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

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.

Figure 1

Mean binocular contrast-sensitivity function for the baseline session and after smoking cannabis. Error bars indicate the SD and * is used when p < 0.05 (Wilcoxon-signed ranks test). cpd, cycles per degree.

Figure 2

Graph made with the Halo v1.0 software for one participant in the baseline session and after smoking cannabis. VDI value is included. (Pupil size was 5 mm for both sessions).

Figure 3

Group comparison for the different visual parameters in the baseline session and after smoking cannabis. * Indicates that the decline after smoking was significantly higher in group 2 than group 1.

Figure 4

Mean binocular contrast sensitivity function for groups 1 (left) and 2 (right) in the baseline session and after smoking cannabis. * indicates spatial frequencies for which there are significant differences (Wilcoxon test) and error bars indicate the SD. cpd, cycles per degree.