What causes downbeat nystagmus?
The most frequent causes were infarction, cerebellar and spinocerebellar degeneration syndromes, MS and developmental anomalies affecting the pons and cerebellum. Toxicity from anticonvulsant drugs probably caused nystagmus in a few patients.
What is the mechanism of nystagmus?
In health, there are three main control mechanisms for maintaining steady gaze—fixation; the vestibulo-ocular reflex; and a gaze-holding system (the neural integrator), which operates whenever the eyes are required to hold an eccentric gaze position1,2,3.
What does downbeat nystagmus mean?
Downbeat nystagmus (DBN) is characterized by a pathologic upward drift of gaze followed by a corrective downward saccade. DBN is most apparent when the patient is instructed to look down or to either side. It is typically accompanied by oscillopsia, which may be severe.
What is upbeat and downbeat nystagmus?
Downbeat and upbeat nystagmus are the directional counterparts of a vestibular tone imbalance in the pitch plane. The close proximity of the areas that cause either upbeat or downbeat nystagmus in the medulla is consistent with occasional transitions between the two conditions.
What is Oscillopsia?
Purpose of review: Oscillopsia is an illusion of an unstable visual world. It is associated with poor visual acuity and is a disabling and distressing condition reported by numerous patients with neurological disorders.
How do you describe nystagmus direction?
Nystagmus is a rhythmic regular oscillation of the eyes. It may consist of alternating phases of a slow drift in one direction with a corrective quick “jerk” in the opposite direction, or of slow, sinusoidal, “pendular” oscillations to and fro.
What causes vestibular nystagmus?
Vestibular nystagmus. Vestibular nystagmus, the most common type of nystagmus, is caused by dysfunction of the vestibular part of the inner ear, the nerve, the vestibular nucleus within the brainstem, or parts of the cerebellum that transmit signals to the vestibular nucleus.