to convert the movements of nystagmus into audible stimuli, so that on hearing these sounds, the patient may voluntarily increase the tone of his eye muscles thereby eliminating the nystagmus. 
Surgery: It may be undertaken to correct the squint which may be associated with the nystagmus. Development of an abnormal head posture forms a definite indication for surgery.

Botox Injections: Severe disabling Nystagmus unresponsive to other therapies may require retrobulbar (behind the eyeball) injection of Botulinum Toxin (Botox), but this therapy is very expensive.