Effect of 3,4-Diaminopyridine on the Gravity Dependence of Ocular Drift in Downbeat Nystagmus

Background: The pathomechanism of downbeat nystagmus (DBN) remains controversial but each mechanism has to account for (i) its gaze evoked vertical centripetal drift which increases with vertical gaze eccentricity, and (ii) the vertical bias component of the upward slow phase velocity on gaze straight ahead. The vertical velocity bias has a gravity-dependent component which leads to maximal drift velocity when patients lie in a prone position and minimal in a supine position. Recently, the potassium channel blocker 3,4-diaminopyridine (3,4-DAP) has been shown to be effective in DBN of patients with the head upri…