DEFINITION
[Dancing eyes or jerking eyes]

Nystagmus is an involuntary, rhythmical, rapid movement or oscillations of the eyeball which may be horizontal, vertical, oblique, circular, rotatory, or mixed; in any or all fields of gaze; may be pendular (with undulating movements of equal speed, amplitude, and duration) or jerky (with slower movements in one direction, and faster in another to return to original position). The faster the rate, the smaller the amplitude (and vice versa). Vertical nystagmus is less frequent than horizontal nystagmus and is a sign of serious brain damage.

TYPES

• Nystagmus in Childhood
  This is basically a "Pendulum nystagmus" in which eye movements are pendular (with undulating movements of equal speed, amplitude, and duration, in each direction). The eyes rotate back and forth evenly. It leads to early vision loss; but may depend on the underlying condition. It worsens over time; from childhood to adulthood.
• Nystagmus Arising Later in Life
  Later in life, this occurs due to neurological dysfunction such as a head injury, multiple sclerosis or brain tumors. It leads to defects in movement of eyes called oscillopsia. It causes vertigo or dizziness.

The defect is classified according to the position of the eyes when it occurs:

• Grade I occurs only when the eyes are directed toward the fast component
• Grade II occurs when the eyes are in their primary position
• Grade III occurs even when the eyes are directed toward the slow component

CAUSE

• Defect in eye or visual pathway from the eye to the brain
• Other conditions like cataract, glaucoma, and albinism
• Acquired nystagmus leads to other conditions such as stroke, multiple sclerosis or even a blow to the head

SYMPTOMS

• Repetitive oscillations of the eye horizontally, vertically or rotary
• Head nodding and tilting
• Blurred or unstable vision
• Reduced acuity
• Dizziness or vertigo

DIAGNOSIS

• By irrigating an external auditory meatus with warm or cold water - The temperature gradient stimulates the vestibulocochlear nerve and the consequent nystagmus. 
• A special device called ElectroNystagmoGraph (ENG), a form of ElectroOculography (method of measuring eye movements using external electrodes) to quantify the recorded resulting eyes movement.

TREATMENT
There is no known treatment for Nystagmus.

• Use of  Prisms, Contact lenses, and Eyeglasses
• Strabismus Surgery
• Use of a Typoscope (card with a rectangular hole to view one word or line at a time)
• Use of an Underliner (card or strip of paper to "underline" the line being read)
• Muscle surgery (a repositioning of muscles to take advantage of the point of least nystagmus i.e. relative rest)