Caffeine is the most widely used drug in history, with more than 70% of New Zealanders consuming it daily in their coffee, tea, chocolate and caffeinated soft drinks - maybe more in Wellington where our coffee is so good! 

Interestingly there's emerging evidence that caffeine increases the eye's intra-ocular pressure (for a short period 1-2 hours after consumption).  Higher IOPs are associated with glaucoma, and the caffeine increase in IOP is worse in people with glaucoma, or who have a family history of glaucoma and seems to double their chance of developing glaucoma.  As they say "everything in moderation", more so for glaucoma risk people and their caffeine.