yeah, been looking for this, just found it

Just after passage of the Controlled Substances Act, the first new, modern medical use for the drug was discovered. In a strange bit of irony, a UCLA researcher began a study to develop methods by which the police could detect whether or not a person was intoxicated with marijuana. Instead, he inadvertently discovered marijuana's ability to reduce intra-ocular (internal eye) pressure and help patients with glaucoma. The researcher had intended to assess whether or not the pupil dilation that often accompanies marijuana smoking could be used by police to tell who was high and who was not. But he stumbled on a finding that saved many glaucoma patients from blindness, and led to a new area of medical research.