it's pretty straight forward... once you've actually seen them. most nystag's are horizontal. when checking EOMs, be certain to keep the eyes deviated laterally for a few seconds (like 3-5.. yeah, that long). in normal people (w/o congenital nystag's), they'll remain stationary as you would expect. in folks with nystag's they'll actually "beat." most nystag beats that i've seen are no more than 2-3mm.
the same holds true for vertical nystags.
the real questions are (1) are the new, (2) why do they have them, and (3) to which side does the fast and slow beats go towards (helpful in ballance issues).
there a multitude of factors that can produce nystag's. my simple way of looking at them is FAR to simplistic to be of actual use, but will at least make you sound like you know _something_.
basically, nystag's are an OVER REACTION to a normal visual field presentation. we all have intrinsic nystags (mostly vertical ones) when we walk. that's how we can keep a fairly stationary perception of our surroundings when our eyes are moving up and down during ambulation. production of nystag's without a normal visual field input means, to me, that we're over correcting for something. the brain isn't interpreting things correcting. this can be either 1 of 3 places that deal without perception of the world during ambulation. (1) visual, (2) vestibular, or (3) somatosensory (though i would venture this is quite rare). if you jack up one of those systems to trick the brain into thinking you're moving, you'll produce nystag's. you DO trick the brain into this with the cold/hot caloric test for brain death.
new onset nystags are nearly ALWAYS pathologic of SOMETHING. i can't get you any further than that. sorry. i wouldn't feel great about sending a patient home with new onset nystags and no plan for w/u though.
take care,
davis
best of luck,
davis
