pupillometers

A pupillometer is an instrument designed to measure the size of the pupil, typically in millimeters, and, in many cases, the pupil’s response to light. Pupillometry, the measurement of pupil size and reactivity, can be performed with handheld devices or integrated into ophthalmic or research equipment. Modern pupillometers commonly use infrared illumination and a camera or sensor to detect the pupil against the surrounding iris.

Types and methods include infrared video pupillometers that automatically quantify pupil diameter, slit-lamp mounted devices used during eye examinations, and compact handheld units suitable for bedside measurements. Some devices measure static pupil size under a controlled lighting condition, while others assess dynamic reactivity, such as the pupillary light reflex, by delivering a light stimulus and recording latency and constriction velocity.

Applications span medicine, research, and sometimes psychology. In clinical settings, pupillometry supports assessment of neurological status and brainstem function, monitoring responses to medications or injury, and is used in anesthesia and critical care. In ophthalmology, it aids the evaluation of anisocoria and other pupil abnormalities. In psychology and human factors research, pupil dilation serves as a proxy for cognitive load, attention, or emotional arousal, often within broader eye-tracking studies.

Limitations include dependence on ambient lighting and ocular conditions, variability across devices and algorithms, the need for proper calibration, and potential artifacts from movement or eyelid interference.