pupillometer

A pupillometer is an instrument used to measure the diameter of the pupil and, in some models, to assess the pupillary light reflex and dynamic pupil responses. Modern devices typically use infrared illumination and a camera to capture the eye, with software that computes pupil size in millimeters. Simpler, manual devices such as rulers or calipers are also used for quick estimates.

Pupillometers can be categorized as static or dynamic. Static pupillometers measure pupil size at rest, while dynamic or reactive pupillometers monitor changes in size over time in response to light or other stimuli. Some systems quantify additional parameters such as constriction velocity, latency, and dilation after stimulus offset.

Common uses include ophthalmology and optometry to evaluate pupil abnormalities, anisocoria, and drug effects on the pupil; neurology and critical care to monitor neurologic status and autonomic function; and anesthesia to assist monitoring of sedation depth. In research, pupillometry is employed to study cognitive load, arousal, and reflex pathways.

Limitations and accuracy considerations include sensitivity to ambient lighting, gaze direction, eyelid position, iris color, and corneal reflections. Calibration and standardized protocols improve inter-device comparability, and manual measurements are prone to observer error. The field is evolving toward automated, noninvasive infrared pupillometry with standardized reporting.

Historically, pupillometers emerged from simple manual tools in the 19th and early 20th centuries and evolved through photographic and electronic sensing methods to contemporary digital devices that enable rapid, repeatable measurements in clinical and research settings.