Drug Discovery, Pharmaceuticals & Cannabis Testing
About Red Light/Green Light and Also Blue Light: Wavelength Specifi c Findings With Acute Marijuana Use
Dr Denise A. Valenti, IMMAD LLC,
deniseavalenti@gmail.com
While the popular television show of Squid Games made the horror and death of the game Red Light/Green Light seem real, we all knew the risk of any harm never really existed [1]. The same cannot be said of the potential harm and fatalities from not obeying Red Lights/Green Lights on real roads. And the harm is greater in cities now having legal adult use of marijuana. The rate of running red lights went up 18% in the city of Denver, Colorado USA, when legal adult use marijuana sales began [2]. The most recent records from 2022 show that in the USA there were 1,149 fatalities attributed to the running of red traffi c lights [3].
A potential explanation for these increasing fatalities at red lights are the dead spots, gaps in vision that occur with acute use of inhaled marijuana. Marijuana causes dysfunction of those visual pathways that rely on accurate input from dopaminergic receptors. When these are disrupted such as with the inhalation of marijuana, these pathways are dysfunctional. The pathways impacted are not the parvocellular visual paths processing colour and precise vision such as acuity, but the magnocellular pathways processing peripheral vision, contrast, motions, depth, and other non- acuity non-colour functions. That these pathways are signifi cantly impaired with inhaled marijuana was reported in 2018 [4]. The dysfunction reported demonstrates that a marijuana user would potentially have blind spots large enough to obscure the overhead Red Light/Green Light traffi c signals. Unlike for alcohol, the amount of marijuana in blood or saliva does not linearly relate to actual impairment. So objective tests of functions critical for safe driving are needed.
The data from the initial study reported research is superimposed on the windshield of a car in motion in the image below. A driver having recently used marijuana potentially cannot see the traffi c signal, let alone determine if it is Red Light/Green Light. The impact of marijuana within the eye’s retina is complex because every layer of the retina have cannabinoid/marijuana receptors [5, 6] and depending on which layer can be excitatory or inhibitory. Recent inhaled use of marijuana takes the dopamine out of the retina [7, 8] and reductions in dopamine result in visual impairment due to inhibition. This impairment can be measured using tests of the magnocellular pathway. One such test is the Frequency Doubling Technology (FDT) [9] visual fi eld which is commonly used to measure glaucoma. But the technology can detect dopamine depletion [10]. The science behind FDT is complex, but the test is simple. The instrument displays small striped squares of a fi xed temporal stripe fl ip but variable contrast. A person presses a button whenever they see stripes. The original FDT technology was in a tabletop test, but now systems with the test in simple virtual goggles are available. IMMAD, Impairment Measurement Marijuana and Driving [11] has demonstrated effi cacy of using visual reality goggles having the complex striped target for the
Figure 2: Intern Dr Xueling Zou tests an opportunistically dosed research participant with IMMAD.
detection of marijuana depletion of the retina induced blind spots [12]. Pictured is a research participant after having self dosed under an IRB approved opportunistic dosing protocol. Part of the research involved real car, closed road driving. This was funded by the National Institute of Justice [13]. This research discussed was supported by Award No. 15PNIJ-22-GG-04417-RESS awarded by the National Institute of Justice, Offi ce of Justice Programs, US Department of Justice. The opinions, fi ndings, and conclusions or recommendations expressed in this program are those of the author and do not necessarily refl ect those of the Department of Justice.
The data on impairment obtained from the IMMAD technology after marijuana use shows a relationship to the retinal location of a subclasses of retinal ganglion cells, the melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGC) [14]. The function of these cells include contrast sensitivity perception, depth perception, and motion perception. Other research has found decreases in contrast sensitivity perception with acute marijuana use [15].
The ipRGC are responsible for what is referred to as the post illumination pupil response (PIPR). PIPR is the sustained constriction of the pupil when pupil responses are considered normal. Part of a drug evaluation performed by law enforcement roadside is using a light to determine pupil response and when marijuana is suspected to be causing impairment to drive they are looking for a specifi c pupil re dilation with continued illumination of the pupil [16]. The dysfunction in sustained pupil constriction is referred to as rebound dilation. The pupil initially constricts with direct illumination but then has a partial dilation with continued direct illumination with marijuana use. The ipRGC are temporarily inhibited with acute marijuana use and the failure to respond are the contributing factors in the observation of rebound dilation [14].
Figure 1: IMMAD identifi ed signifi cant visual fi eld losses with inhaled marijuana use. These are demonstrated by the red squares displayed against the driver’s side windshield.
We discussed Red Light/Green Light and now we are going to discuss Blue Light. Blue light is the primary driver of both direct and consensual PIPR response under normal circumstances, absent the use of marijuana [17-19]. To observe the marijuana induced rebound dilation the light source, penlight needs to have blue wavelengths. Because the observation of the cannabis induced dysfunction of rebound dilation is chromatically driven. It is observed with illumination sources having blue in the wavelength spectrum.
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