What causes acquired nystagmus?

A few thoughts: Although any problem which can affect cerebellar/ brainstem connections could cause nystagmus, more often I see the problem secondary to medication reactions. Your listed meds do not seem to be the culprits. Problems within the inner ear will lead to abnormal eye movements, and not unique to see these with strokes, MS, and other disorders of brain. Most ophthalmologists can assist in diagnosis.

Drugs brain issues: Acquired nystagmus, a shaking of the eyes when this did not occur before, can be a side effect of certain drugs and also a sign related to central nervous system pathology. This should always be evaluated and the cause determined.