To the Editor. —Hippus is a queer old word and a catchy one. It has been around a long time and refers to a restless mobility of the pupil, a tendency for the pupil size to fluctuate and to bounce up and down when you expect it to be stable. The word is related to the Greek hippos, a horse, and one is tempted to assume that it is an allusion to some jogging equestrian motion. It is said that hippus once meant a twitching of the eyelids, and that at one time it was synonymous with nystagmus, but for at least 150 years it has referred only to the pupil and has not been used to describe other occular movements. During the 19th century many clinical correlations of dubious value were made between hippus and various dire afflictions, including especially migraine, epilepsy, neurasthenia, brain tumor, hysteria, syphilis, myasthenia and