Marijuana and vision--after ten years' use in Costa Rica.

Several tests of visual function were applied to an abstaining user (10 years or more) group and a nonuser group carefully preselected to be free of clinical signs of eye disease. The groups were matched on several criteria. The results show that all findings from both groups are within established limits of normalcy. Small differences and trends were found between the groups. These would have been undetected without large samples. Relative to the nonuser group, tests showed these user trends: increased basal lacrimation, increased intraocular pressure, increased photosensitivity, decreased dark adaptation, decreased color-match limits, and decreased Snellen acuity. These differences were associated with statistical probabilities, p=0.07 to p=0.001. There were no significant differences or clear trends between the user and nonuser groups in incidence of pathological fundus signs, conjunctival hyperemia, pterygia, or color-match midpoints.