A sclerostomy is a procedure in which the surgeon makes a small opening in the outer covering of the eye-ball to reduce intraocular pressure (IOP) in patients with open-angle glaucoma. It is classified as a type of glaucoma filtering surgery. The name of the surgery comes from the Greek word for "hard," which describes the tough white outer coat of the eyeball, and the Greek word for "cutting" or "incision."

Purpose

Sclerostomies are usually performed to reduce IOP in open-angle glaucoma patients who have not been helped by less invasive forms of treatment, specifically medications and laser surgery. In some cases—most commonly patients who are rapidly losing their vision or who cannot tolerate glaucoma medications—an ophthalmologist (eye specialist) may recommend a sclerostomy without trying other forms of treatment first.

From http://www.healthline.com/galecontent/sclerostomy