What is "pupillometry"

n. The measurement of the diameter of the pupil of the eye.

Pupillometry is the measurement of pupil diameter in psychology. This method established itself after its use in three seminal studies. The method examines humans (including infants) and animals. Pupillary responses occur from birth and are involuntary. Pupil dilation of 0.5 mm can occur when elicited by psychological stimuli.