Nystagmus (click title for video)
DEFINITION: rhythmical oscillation of the eyeballs (click here for video)
at least 37 different kinds are recognized
- commonly used to refer to JERKY NYSTAGMUS:
- slow drift of the eyes in one direction (PURSUIT) followed by a rapid recovery movement in the opposite direction (SACCADE)
direction is named for the fast component:
i.e, a rightward nystagmus consists of slow movement of eyes to the left, followed by fast recovery to the right
can be induced in normal individuals by vestibular stimulation (see experiments listed below) - nystagmus in the absence of vestibular stimulation indicates some kind of pathology
PURSUIT is controlled by vestibulo-ocular reflex
SACCADE is controlled by higher centers (e.g., cortex)
induction of nystagmus is a clinically useful mechanism for assessing brain function (caloric test)
- normal patient: NYSTAGMUS (PURSUIT + SACCADE)
- loss of cortical function: PURSUIT ONLY
- brainstem death: neither pursuit nor saccade
EXPERIMENTS TO TRY (IF YOU DARE):
- In a large open space, on a soft surface (such as snow or grass), take hold of a heavy object at arms length (maybe a backpack full of all your Neuro notes) and spin around, leaning slightly backwards to balance the bag. Spin around 10-20 times at a rate of about 2 revolutions /second.
- Alternatively, if you don't want to injure yourself by falling over, sit in an "executive" swivel chair and have someone spin you around as fast as they can for 20-30 seconds.
- In both cases, you will experience rotatory vertigo for a few seconds when you stop rotating. You will have the sensation you are still spinning, your eyes will exhibit nystagmus (a beating from side to side) and if you continue, you may experience nausea. Based on this experience, you now partially understand the problem of vertigo.