A Custom-made Pupillometer System for Characterizing Pupillary Light Response

Abstract

Objectives: This paper presents the design and construction of a viable pupillometer system and demonstrates its merits with extensivevalidation tests.Materials and Methods: A web camera was modified by removing its infrared filter and mounted on a chin rest. Light emittingdiodes (LEDs) operating at infrared and visible spectra were integrated to provide background and light stimulus, respectively. The LEDswere controlled by a microprocessor board. Stimulation was presented using a periodic paradigm with variable period and duty cycle.Videos of both pupils were recorded at 30 frames/second and processed offline using software developed in-house. The overall system wasvalidated with data gathered from individuals with healthy vision under different stimulation paradigms. Temporal variations in pupilsize were determined and analyzed statistically.Results: The analysis revealed that the pupil sizes were accurately measured from the video frames provided that reflections from bothinfrared and visible lights remain outside the pupil. The system achieved moderate to excellent repeatability scores (87.8 and 86.8% forshort 1 second and long 2 second pulses, respectively), which demonstrated its effectiveness and confirmed that it can be used reliablyas a pupillometer.Conclusion: The proposed pupillometer system produces useful, quantitative data characterizing pupillary light response. However,further development and implementation are needed to potentially turn it into a low-cost alternative for other studies involving theautonomic nervous system, cognitive function, drug metabolism, pain response, psychology, fatigue, and sleep disorders.