Hippus is an abnormal 'flickering' of the pupil of the eye. We all have rhythmic contraction and dilation of the pupil, which normally occurs at about 1.4 Hz. In hippus, this is abnormally exaggerated and speeded up, giving a bizarre quivering appearance to the pupil. I've only ever seen this in one patient in the ICU with a severe stroke (severe as in on the vent for 3 months, on a cooling blanket to try to keep his temperature under 107 degrees, on every medication known to man etc. etc.). Generally hippus is associated with neurosyphilis, multiple sclerosis and myasthenia gravis. Very unusual and rare finding. Also extremely freaky when you're the one who discovers it...