Smoking causes the poisonous substances from the tobacco to enter your blood. This in turn increases chances of blood clots, raised blood pressure and heart rate, narrows your arteries and reduces the level of oxygen in your blood, which is needed to keep the body healthy. These changes go on to cause many serious health conditions.
There is no evidence that smoking itself is a risk factor for glaucomatous damage but older smokers also have a higher risk of developing increased eye pressure (intraocular pressure) as compared to non-smokers.
If you have dry eye disease, smoking will cause your eyes to sting and feel scratchy, causing your eyes to water and feel more uncomfortable.
Some eye conditions (obstruction of retinal vessels, maculopathy, cataracts, etc.) are much more common in smokers and occur at an earlier age than in non-smokers.
Even though marijuana does decrease the intraocular pressure, its medical use has not yet been investigated to the extent that it can be recommended as a therapeutic drug. Very few controlled studies have been performed; the advantages and disadvantages of long-term treatment need to be rigorously assessed.