The pupils of a normal subject are generally described as equal, reacting by constriction or dilatation to various stimuli. Inequality of the pupils as an isolated finding is said to be relatively common, but impairment of the light reflex, especially in conjunction with pupillary inequality, is held to be strongly indicative, if not pathognomonic, of organic disease of the nervous system. An exception is the “tonic pupil,” for whose abnormally protracted reactions to light and accommodation an organic lesion has not yet been demonstrated. However, impairment of the light reflex is known to occur in subjects in whom there is no evidence of organic nervous disorder. These abnormalities of the light reflex have attracted little attention in this country, and are ignored almost entirely in text-books of neurology and psychiatry. Redlich (1908) made the important observation that muscular exertion might lead to dilatation of the pupil with impairment of the light reflex. Levine and Schilder (1942), in an extensive investigation of this phenomenon, concluded that muscular effort would produce dilatation and impairment of the light reflex in any pupil which initially retained its response to light, and would accentuate a pre-existing abnormality or bring out a latent tendency to impairment of the light reflex. Westphal (1907) first described the pupillary abnormality in catatonic schizophrenia to which the term “catatonic pupil” has been applied. This abnormality consists of pupillary dilatation with impairment of the light reflex, and is usually bilateral. The reactivity to light may vary from moment to moment, or from day to day; or pupillary rigidity may persist for a considerable time, with transient periods of brisk reactivity. Estimates of the frequency of the “catatonic pupil” vary remarkably—from 54 per cent. (Schilder and Parker, 1931) to 3.4 per cent. (Reichmann, 1913). Apparently a higher incidence has been found where repeated examinations have been carried out on the same subjects, but proper comparison is impossible, as the technique of examination has not been detailed by any of the authors.