In the first video, the patient has both horizontal nystagmus and vertical “down-beat” nystagmus.
In the second video, the patient has a torsional nystagmus when looking to her right hand side.
Discussion of the sign
Nystagmus is defined as a rhythmic oscillation of the eyes. It usually consists of a slow drifting phase in one direction and a jerky corrective fast phase in the opposite direction. It is often classified into horizontal, vertical or torsional nystagmus. The direction of nystagmus is named according to the fast phase of eye movement by convention. In the first patient, the fast phase of the nystagmus is downward, and hence is termed vertical “down-beat nystagmus” (as opposed to “up-beat vertical nystagmus”). In the second patient, a rotatory component of the nystagmus is seen, and hence the nystagmus is termed “torsional nystagmus”. This is due to the influence of the three different semicircular canals, its pathology of which results in nystagmus in more than one direction, and thus the summation would cause a rotatory component to the nystagmus.
Nystagmus can be a physiological phenomenon. However, in the presence of other vestibular or central nervous system symptoms and signs, pathological causes should be considered. Often pathological causes of nystagmus can be classified into a central or peripheral cause. Central causes include cerebellar or brainstem lesions such as multiple sclerosis, stroke, tumour, spinocerebellar degeneration etc. Drug intoxication such as. due to anti-convulsants, alcohol and sedative hypnotics can also result in nystagmus. Peripheral causes of nystagmus include benign paroxysmal positional vertigo, labyrinthitis and Ménière’s disease.
Whilst the history and physical examination is important in differentiating the cause of nystagmus. Nystagmus which is vertical (e.g. in the first patient) is most likely due a central cause. Whilst nystagmus that is torsional, as in the second patient, is most likely due to a peripheral cause.