This condition of the pupil is produced artificially by poisoning with opium or with calabar bean. The pupil is sometimes contracted to the size of a pin-head, or even less. This condition may also arise from paralysis of one of the nerves of the eye, or from irritation of the third nerve, which supplies the eye. It sometimes results from long use of the eyes in viewing minute objects, as in the study of microscopy, watch-making, reading, etc. It is also a symptom in some affections of the spine, and in inflammation of the brain.

Irregular contraction of the pupils, one being large and the other small, is also observed in some cases of cerebral disease. Nothing can be done in these cases except to remove the cause of the affection as far as possible.