This is a hyperosmotic (lots of salt) eye drop that is used in cases of corneal edema. The cornea (the clear structure that makes up the front of our eye) is clear because it is relatively dry. With certain conditions such as Fuchs’ dystrophy or after cataract surgery, the cornea can become wet and cloudy. Muro drops and ointments can be used to dry the eye out. Because this drop has a high salt content, water is attracted to it and the drop literally sucks or pulls water out of the cornea. Muro isn’t really a drug so you don’t necessarily need a prescription for it. However, pharmacists keep it behind the counter and so a prescription is usually written anyway.