Whereas intraocular pressure is considered a major risk factor in glaucoma, growing evidence now indicates that ocular ischemia plays a major role too. By virtue of this and because many existing medications are able to interact with vasculature, altering ocular blood flow, it is essential that current and future medications for glaucoma be evaluated for their effect on ocular circulation. The authors review published papers examining the effect of topical and some systemic medications on ocular blood flow, focusing mostly on data from the human eye. The authors provide a comprehensive review on the effect of subclasses of medications (eg, carbonic anhydrase inhibitors, beta-blockers, alpha-adrenergic agonists, and prostaglandin analogues on optic nerve head, and on retinal, choroidal, and retrobulbar circulation. The various claims for enhancements or reduction of ocular circulation within each class of medication are reviewed and evaluated.