Marijuana definitely decreases intraocular pressure, but there's no widespread agreement over whether that's the only cause of glaucoma.
Temporarily, and the reduced blood pressure may also cause harm in Glaucoma patients, effectively nulling the effects of reduced pressure. And it only lasts about 3-5 hours, most people say, so I'd have to pretty much be continuously blazing in order to keep it reduced, rather minimally. I don't like smoking pot, I've done it before. I don't like smoking anything, so I'd only ever give this a shot during something like spring break and only if I have a vaporizer or edibles.