Typical finding of left-sided benign paroxysmal positioning nystagmus caused by a canalolithiasis of the left posterior canal: the positioning maneuvers induced a vertical torsional nystagmus with the upper pole beating toward the left ear. This starts with a latency and has a crescendo-decrescendo time course. Thus the diagnosis of leftsided BPPV is proven.
When the patient turns his head to the right while lying on his back, there is a horizontal linear nystagmus beating towards the right, i.e. the right ear, with a crescendo-decrescendo time course. When the patient turns his head to the left while lying on his back (35 seconds), there is also a linear horizontal nystagmus with a crescendo-decrescendo time course, but a lower intensity. The affected side of a horizontal canal BPPB canalolithiasis is the side with the higher intensity of the nystagmus, i.e. in this case, the right horizontal canal. The nystagmus always beats geotropically.
Patient in the upright position: linear horizontal nystagmus beating to the right, which can last for hours, typical of cupulolithiasis of a horizontal canal. 5 seconds: Patient lies on his left ear: linear horizontal nystagmus beating toward the right ear, which can also last for hours. 45 seconds: Patient lies on his right ear, which induces linear horizontal nystagmus beating toward the left ear. In both cases, there is an ageotropically beating nystagmus. The affected ear is the ear with the lower intensity of nystagmus, i.e. in this patient, the left horizontal canal with a cupulolithiasis. Patient standing upright: head tilt to the right. Looking straight ahead (6 seconds) with the cover test reveals a skew deviation with the right eye below the left eye, the most sensitive test (20 seconds) is the alternating cover test which shows the maximum angle of deviation. So this patient has a latent skew deviation and the diagnosis can best be made using the alternating cover test. Examination of the patient in different eye positions (40 seconds) shows that the angle of deviation does not depend very much on the direction of gaze, which is typical for a skew deviation/vertical divergence. If the patient had, for instance, a trochlear palsy, the angle of deviation would depend very much on the direction of gaze. This is one of the criteria to differentiate between a skew deviation and a trochlear palsy or other eye-muscle or eyemuscle- nerve palsies.