Abstract
Nystagmus is defined as rhythmic, most often involuntary eye movements. It normally
consists of a slow (pathological) drift of the eyes, followed by a fast central compensatory
movement back to the primary position (refixation saccade). The direction, however,
is reported according to the fast phase. The cardinal symptoms are, on the one hand,
blurred vision, jumping images (oscillopsia), reduced visual acuity and, sometimes,
double vision; many of these symptoms depend on the eye position. On the other hand,
depending on the etiology, patients may suffer from the following symptoms: 1. permanent
dizziness, postural imbalance, and gait disorder (typical of downbeat and upbeat nystagmus);
2. if the onset of symptoms is acute, the patient may experience spinning vertigo
with a tendency to fall to one side (due to ischemia in the area of the brainstem
or cerebellum with central fixation nystagmus or as acute unilateral vestibulopathy
with spontaneous peripheral vestibular
nystagmus); or 3. positional vertigo. There are two major categories: the first
is spontaneous nystagmus, i.e., nystagmus which occurs in the primary position as
upbeat or downbeat nystagmus; and the second includes various types of nystagmus which
are induced or modified by certain factors. Examples are gaze-evoked nystagmus, head-shaking
nystagmus, positional nystagmus, and hyperventilation-induced nystagmus. In addition,
there are disorders similar to nystagmus, such as ocular flutter or opsoclonus. The
most common central types of spontaneous nystagmus are downbeat and upbeat, infantile,
pure torsional, pendular fixation, periodic alternating, and seesaw nystagmus. Many
types of nystagmus allow a precise neuroanatomical localization: for instance, downbeat
nystagmus, which is most often caused by a bilateral floccular lesion or dysfunction,
or upbeat nystagmus, which is caused by a lesion in the midbrain or medulla. Examples
of drug treatment are the use of
4-aminopyridine for downbeat and upbeat nystagmus, memantine or gabapentin for
pendular fixation nystagmus, or baclofen for periodic alternating nystagmus. In this
article we are focusing on nystagmus. In a second article we will focus on central
ocular motor disorders, such as saccade or gaze palsy, internuclear ophthalmoplegia,
and gaze-holding deficits. Therefore, these types of eye movements will not be described
here in detail.
Key words
neuro-ophthalmology - nystagmus - pharmacology
