Figure 2.

Mechanism of canalolithiasis of BPPV of the horizontal semicircular canal, when the left ear is affected (the involved left horizontal canal is colored black). (a) Patient in supine position with debris in the posterior part of the left horizontal canal. (b) When rotating the head towards the affected side, particles move towards the ampulla, producing an ampullopetal flow and triggering intense geotropic horizontal nystagmus. (c) When rotating the head towards the healthy side, particles fall in the opposite direction, causing an ampullofugal flow and triggering nystagmus beating again towards the ground, but less intense.