Filtration surgery (trabeculectomy) is performed when a piece of tissue in the drainage angle of the eye is removed, creating an opening. The opening is partially covered with a flap of tissue from the sclera and the conjunctiva. This new opening allows fluid to drain out of the eye, bypassing the clogged drainage channels of the trabecular meshwork.

As the fluid flows through the new drainage opening, the tissue over the opening rises to form a bubble, called a bleb. The bleb is located where the sclera joins the iris.

After surgery, antibiotics may be applied to the eye or your surgeon may inject antibiotics under the conjunctiva. After your surgery, the eyelid is usually taped shut, and an eye shield is placed over the eye.