Hippus

Hippus, also known as pupillary athetosis, is spasmodic, rhythmic (< 0.04 Hz), but irregular dilating and contracting pupillary movements between the sphincter and dilator musclesMcLaren, J. W., Erie, J. C. and Brubaker, R. F. (1992). Computerized analysis of pupillograms in studies of alertness. "Investigative Ophthalmology and Visual Science, 33", 671-6.] Cassin, B. and Solomon, S. "Dictionary of Eye Terminology". Gainsville, 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 horseBeatty, 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.] .

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.

Hippus has been classically been noted as sign of Aconite poisoning. [4]

References

4. Forensic and State Medicine: Reddy