A study published in the Clinical Toxicology examined ocular measures as evidence of cannabis-induced impairment and found that pupil size is not predictive of acute cannabis exposure. The findings suggest that pupil size is not a reliable determinant of cannabis intoxication. Drug testing used by law enforcement officials commonly involves a variety of ocular measurements when a driver is suspected of cannabis intoxication.
Researchers affiliated with the University of Colorado performed pupillometer assessments on 126 participants, which involved using the NeurOptics PLR-3000 at three different times. 95 participants completed assessments at baseline, and then again at 40 minutes and 100 minutes following 15 minutes of consumption of cannabis flower or concentrate. Thirty-one participants completed the same assessments without cannabis use. The researchers calculated specificity, sensitivity, and accuracy for pupil size and dynamics measures associated with recent cannabis consumption versus no consumption. The research team also used least absolute shrinkage and selection operator models to identify the most predictive combination of ocular metrics.
The researchers observed that the pupillary measure with the highest area under the curve was percent change in pupil size. This measure decreased after cannabis use, with an area under the curve of 0.73 at 40 minutes and 0.75 at 100 minutes. The researchers did not observe a substantial or consistent difference in static pupil diameter relative to controls.
Although the findings were consistent with prior studies that did not find a strong association between cannabis use and substantial and consistent change in the maximum pupil size, they did find that diminished pupil dynamics (constriction in response to light and recovery dilation) were more predictive of recent cannabis use. Pupillary measures should be measured with an objective test if used to gauge recent cannabis inhalation.
Sources: Clinical Toxicology, NORML
