Biomarkers of recent drug use and intoxication have societal relevance, in that they are used
by law enforcement and other agencies to detect drug impairment. For instance, a breathalyzer
can quickly and accurately detect blood alcohol content (BAC) to indicate if a person is
under the influence of alcohol; however, there is currently no similar way to quickly detect
if a person is under the influence of cannabis. In light of increasing cannabis use, it is
important to define a quantitative, objective method of determining recent use and
intoxication.
The link between changes in eye characteristics (e.g. movement, pupil dilation) and cannabis
use is documented (Peragallo et al. 2013), but insufficiently characterized. Certain outcomes
of eye behavior are known to be affected by recent cannabis use (e.g. the eyes' ability to
converge on a target; Stapleton et al 1986), while findings are mixed regarding other
outcomes (e.g. the eyes' ability to smoothly follow a target; Fant et al. 1998). Thus, the
goal of this study is to identify a characteristic pattern of eye behavior, defined by
performance on a battery of four eye tasks, as a function of recent cannabis use (7% vs. 0%
THC).
Using 30 healthy cannabis users (15 men, 15 women), this study will be one of the first to
assess changes in eye behavior as a function of recent cannabis use within a quantified
virtual reality (VR) environment. This study will examine the effect of smoked cannabis (7%
vs. 0% THC) on individual eye movements, with the goal of defining the utility of the eyes as
potential objective indicators of cannabis use and intoxication. Four eye tests (nystagmus,
smooth pursuit, convergence, and pupillary light response; outlined below), which previous
literature has defined as effective in detecting recent drug use (including opioids and
alcohol; Murillo et al. 2004), have been compiled into a 5-minute task battery using a VR
headset environment equipped with high frequency infrared eye trackers (the HTC Vive with
Pupil Labs Tracking). This 5-minute VR battery of four eye tests will be administered prior
to cannabis consumption as a baseline, and then at 0, 15, 30, 45, 60, 75, 90, 105, 120, and
165 min after cannabis, with the goal of comparing baseline values to the ten post-cannabis
timepoints to detect changes in eye behavior as a function of cannabis intoxication. The
study will also utilize a battery of subjective-effects and mood visual analogue scales
(0-100 mm; e.g. 'Good Drug Effect') prior to the eye test battery at each timepoint, allowing
us to correlate each outcome of the eye tasks to subjectively reported cannabis impairment
and mood.
In addition to measuring eye behavior as a function of cannabis use, the training session of
this study will be used to also collect exploratory data on the relationship between pupil
dilation and experimental pain. Using Quantitative Sensory Testing (Medoc TSA-II NeuroSensory
Analyzer), thermal pain threshold and tolerance will be induced using a cold stimulus (4.0°C;
induced with a 30 x 30 mm Peltier thermode, which is 1.5" square metal applicator that is
connected to the TSA-II NeuroSensory Analyzer device and software, and produces an ongoing
cold sensation applied to the lower palm of the participant's non-dominant hand).
Participants will indicate first feelings of pain (pain threshold), and when the pain becomes
too much to bear (pain tolerance) by pressing a button on a controller connected to the
TSA-II. Throughout exposure to the cold stimulus, changes in pupil size to the patient's
subjectively reported pain latencies will be recorded.