Nystagmus series – Part III
(downbeat nystagmus)
"definers of modern neuro-ophthalmology"
2) Pathophysiology
3) Associated symptoms
4) Fixation in central vestibular nystagmus
“poorly suppressed by fixation of a visual target”
- abnormal smooth-pursuit system
5) Making downbeat nystagmus more noticeable
Alexander’s law
- looking down and laterally
Bedside maneuvers
- change head position
- vigorous head-shaking
- hyperventilation
- mastoid vibration
6) Obs
a) often, downbeat nystagmus is associated w/ horizontal gaze-evoked nystagmus
b) slow-phase without specific waveform
c) convergence does not specific change nystagmus features
d) downbeat nystagmus greatest on up gaze; vertical gaze-holding impair
e) rarely disjunctive
7) Downbeat nystagmus - features
i) evoked by looking down and laterally
ii) no suppress by visual fixation
iii) vestibulocerebellar involvement
8) Downbeat nystagmus
9) Downbeat nystagmus
10) Downbeat nystagmus
11) Downbeat nystagmus
12) Downbeat nystagmus
13) Downbeat nystagmus
14) Downbeat nystagmus
15) Downbeat nystagmus
16) Downbeat nystagmus
17) Downbeat nystagmus
18) Differ
downbeat nystagmus vs ocular bobbing
ocular bobbing
"spontaneous downward jerks of eyes with slow return to midposition in association with paralysis of spontaneous and reflex horizontal eye movements"
- pontine lesion