To the Editor We wish to discuss the effects of CBD and THC on visual function, which may influence driving but may not be detected by road-tracking tests as performed in the article by Dr Arkell and colleagues.1 A double-blind study reported that 15 mg of THC produced transient color discrimination impairment in the blue and red to yellow region of the color circle, while 8 mg of THC and placebo did not impair color discrimination ability.2 This transient color perception impairment may impair the development of numerous adaptations that individuals with congenital color defects use, such as memorization of the order of traffic signals. Another double-blind study found that 15 mg of THC impaired visual working memory, which may be associated with decreased task performance monitoring and increased mind wandering.3 Although there are several studies examining the effects of THC on vision, few studies have addressed CBD or compared THC with CBD in their effects on the human visual system. Only 1 double-blind study reported that a 5-mg sublingual dose of THC reduced intraocular pressure, while a 40-mg sublingual dose of CBD increased intraocular pressure.4 Future studies are warranted to examine the effects of CBD on the visual system.
Tseng P, Chen M, Liang C. Driving Impairment Following Vaporization of Cannabis. JAMA. 2021;325(12):1225–1226. doi:10.1001/jama.2021.0448
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