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Effects of cannabis on visual function and self-perceived visual quality

Smoking cannabis can interfere with vision, but many people ignore it

A study by the University of Granada indicates that smoking cannabis significantly impairs key visual functions, such as visual acuity, contrast sensitivity, three-dimensional vision (stereopsis), ability to focus and focus. sensitivity to glare.

Smoking cannabis can impair vision, scientists warn: call for awareness

The use of cannabis or marijuana is on the rise among young people, with a “cool” element associated with its use. However, several studies have linked the consumption of this psychoactive substance to serious health problems, such as heart disease. A new study has added another potential side effect to the list: vision disorders.

According to researchers at the University of Granada (UGR), smoking cannabis can drastically affect vital visual functions such as the ability to focus, contrast sensitivity, visual acuity, sensitivity to glare, and vision. three-dimensional (stereopsis). “Smoking cannabis is associated with negative effects on visual function. Self-perceived visual quality after smoking cannabis could be linked to impaired contrast sensitivity, ”the authors write.

Cannabis is a generic term used to refer to many psychoactive concoctions made from three plants of the Cannabis genus: Cannabis indica, Cannabis sativa et C. According to the WHO, 2,5% of the world's population consume cannabis products. In contrast, only 0,2% of the world's population uses opiates, and 0,2% abuses cocaine. In several countries, the production and consumption of cannabis is illegal.

The therapeutic effects of cannabis have been shown in people suffering from cancer and HIV. However, studies have also shown that prolonged cannabis use can lead to loss of cognitive abilities, like memory, and worsen diseases like schizophrenia. It can also cause respiratory diseases such as inflammation of the lungs, exacerbation of chronic bronchitis, and weak lung defenses against infection. The list is endless.

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For the study, the authors analyzed the effects of cannabis use on different visual parameters. It involved a comprehensive visual assessment of 31 cannabis users (20 men and 11 women aged 19 to 43). Participants were assessed under two conditions: when they had not used cannabis-based substances and when they were under the influence of the drug. The crux of the assessment was the effects on vision after cannabis use.

The researchers found that crucial visual functions such as glare sensitivity, contrast sensitivity, three-dimensional vision (stereopsis), and the ability to concentrate, deteriorated dramatically. However, not all participants reported a drop in their vision after smoking cannabis.

While 30 percent of the volunteers reported no decrease in the quality of their vision, 65 percent said there was a slight worsening of their eyesight after smoking the drug. The authors pointed out that the visual parameter that may be most strongly related to a user's perception of the visual effect is contrast sensitivity.

Yet over 90% of consumers believe that cannabis use has no effect on their vision, or only a slight effect.

A group of researchers from the optics department of the University of Granada (UGR) has studied the effects of cannabis use on various visual parameters versus the effect that consumers themselves perceive to have an effect on their vision.

This study, led by Carolina Ortiz Herrera and Rosario González Anera, was published in the journal Scientific Reports. Its lead author, Sonia Ortiz Peregrina, explains that cannabis use is on the rise, despite being an illegal drug. According to the national survey on alcohol, drugs and other addictions in Spain 2019-2020, the consumption of cannabis at the national level has increased since 2011, with 37% of Spanish adults having used this drug at some point. About 10% used it in the past year.

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In this study, which obtained approval from the UGR's Human Research Ethics Committee (ref. 921 / CCEIH / 2019), a comprehensive visual test was performed on 31 cannabis users, both when 'they had not used any substance before and also when they were under the influence of the drug. The researchers also studied participants' perception of the visual effects of consuming this drug.

The results showed that, following consumption, visual aspects such as visual acuity, contrast sensitivity, three-dimensional vision (stereopsis), focusing ability and sensitivity to glare deteriorated significantly. . Despite this, not all subjects reported deterioration in their vision after smoking cannabis. Indeed, 30% said that their vision had not suffered at all, while 65% replied that it had only slightly deteriorated. The authors note that the visual parameter that may be most strongly related to users' perception of the visual effect is contrast sensitivity.

Just as with advancing age, sight diminishes ...

The study found a negative effect on all visual parameters assessed, with the effect of cannabis on some of the parameters being analyzed for the first time in this research. These findings, along with the lack of awareness that participants exhibited about the visual impairment caused by smoking cannabis, indicate the need for awareness campaigns, as this visual deterioration can pose a danger when performing. of daily tasks.

"Our results could help generate a better understanding of the visual changes associated with cannabis use and their implications for daily tasks, by raising awareness among users of the risks associated with the consumption of this drug," the researchers concluded.

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