Correct! This is downbeat nystagmus, an oscillation most commonly associated with disorders of the medulla or cerebellum. The offending disorder may be structural—Chiari malformation, tumor, stroke, inflammation—or caused by toxins, metabolic disorders, brain trauma, or neurodegenerative conditions. Many cases are idiopathic.

The nystagmus waveform is jerk, the fast component being mostly in the downward direction. It is best seen when the eyes are in eccentric gaze and looking downward. Because there is also a horizontal vector to the nystagmus trajectory, the eyes will be moving obliquely (“side pocket nystagmus”). If the nystagmus amplitude is great, patients will often report that viewed objects appear to be moving downward. Why downward? Because during saccades, vision is suppressed, so that the patient will see objects as moving only during the slow phase, in which the eyes are moving upward. As the eyes move upward, the retinas move in the opposite direction, so objects appear to move downward. This illusion is called “oscillopsia.” It occurs most prominently in forms of nystagmus that have wide-amplitude slow phases.

In relief of oscillopsia, several medications have been tried, none very successfully. Clonazepam and baclofen, often prescribed in the past, are not helpful; 4-aminopyridine (brand names Ampyra and Fampyra), which acts on cell membrane ion channels, may be more effective, but is expensive and not widely available.