3. When the nystagmus is unidirectional (ie, nystagmus beating on the same side independent of the gaze direction) we will performed the Head Impulse Test (HIT)(13). When an acute lesion occurs on one labyrinth, the input from the opposite side is unopposed and as a result, when the head is rapidly moved toward the affected side, the eyes will be initially pushed toward that side and, immediately after, a corrective eye movement (corrective "saccade") back to the point of reference is seen. When the corrective "saccade" is present the HIT is considered positive and it indicates non-central AV, whereas a negative HIT indicates central vertigo(14).