Hippus
Pupillary hippus, also known as pupillary athetosis, is spasmodic, rhythmic, but regular dilating and contracting pupillary movements between the sphincter and dilator muscles.[1][2] Pupillary hippus comes from the Greek hippos meaning horse, perhaps due to the rhythm of the contractions representing a galloping horse.[3] Notably, hippos in antiquity referred to involuntary eye movements which are nowadays called nystagmus.[4]
It is particularly noticeable when pupil function is tested with a light,[2] but is independent of eye movements or changes in illumination.[1] It is usually normal, however pathological hippus can occur.[2][3]
Pathologic hippus, the phenomenon of increased oscillation or their amplitude, is associated with aconite poisoning,[5] altered mental status, trauma, cirrhosis, and renal disease; suggesting a common pathway of frontal lobe dysfunction.[6] A retrospective study of 117 hospitalized patients with hippus noted an increased 30-day mortality when compared to controls and adjusted for other factors.[6]
