The consumption of cannabis or marijuana is on the rise among youngsters, with an element of 'cool' associated with its use. However, several studies have linked the use of the psychoactive substance to serious health conditions such as heart disease. A new study has added another potential side effect to the list—vision impairment.
According to researchers from the University of Granada (UGR), smoking cannabis can considerably affect vital visual functions such as the ability to focus, contrast sensitivity, visual acuity, glare sensitivity, and three-dimensional vision (stereopsis). "Smoking cannabis is associated with negative effects on visual function. Self-perceived visual quality after smoking cannabis could be related to impaired contrast sensitivity," wrote the authors.
A Global Indulgence
Cannabis is a generic term used to address numerous psychoactive concoctions made using three plants from the genus Cannabis— Cannabis indica, Cannabis sativa, and Cannabis ruderalis. According to the WHO, 2.5 percent of the world's population consumes cannabis products. In contrast, only 0.2 percent of the global population consumes opiates, and 0.2 percent abuse cocaine. In several countries, the production and use of cannabis are illegal.
The therapeutic effects of cannabis have been highlighted among sufferers of cancer and HIV. However, studies have also demonstrated that the prolonged use of cannabis can lead to loss of cognitive abilities such as memory, and worsen conditions such as schizophrenia. It can also cause respiratory illnesses such as lung inflammation, exacerbation of chronic bronchitis, and weakness of pulmonary defenses against infections. The list is endless.
"Surprisingly, despite all these consequences and the fact that it is an illegal drug, it is quite common to find misperceptions of the cannabis-use-associated risks, which could lead to an ever-increasing number of users," commented the authors.
Decrease In Visual Capacity
For the study, the authors analysed the effects of cannabis smoking on different visual parameters. It involved the exhaustive visual evaluation of 31 cannabis users (20 males and 11 females between the ages of 19 to 43). The participants were assessed under two conditions—when they had not partaken in cannabis substances and when they were under influence of the drug. The effects on vision after the consumption of the cannabis formed the crux of the assessment.
The researchers found that crucial visual functions such as glare sensitivity, contrast sensitivity, three-dimensional vision (stereopsis), and ability to focus, worsened considerably. Nevertheless, not all participants reported a decline in their vision after smoking cannabis.
While 30 percent of the volunteers reported no decrease in the quality of their vision, 65 percent stated that there was a slight worsening of their sight after smoking the drug. The authors pointed out that the visual parameter that may be most strongly connected to a user's perception of the visual effect is contrast sensitivity.
Need for Awareness
Nevertheless, the scientists noted that a negative effect was found on all the visual parameters that were evaluated. Most importantly, the study investigated the effects on some of the criteria for the very first time. According to the scientists, the participants also lacked awareness about the ill effects of marijuana on vision.
"Our results could help generate a better understanding of the visual changes related to cannabis use and their implications for everyday tasks, raising awareness among users of the risks involved consuming this drug," concluded the researchers.