Nystagmus Descriptors
Type of nystagmus including both vertical and horizontal components
What is torsional nystagmus?
Delayed saccades and significantly reduced gain in smooth pursuit are interpreted this way.
Central involvement
OPK and this other oculomotor test share redundant pathways.
What is smooth pursuit testing.
These tests benefit from a fixation/no fixation comparison to help localize the impairment.
What are spontaneous gaze testing (with and without eccentric gaze) and static positional testing (e.g., head right, head left).
These are timing features that may be used to describe nystagmus
What are transient vs. persistent?
What is peripheral vestibular impairment (i.e., the patient could use fixation to reduce the nystagmus)
Saccades are generated when a command is sent from the frontal eye fields to this sensorimotor hub in the midbrain
What is the superior colliculus.
I can describe spontaneous nystagmus using these parameters:
What are direction, strength, duration (transient vs. persistent)
This nystagmus may or may not change with fixation in this phase
What is spontaneous nystagmus in the acute phase?
5 deg/s with and without fixation is suggestive of this type of disease state
What is acute; in the acute state the patient may struggle to use a fixation point to reduce nystagmus regardless of peripheral or central etiology.
This is the connection between the abducens nuclei on one side to the oculomotor nuclei on the opposite side.
What is the medial longitudinal fasiculus.
This is the difference between saccade latency and velocity.
What is initiation time (latency) vs. speed (velocity).
This type of nystagmus may be normal in gaze testing.
What is endpoint nystagmus?
5 deg/s right-beating nystagmus in gaze right; 7 deg/s left-beating nystagmus in gaze left is indicative of what type of pathology
What is central. This change in direction (from eccentric to primary) causing a change in nystagmus direction (left-beating to right-beating) is noted in rebound nystagmus (central characteristic).
Gaze evoked nystagmus could come from impairment in this structure.
What is the cerebellum (i.e., cerebellar lesions, structural changes like Chiari I, degenerative diseases)
Moving the head instead of the eyes during smooth pursuit testing will have this effect on gain.
What is decrease.
Left peripheral weakness may cause spontaneous nystagmus beating in this direction in the primary gaze position and change in this way in the gaze left position.
What is right beating nystagmus in the primary position and what is decrease in intensity in the gaze left position (according to Alexander's Law).
This central condition affects the medial longitudinal fasciculus so that adducting eye movements are slower than abducting eye movements
What is Internuclear ophthalmoplegia (INO)
This nystagmus pattern is suggest of this type of impairment:
Primary gaze: 5 deg/s right-beating
Gaze left: 2 deg/s right-beating
Gaze right: 8 deg/s right-beating
What is peripheral (b/c it follows Alexander's Law)
In this oculomotor test, symmetry is especially affected by spontaneous nystagmus.
What is optokinetic tracking.