Prostaglandins can lower intraocular pressure when they are applied topically to the eye. This pressure-lowering effect is mediated by enhancement of uveoscleral outflow. Human ciliary muscle has binding sites (receptors) for prostaglandins and the EP2 receptor subtype is the predominant prostanoid receptor found in this muscle. Prostaglandins are thought to bind to these receptors located on the ciliary muscle, induce its relaxation, and promote the uveoscleral outflow. It is important to know the receptor type involved in the pressure reduction to design a new drug with less adverse effect and more potency.