Cannabis impaired vision and driving ability, and the two were correlated
A driving simulator study found cannabis impaired visual acuity, contrast sensitivity, and stereoacuity, with the visual impairments directly correlated with worse driving performance.
Quick Facts
What This Study Found
In 20 young drivers, smoking cannabis significantly worsened visual acuity, contrast sensitivity, and stereoacuity (depth perception). Driving performance deteriorated, particularly lane-keeping. Crucially, the visual impairments and driving impairments were significantly correlated (r=0.504 for contrast sensitivity at near distances), providing the first evidence that cannabis-induced visual effects directly contribute to driving impairment.
Key Numbers
20 drivers; significant impairment in visual acuity, contrast sensitivity (p=0.004), near stereoacuity (p=0.013), and far stereoacuity; lane-keeping worsened; correlation r=0.504 between contrast sensitivity and driving.
How They Did This
Within-subjects study of 20 drivers and occasional cannabis users (mean age 23.3) evaluated at baseline and after smoking cannabis, assessing visual function and simulated driving performance.
Why This Research Matters
Previous cannabis-driving research focused on cognitive impairment. This is the first study showing that cannabis-induced visual changes themselves contribute to worse driving, adding a new dimension to understanding impairment.
The Bigger Picture
Cannabis impairs driving through multiple mechanisms: cognitive (attention, reaction time), motor (coordination), and now visual (acuity, depth perception). This multi-pathway impairment may explain why cannabis-impaired driving is more dangerous than some cognitive tests alone would predict.
What This Study Doesn't Tell Us
Small sample (n=20); mostly male; single cannabis smoking session; no dose-response assessment; simulated rather than real-world driving; participants were occasional users, not naive or heavy users.
Questions This Raises
- ?How long do the visual impairments last after cannabis use?
- ?Are regular users equally affected, or does tolerance develop for visual effects?
Trust & Context
- Key Stat:
- First study linking cannabis visual impairment directly to worse driving (r=0.504)
- Evidence Grade:
- Preliminary: small within-subjects study; novel finding but needs replication in larger samples.
- Study Age:
- Published 2020.
- Original Title:
- Effects of Smoking Cannabis on Visual Function and Driving Performance. A Driving-Simulator Based Study.
- Published In:
- International journal of environmental research and public health, 17(23) (2020)
- Authors:
- Ortiz-Peregrina, Sonia(3), Ortiz, Carolina(3), Castro-Torres, José J(2), Jiménez, José R, Anera, Rosario G
- Database ID:
- RTHC-02759
Evidence Hierarchy
Watches what happens naturally without intervening.
What do these levels mean? →Frequently Asked Questions
Does cannabis affect vision?
Yes. This study found cannabis significantly worsened visual acuity, contrast sensitivity, and depth perception (stereoacuity) in 20 young adults.
Is the visual impairment connected to driving problems?
Yes. This is the first study to show a direct correlation between cannabis-induced visual changes and driving impairment, suggesting that visual effects are a meaningful component of cannabis-impaired driving.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-02759APA
Ortiz-Peregrina, Sonia; Ortiz, Carolina; Castro-Torres, José J; Jiménez, José R; Anera, Rosario G. (2020). Effects of Smoking Cannabis on Visual Function and Driving Performance. A Driving-Simulator Based Study.. International journal of environmental research and public health, 17(23). https://doi.org/10.3390/ijerph17239033
MLA
Ortiz-Peregrina, Sonia, et al. "Effects of Smoking Cannabis on Visual Function and Driving Performance. A Driving-Simulator Based Study.." International journal of environmental research and public health, 2020. https://doi.org/10.3390/ijerph17239033
RethinkTHC
RethinkTHC Research Database. "Effects of Smoking Cannabis on Visual Function and Driving P..." RTHC-02759. Retrieved from https://rethinkthc.com/research/ortiz-peregrina-2020-effects-of-smoking-cannabis
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.