This article reviews the pupil light reflex and its reaction pathway. The pupil light reflex is considered to be a simple subcortical reflex. However, many studies have proven that patients suffering from isolated occipital lobe lesions with homonymous visual field defects showed pupillary hemihypokinesia, i.e., reduced or absent pupil light responses to perimetric stimuli in the blind part of the visual field. In this article, the old hypotheses of pupillary hemihypokinesia are verified based on new findings.

Since the discovery of melanopsin-containing retinal ganglion cells, the common knowledge about the pupil has been changing. It is possible that the descriptions for the basic pathway of the pupil light reflex in textbooks will be changed in the future.