Definition
- A common definition of nystagmus is an involuntary, rhythmic, ocular oscillation. Numerous forms of nystagmus exist, so a practical approach to analyzing nystagmus is essential to determine its underlying cause.
Evaluation of Nystagmus
- The following steps provide a clinical approach to the evaluation of nystagmus.
A. Assess its PLANE: whether the nystagmus is horizontal, vertical, torsional, or some combination of these.
B. Assess its TYPE: pendular nystagmus denotes nystagmus in which both phases of eye movement are of equal amplitude whereas jerk nystagmus denotes nystagmus that involves a slow drift and quick correction.
C. If JERK NYSTAGMUS is present, assess its direction: unidirectional nystagmus denotes nystagmus that maintains a consistent direction whereas bidirectional nystagmus changes depending on the direction of gaze. For instance, spontaneous, vestibular nystagmus is unidirectional: it never changes direction but it increases as the patient looks in the direction of the fast component of the jerk nystagmus. On the contrary, gaze-evoked nystagmus is bidirectional: for instance, on right gaze, it is right beating and on left gaze, it is left beating. Note that the jerk nystagmus is named for direction of the fast component.
D. Assess the amplitude and rate: commonly, the smaller the amplitude, the faster the rate. See:
descriptive terminology for rate and amplitude.
E. Assess for the NULL POINT where the nystagmus is minimal or absent: the patient may adapt a head turn or tilt to consistently place the eyes at the null point.
F. Assess whether the nystagmus is binocular or monocular and if it is binocular whether it is conjugate (both eyes move in the same direction) or disconjugate (the eyes move in different directions).
G. Assess whether changes in head position modulate the nystagmus. Spontaneous nystagmus denotes nystagmus that is unmodulated by changes in head position whereas positional nystagmus denotes nystagmus that is modulated by changes in head position (see The Dix-Hallpike Maneuver).
H. Assess for latent nystagmus: manifest nystagmus denotes nystagmus that is present when both eyes are viewing a target whereas latent nystagmus is nystagmus that occurs when one eye is covered. Latent nystagmus is a binocular, conjugate nystagmus — the quick phases of both eyes beat toward the uncovered (fixating) eye.
I. Assess for associated rhythmic movements of non-ocular structures, such as the face, palate, neck, or limbs, such as oculopalatal myoclonus.
