Pendular nystagmus consists of a slow phase that is a sinusoidal oscillation rather than a unidirectional drift.  Quick phases may be superimposed. 
The nystagmus may result in oscillopsia, nausea, disorientation and instability when acquired, and is often associated with tremor of the head and limbs as well as truncal titubation and ataxia.

Acquired pendular nystagmus is characterised by:

• Sinusoidal oscillations, in the range of 2-6 Hz  (rather than unidirectional drift and quick phase).  Pendular nystagmus can become more jerky on eccentric gaze. 
• Elliptical appearance, depending upon the presence and relative phase of a sinusoidal vertical and horizontal component; oblique trajectories are rare, however torsional components are not uncommon. 
• Acquired pendular nystagmus in oculopalatal myoclonus has a slower frequency of 1- 3 Hz, is irregular, and is of larger amplitude and faster velocity than the acquired pendular nystagmus in demyelinating diseases.

The nystagmus is frequently dysconjugate and may even be horizontal in one eye and vertical in the other. 

Causes

1. Lesions of the Guillain-Mollaret triangle, classically demyelinating diseases, or stroke.
2. Toluene toxicity from glue sniffing¹.
3. Disorders of myelination (Pelizaeus-Merzbacher disease)
4. Pendular nystagmus in a seesaw pattern (with elevation and intorsion of one eye and depression and extorsion of the other eye in one half cycle and the reverse pattern in the other half cycle) has been reported with chiasmal pathology with an accompanying bitemporal hemianopia or with cerebellar lesions¹.
5. Pendular oscillations that are about 180° out of phase in the horizontal plane causes a type of convergent-divergent nystagmus, sometimes with associated oscillatory movements of the jaw, face, or limbs (oculomasticatory myorhythmia) and vertical gaze palsy. This is classically seen in Whipple's Disease.

Treatment

1. Acquired pendular nystagmus in demyelinating disease often responds to moderately high medication doses, but in oculopalatal tremor, it tends to be treatment resistant.
2. Memantine. 5 mg/d orally ; increase by 5 mg/wk to maximum daily dose of 20 mg (10 mg 2 times a day)
3. Gabapentin
4. Clonazepam, valproate, and scopolamine may be effective in some patients. Beneficial outcomes have been reported in some cases with combined medical and surgical intervention, with surgical procedures more classically used in congenital nystagmus¹.

In the upper black-and-white eye movement videos, note the predominantly horizontal sinusoidal back-to-back slow oscillations without any fast phases.
The bottom portions of the video show the eye position (red line is horizontal eye position, blue line is vertical eye position) and velocity (purple and green lines) traces of the nystagmus. The sinusoidal oscillation in the red line corresponds to the horizontal oscillations of the eyes. A slight vertical oscillation is also seen. Note the similarity of the red line to the graphic representation of pendular nystagmus in Figure 1D of the section: Nystagmus.

(vv)Pendnys1.mp4(tt)

1. The first video segment shows minimal to no movement in the right eye and small horizontal pendular oscillations in the left eye.
2. The second segment shows a magnified view of the right eye, with minimal to no visible movement in the right eye.
3. The third segment shows a magnified view of the left eye, with small horizontal pendular oscillations.
4. The fourth video segment shows marked saccadic hypermetria (overshooting of the target with saccades), evidence that this patient also had cerebellar dysfunction, as is typical of most patients with acquired pendular nystagmus from multiple sclerosis.

(vv)2Nd Pend Nys.mp4(tt)

Video shows a patient with oculopalatal tremor with asymmetric pendular nystagmus. The movement is vertical-torsional in the right eye and predominantly torsional in the left eye with smaller-amplitude movement

(vv)Acqpendfirstnys.mp4(tt)