Hippus

{{Short description|Pupillary response}}

Pupillary hippus, also known as pupillary athetosis, is spasmodic, rhythmic, but regular dilating and contracting pupillary movements between the sphincter and dilator muscles.{{cite journal |author1=McLaren J. W. |author2=Erie J. C. |author3=Brubaker R. F. | year = 1992 | title = Computerized analysis of pupillograms in studies of alertness | journal = Investigative Ophthalmology and Visual Science | volume = 33 | pages = 671–6 }}Cassin, B. and Solomon, S. Dictionary of Eye Terminology. Gainesville, Florida: Triad Publishing Company, 1990. Pupillary hippus comes from the Greek hippos meaning horse, perhaps due to the rhythm of the contractions representing a galloping horse.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. Notably, hippos in antiquity referred to involuntary eye movements which are nowadays called nystagmus.{{Cite journal |last=Gerb |first=Johannes |last2=Brandt |first2=Thomas |last3=Huppert |first3=Doreen |date=July 2023 |title=Historical descriptions of nystagmus and abnormal involuntary eye movements in various ancient cultures |url=http://journals.sagepub.com/doi/10.1177/00368504231191986 |journal=Science Progress |language=en |volume=106 |issue=3 |doi=10.1177/00368504231191986 |issn=0036-8504 |pmc=10469245 |pmid=37642983}}

It is particularly noticeable when pupil function is tested with a light, but is independent of eye movements or changes in illumination. It is usually normal, however pathological hippus can occur.

Pathologic hippus, the phenomenon of increased oscillation or their amplitude, is associated with aconite poisoning,Forensic and State Medicine: Reddy altered mental status, trauma, cirrhosis, and renal disease; suggesting a common pathway of frontal lobe dysfunction.{{cite journal |vauthors=Denny JC, Arndt FV, Dupont WD, Neilson EG | year = 2008 | title = Increased hospital mortality in patients with bedside hippus | journal = Am J Med | volume = 121 | issue = 3| pages = 239–45 | pmid = 18328309 | doi=10.1016/j.amjmed.2007.09.014}} A retrospective study of 117 hospitalized patients with hippus noted an increased 30-day mortality when compared to controls and adjusted for other factors.