Pupillary dynamics as a marker of acute cannabis inhalation.

Abstract

Introduction: Acute cannabis use has been found to affect pupil size and pupillary dynamics. Law enforcement may consider ocular changes in their examinations to determine drug impairment and the source, including from cannabis. A limited number of studies have used pupillometer technology to provide an objective measure of pupillary changes associated with cannabis use. The purpose of the study was to examine the sensitivity and specificity of pupil size and dynamics, measured with a pupillometer, associated with recent cannabis inhalation.

Methods: Participants (n = 126) completed a pupillometer assessment, using the NeurOptics PLR-3000 at three times. Of the 126 participants, 95 completed assessments at baseline, and at 40 min and 100 min following 15 min of ad libitum inhalation of self-provided cannabis flower or concentrate products. Thirty-one participants completed the same assessments without using cannabis. Sensitivity, specificity and accuracy were calculated for pupil size and dynamics measures associated with recent cannabis use versus no use, for both post-use time points. Least absolute shrinkage and selection operator models were used to identify the combination of ocular metrics that were most predictive and parsimonious.

Results: Following cannabis use, the pupillary measure with the highest area under the curve was percent change in pupil size, which decreased after cannabis use, with an area under the curve of 0.73 at 40 min and 0.75 at 100 min following cannabis use. Considering variables together in a least absolute shrinkage and selection operator model did not meaningfully improve prediction over individual measures.

Discussion: Consistent with some prior studies, we did not find that cannabis use was associated with substantial and consistent change in the maximum pupil size (measured in darkness) relative to controls. However, diminished pupil dynamics, such as constriction in response to light and recovery dilation, were more predictive of recent cannabis use, consistent with limited prior studies.

Conclusions: Pupillary dynamics, when measured with an objective test, may contribute to providing an indication of recent cannabis inhalation.