Hippus

Template:Short description Pupillary hippus, also known as pupillary athetosis, is spasmodic, rhythmic, but regular dilating and contracting pupillary movements between the sphincter and dilator muscles.<ref name="McLaren">Template:Cite journal</ref><ref name="Cassin">Cassin, B. and Solomon, S. Dictionary of Eye Terminology. Gainesville, Florida: Triad Publishing Company, 1990.</ref> Pupillary hippus comes from the Greek hippos meaning horse, perhaps due to the rhythm of the contractions representing a galloping horse.<ref name="Beatty">Beatty, J., & Lucero-Wagoner, B. (2000). The pupillary system. In J. T. Cacioppo, L. G. Tassinary & G. G. Bernston (Eds.), The handbook of psychophysiology (2nd ed.) (pp. 142-162). USA: Cambridge University Press.</ref> Notably, hippos in antiquity referred to involuntary eye movements which are nowadays called nystagmus.<ref>Template:Cite journal</ref>

It is particularly noticeable when pupil function is tested with a light,<ref name="Cassin"/> but is independent of eye movements or changes in illumination.<ref name="McLaren"/> It is usually normal, however pathological hippus can occur.<ref name="Cassin"/><ref name="Beatty"/>

Pathologic hippus, the phenomenon of increased oscillation or their amplitude, is associated with aconite poisoning,<ref name="Reddy">Forensic and State Medicine: Reddy</ref> altered mental status, trauma, cirrhosis, and renal disease; suggesting a common pathway of frontal lobe dysfunction.<ref name="Denny">Template:Cite journal</ref> A retrospective study of 117 hospitalized patients with hippus noted an increased 30-day mortality when compared to controls and adjusted for other factors.<ref name="Denny" />

See also

• Athetosis
• Anisocoria - condition characterized by an unequal size of the eyes' pupils.