Smoking Cannabis Significantly Impairs Vision

Article: Smoking cannabis significantly impairs vision but many users are unaware of it
Source: University of Granada (Spain)
Published: April 12, 2021 

Smoking cannabis worsened visual quality
in all assessments evaluated

Researchers in Spain conducted a study examining the effects of cannabis (marijuana) use on vision and the awareness of visual impairment among cannabis users. The authors stress that in Spain, cannabis use has increased within the past decade despite this drug of abuse being illegal. Thirty-one cannabis users participated in the study. In particular, the researchers evaluated visual function in assessments of static visual acuity, contrast sensitivity, stereoacuity, accommodative response, glare sensitivity, and pupil size at baseline and after smoking cannabis . The authors report, "The study found that smoking cannabis has significant adverse effects on all the visual parameters analyzed." Despite this, survey of the participants revealed that 30% of the cannabis users self-reported that their quality of vision did not suffer at all, while 65% responded that their vision worsened only slightly. Among those participants who did perceive a decrease in visual quality, only contrast sensitivity (specifically at the highest spatial frequency tested) was identified. The researchers state, "These results, together with the lack of awareness that the participants presented about the visual impairment caused by smoking cannabis, indicate the need to carry out awareness-raising campaigns, as this visual deterioration can pose a danger when performing everyday tasks."

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Ortiz-Peregrina S, Ortiz C, Casares-López M, et al. “Effects of cannabis on visual function and self-perceived visual quality.” Scientific Reports.  11:1655. 18 January 2021. https://doi.org/10.1038/s41598-021-81070-5