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Marijuana and driving: Hitting a pothole


Denise Valenti, OD, advises on why driving under the influence of marijuana is not without visual consequences.

Reviewed by Denise Valenti, OD.

Denise Valenti, OD

Denise Valenti, OD

Tunnel vision is an often-mentioned effect of marijuana both by users of the substance, as well as the National Highway Traffic Safety Administration. Despite the fact that educational campaigns also reported tunnel vision, only 1 study has been conducted on humans and peripheral vision.1

In the US, 16 states do not require visual field testing for driver’s licenses, the other 34 states have a binocular horizontal visual field requirement. Fifteen states stipulate a visual field of 140 degrees, and 19 states from 105 to 130 degrees; Maine requires 150 degrees.

Kentucky is the only state that requires vertical visual field testing, i.e., 25 degrees above and below the fixation point. All provinces in Canada require intact vertical fields.

In contrast to that study, 2 studies reported that marijuana may improve night vision.2,3

In the literature: no safety in numbers

An animal study found that tadpoles could see better in extremely low light, when cannabinoid receptors were stimulated.4 In the study, all tadpoles were observed swimming toward the light.

Humans have numerous cannabinoid receptors in the retina, CB1 and CB2. The latter is in the cone and rod photoreceptors, horizontal cells, some amacrine cells, and bipolar and ganglion cells.

When tested in mice5 in the dark, a-waves slower in mice genetically engineered not to have CB2, but in those without CB1, no change was seen. Under photopic conditions, the b-wave in mice without CB2 required more light adaptation.

The authors concluded that CB1 and CB2 receptors could have different roles in visual processing.

Investigators found that when children aged 4 to 5 years were exposed to alcohol and marijuana prenatally, the global motion perception improved with exposure to marijuana, and decreased with alcohol. However, the increase may negatively affect other functions.

The alarming, inaccurate take-home message here as a result of these studies: it is considered safe to drive after marijuana use by many, even while driving.

As a result, marijuana has been detected in markedly higher percentages of drivers, and often with deadly consequences. The rate of marijuana impaired driving fatalities doubled in those states with legal adult use marijuana, according to the American Automobile Association.

Effects on eyes

The following snippets highlight the effects of marijuana use on the eyes:

  • A mouse prenatal study found that the animals had thinner retinas when exposed to marijuana.7
  • While the peripheral vision is enhanced, the central vision is suppressed.
  • The recovery time after exposure to bright light is significantly longer after marijuana use.8
  • Marijuana produced dose-dependent pupillary constriction in low photopic light.8
  • Dysfunctions in dynamic acuity occurred with 8- and 15-mg doses of marijuana.8
  • Color vision is impaired with marijuana use.9-11
  • The substance impairs retinal ganglion cell function.12
  • Acute use of marijuana changes the retinal response.12
  • Use of marijuana at an early age results in dysfunctional contrast sensitivity at low spatial frequencies. Electroretinography recorded a reduced response to coherent, incoherent, and static motion.13
  • Marijuana inhibits dopamine production in the retina.14
  • In sporadic users, the following measures were reduced: binocular acuities, contrast sensitivity, and stereo near and distance; these drivers had difficulty keeping their cars in the lanes.15
  • Microsaccades are suppressed.
“If a driver cannot see accurately, they cannot drive safely," Valenti said.

"More research is needed so that we can fully understand how marijuana impacts driving with acute recent use.

Further given that studies show permanent reductions in those brain regions that process vision when initiation of marijuana occurs with early age, adolescent use, that area of research is urgent.

On the other end of the age spectrum, cannabis use in moderate doses may actually be beneficial to the aging brain. "There is so little we do not know. But we do know that recent use of marijuana impairs functions critical for safe driving. Enjoy legal adult use marijuana responsibly. Do not drive,” Valenti concluded.

  1. Moskowitz H, Sharma S, McGlothlin W. Effect of marihuana upon peripheral vision as a function of the information processing demands in central vision. Percept Mot Skills 1972;35875-82; doi: 10.2466/pms.1972.35.3.875.
  2. Russo EB, Merzouki A, Meas JM, et al. Cannabis improves night vision: a case study of dark adaptometry and scotopic sensitivity in kif smokers of the Rif mountains of northern Morocco. J Ethnopharmacol 2004;93:99-104.
  3. Merzouki A, Mesa JM. Concerning kif, a Cannabis sativa L. preparation smoked in the Rif mountains of northern Morocco. J Ethnopharmacol 2002;8:403-6.
  4. https://elifesciences.org/con tent/5/e15932
  5. Cécyre B, Zabouri N, Huppé-Gourgues F, et al. Roles of cannabinoid receptors type 1 and 2 on the retinal function of adult mice. Invest Ophthalmol Vis Sci 2013;54:8079-90. doi:10.1167/iovs.13-12514
  6. Chakraborty A, Anstice NS, Jacobs RJ, et al. Prenatal exposure to recreational drugs affects global motion perception in preschool children. Sci Rep 2015 Nov 19;5:16921. 
  7. Adams AJ, Brown B, Haegerstrom-Portnoy G, et al. Marijuana, alcohol, and combined drug effects on the time course of glare recovery. Psychopharmacology (Berl) 1978; ;56:81-6.
  8. Adams AJ, Brown B, Haegerstrom-Portnoy G, et al. Marijuana, alcohol, and combined drug effects on the time course of glare recovery. Psychopharmacology 1978; 56:81–6.
  9. Dawson WW, Jimenez-Antillon CF, Perez JM, Zeskind J. Marijuana and vision—after ten years’ use in Costa Rica. Invest Ophthalmol Vis Sci 1977;16:689-99.
  10. Adams AJ, Brown B, Flom C, et al. Alcohol and marijuana effects of static visual acuity. J Optom Physiol Opt 1975;52:729-35.
  11. Zantut PRA, Veras MM, Benevenutto SGM, et al.. Lasting effects of prenatal exposure to Cannabis in the retina of the offspring: an experimental study in mice. Int J Retina Vitreous. 2021;30;7:45.
  12. Schwitzer T, Schwan R, Albuisson E, et al. Association between regular cannabis use and ganglion cell dysfunction. JAMA Ophthalmol 2017; 135: 54-60.
  13. Busquets-Garcia A, Gomis-González M, Salgado-Mendialdúa V, et al. Hippocampal protein kinase C signaling mediates the short-term memory impairment induced by Delta9-tetrahydrocannabinol. Neuropsychopharmacology2018;43:1021-31.
  14. Yazilla http://www.ncbi.nlm.nih.gov/pubmed/18725316
  15. Ortiz-Peregrina S, Ortiz C, Castro-Torres JJ, et al. et al. Effects of smoking cannabis on visual function and driving performance. a driving-simulator based study. Int J Environ Res Public Health 2020;17:9033.
Denise A. Valenti OD, FAAO: deniseavalenti@gmail.com
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