Abstract
Cannabis is one of the most used drugs of abuse in the world. The objective of this study was to analyze the effects of smoking cannabis on vision and to relate these to those perceived by the user. Thirty-one cannabis users participated in this study. Visual function assessment was carried out in a baseline session as well as after smoking cannabis. We evaluated static visual acuity, contrast sensitivity, stereoacuity, accommodative response, straylight, night-vision disturbances (halos) and pupil size. The participants were also divided into two groups depending on whether they perceived their vision to have worsened after smoking cannabis. A logistic regression analysis was employed to identify which visual test could best predict self-perceived visual effects. The study found that smoking cannabis has significant adverse effects on all the visual parameters analyzed (p < 0.05). Self-perceived visual quality results revealed that about two thirds of the sample think that smoking cannabis impairs their vision. Contrast sensitivity, specifically for the spatial frequency 18 cpd, was identified as the only visual parameter significantly associated with self-perceived visual quality (Odds Ratio: 1.135; p = 0.040). Smoking cannabis is associated with negative effects on visual function. Self-perceived visual quality after smoking cannabis could be related to impaired contrast sensitivity.
Highlights
Cannabis is one of the most used drugs of abuse in the world
The paired t-test indicated lower binocular visual acuity and poorer mean contrast sensitivity after smoking cannabis, with this deterioration being significant at the spatial frequencies 0.75 cpd (z = − 2.724; p = 0.006) and 12 cpd (z = − 3.234; p = 0.001) (Table 1, Fig. 1)
Do you think that cannabis use affects your night vision, diminishing your ability to drive at night?
Summary
Cannabis is one of the most used drugs of abuse in the world. The objective of this study was to analyze the effects of smoking cannabis on vision and to relate these to those perceived by the user. Some decades ago certain studies addressed the effects of cannabis intoxication on visual p erception[11,12], but without explicitly controlling for confounding factors such as concomitant use of alcohol or tobacco, or the exact quantity consumed Their results indicating a deterioration in color vision[11], in static and dynamic visual acuity[13,14], in adaptation to darkness[14], and a longer glare-recovery time[12]. It has been demonstrated that there is reduced ocular sensitivity and intraocular pressure (IOP), conjunctival vasodilation and increased tear production[24] 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. We hypothesize that smoking cannabis could alter specific aspects of visual function such as visual acuity, stereoacuity, accommodative response and night-vision performance, and that some of these changes could determine the subjective perception of visual quality under acute intoxication
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