 Latanoprost Xalatan is a prostaglandin F2 analogue which is believed to reduce IOP by increasing the outflow of aqueous humor. The retinal vascular effects of Latanoprost, however, remain unclear. While some studies have shown PGF2 to induce constriction in bovine isolated aqueous veins Nielsen 1996, other studies have been unable to demonstrate an effect on retrobulbar flow velocities Drance 1996. It is possible that vasoconstrictive properties of the drug may produce a negative impact on previously ischemic retinal tissue or at best no change. 