Nystagmus is a term to describe fast, uncontrollable movements of the eyes that may be:
- Side to side (horizontal nystagmus)
- Up and down (vertical nystagmus)
- Rotary (rotary or torsional nystagmus)
The term “dancing eyes” has been used to describe Nystagmus. Perhaps the most famous individual with Nystagmus is flutist James Galway. It hasn’t seemed to hamper him!
The involuntary eye movements of Nystagmus are caused by abnormal function in the areas of the brain that control eye movements. The part of the inner ear that senses movement and position (the labyrinth) helps control eye movements.
There are two forms of Nystagmus:
- Congenital Nystagmus
- Acquired Nystagmus: Develops later in life because of a disease or injury.
Nystagmus eye movements can either be pendular (roughly equivalent speed in each direction) or jerk (where there is a fast movement in one direction and a slower recovery movement in the opposite direction). Pendular Nystagmus is usually found in Congenital Nystagmus, while jerk Nystagmus is present in Acquired Nystagmus.
Congenital nystagmus is usually mild and does not worsen over time. People with this condition do not see the world moving, nor can they see their eyes moving in a mirror. However, they can see their eye movements if they see themselves on TV, in a film or video. The eye movements are characterized by the range of the movement (small, medium or large angle) and frequency (slow, medium or fast oscillations). In almost all cases visual acuity is reduced. Astigmatism and eye-turns (strabismus) are also frequently present with individuals with congenital nystagmus.
Nystagmus may be caused by a number of genetic visual disorders including:
- Optic Nerve Hypoplasia
- Congenital Cataracts
- Retinopathy of Prematurity
The most common cause of acquired nystagmus is certain drugs or medication. Phenytoin (Dilantin) – an antiseizure medication, excessive alcohol, or any sedating medicine can impair the labyrinth’s function.
Other causes include:
- Head injury from motor vehicle accidents
- Inner ear disorders such as labyrinthitis or Meniere’s disease
- Thiamine or vitamin B12 deficiency
- Multiple Sclerosis (MS)
Most individuals with nystagmus have some degree of reduced visual acuity; making reading print, seeing signs, TV, recognizing faces and driving difficult if not impossible.
Despite this issue many people with these disorders can attend school, learn normally and lead full and active lives.
There is no medicine, surgery, eyeglasses or contact lenses available to correct nystagmus. Eyeglasses or contact lenses may be prescribed to sharpen vision when there are refractive errors present such as farsightedness (hyperopia), nearsightedness (myopia) and astigmatism, but these glasses will not return the vision to normal. Occasionally the best eyeglass prescription can lessen the degree of the nystagmus which may also modestly improve visual acuity.
Magnification can be very helpful to improve the vision of individuals with nystagmus. Using larger print, or holding reading material close to the eyes (which in effect enlarges the print), strong reading glasses and optical and electronic magnifiers can also be helpful. Software to enlarge the print on computer screens, and even read the text, can make computer use much more efficient.
Proper lighting can be very helpful to maximize visibility and eye comfort. Stand lamps with special bulbs some with goosenecks make optimizing illumination quick and easy.
Handheld telescopes (monoculars) and telescopes mounted into eyeglasses (bioptic telescopes) can make distance vision almost as good as normal, allowing individuals to see the teacher, classmates and blackboard in class, read signs while shopping and traveling, read the computer and play music, cards and board games at normal distances.
Nystagmus does not usually interfere with the effective use of telescopic devices. If the angle of movement is quite large, often Galilean telescopes with large eye lenses are most effective. If the angle of movement is less dramatic, Keplerian telescopes that offer wider fields of view, especially at higher powers, can be very useful.
As discussed above, eye movements in nystagmus are characterized by the angular degree of the movement (small, medium or large angle) and frequency of movement (slow, medium or fast oscillations).
Most individuals with nystagmus have a null point (an eye position where the eyes move the least) where vision is usually the most clear. This position may be staright ahead (primary gaze), or may be located to one side or the other, or even up or down. In these cases the individual may adopt an unusual head posture which allows them to minimize their eye movements. Sometimes surgery or eyeglasses with prism ican be prescribed that can provide the preferred eye position while allowing the individual to have more normal posture. In either event, the individual should be encouraged to assume what ever posture they find most comfortable.
The ability to judge depth is derived from the two eyes working together called binocular vision. Since a misalignment of the eyes (strabismus) can be present in individuals with nystagmus, the ability to judge distances based upon binocular vision (stereopsis) will be reduced or absent. Individuals without binocular vision can learn to make depth judgments using other visual cues. A very helpful book to learn to make depth judgments without binocular vision is the “Singular View” by Frank Brady.
Nystagmus Arising Later in Life
Nystagmus that develops later in life usually is a result of neurological disorders such as a head injury, multiple sclerosis, drug reactions or brain tumors. Unlike childhood nystagmus, individuals with late onset nystagmus will notice that objects seem to move. This is called oscillopsia. Oscillopsia can cause vertigo or dizziness undermining balance making walking and many other activities difficult.
Late onset nystagmus usually shows a jerk eye movement—fast in one direction, and slow in the opposite direction. The degree of nystagmus may change as the individual looks in different directions.