The eyes are the window to many aspects of our health. Involuntary eye movements may indicate neurological disorders, inner ear infection, or drug effects. The term nystagmus is defined in Reference 1 as “repetitive, to and fro, involuntary eye movements that are initiated by slow drifts”.
There are seven patterns of nystagmus:
1. Constant velocity drift of the eyes in the slow phase, followed by quick corrections.
2. When gazing away from center, drift back toward the center with a velocity the decreases exponentially with time, followed by quick corrections.
3. Drift away from the central position with an exponentially increasing velocity, followed by quick corrections.
4. Drift back and forth with a sinusoidal varying velocity.
5. Square wave jerks, with a period of about 20 milliseconds.
6. Macrosaccadic oscillations: quick jerks of the eyes around the position of what you're looking at.
7. Ocular flutter: a burst of saccades, typically at 10 to 15 cycles per seconds.
A neurologist will want to collect a history of nystagmus symptoms and perform an examination. The eye movements can be horizontal, vertical, rotational, or combination. It may be worse with the head in certain positions, or while the patient gazes in certain directions.
Nystagmus may or may not cause an illusion of motion of the outside world. Inner ear disorders cause eye symptoms primarily when the patient is in motion. Congenital nystagmus is present from birth and may not represent a serious condition.
Drug effects are a common cause of nystagmus. Alcohol, sedatives, and anticonvulsants such as gabapentin have been noted. Anticonvulsants are widely used for pain and psychiatric conditions, as well as their original use for epilepsy. Reference 2 reports that gabapentin (Neurontin) is a growing cause for impaired driving cases. Horizontal gaze nystagmus is one of the indicators of central nervous system depression.
If the cause is not drugs, inner ear disorder, or a congenital condition, then nystagmus may indicate a disorder of the brain and nerves.