SCLEROSTOMY GLAUCOMA SURGERY

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."

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.

As of 2003, glaucoma is not considered a single disease but rather a group of diseases characterized by three major characteristics: elevated intraocular pressure (IOP) caused by an overproduction of aqueous humor in the eye or by resistance to the normal outflow of fluid; atrophy of the optic nerve; and a resultant loss of visual field. A sclerostomy works to reduce the IOP by improving the outflow of aqueous humor. Between 80% and 90% of aqueous humor leaves the eye through the trabecular meshwork while the remaining 10–20% passes through the ciliary muscle bundles. A sclerostomy allows the fluid to collect under the conjunctiva, which is the thin membrane lining the eyelids, to form a filtration bleb

Demographics
In 1995, the World Health Organization (WHO) reported that over five million people around the world have lost their sight due to complications of glaucoma; about 120,000 Americans are blind as a result of glaucoma. According to the National Eye Institute (NEI), nearly three million people in the United States have the disorder; however, nearly half are unaware that they have it. Primary open-angle glaucoma (POAG) accounts for 60–70% of cases. “Primary” means that the glaucoma is not associated with a tumor, injury to the eye, or other eye disorder. Although glaucoma can occur at any age, it is most common in adults over 35. One major study reported that less than 1% of the United States population between 60 and 64 suffer from POAG. The rate rises to 1.3% for persons between 70 and 74, however, and rises again to 3% for persons between 80 and 84.

With regard to race, African-Americans are four times as likely to develop glaucoma as Caucasians, and six to eight times more likely to lose their sight to the disease. African Americans also develop glaucoma at earlier ages; while everyone over age 60 is at increased risk for POAG, the risk for African Americans rises sharply after age 40. A 2001 study reported that the rate for Mexican Americans lies between the rate of POAG in African Americans and that in Caucasians. Mexican Americans, however, are more likely to suffer from undiagnosed glaucoma—62% as compared to 50% for other races and ethnic groups in the United States. In addition, the rate of POAG in Mexican Americans was found to rise rapidly after age 65; in the older age groups, it approaches the rates reported for African Americans. Among Caucasians, people of Scandinavian, Irish, or Russian ancestry are at higher risk of glaucoma than people from other ethnic groups.

The question of a sex ratio in open-angle glaucoma is debated. Three studies done in the United States between 1991 and 1996 reported that the male:female ratio for open-angle glaucoma is about 1:1. Three other studies carried out in the United States, Barbados, and the Netherlands, however, found that the male:female ratio was almost 2:1. A 2002 study from western Africa reported a male:female ratio of 2.26:1. It appears that further research is needed in this area.

Description
Most sclerostomies are performed as outpatient procedures under local anesthesia. In some cases the patient may be given an intravenous sedative to help him or her relax before the procedure.

Conventional sclerostomy
After the patient has been sedated, the surgeon injects a local anesthetic into the area around the eye as well as a medication to prevent eye movement. Using very small instruments with the help of a microscope, the surgeon makes a tiny hole in the sclera as a passageway for aqueous humor. Some surgeons use an erbium YAG laser to create the hole. Most surgeons apply an antimetabolite drug during the procedure to minimize the risk that the new drainage channel will be closed by tissue regrowth. The most common antimetabolites that are used are mitomycin and 5-fluouracil. After the surgery, the aqueous humor begins to flow through the sclerostomy hole and forms a small blisterlike structure on the upper surface of the eye. This structure is known as a bleb or filtration bleb, and is covered by the eyelid. The bleb allows the aqueous humor to leave the eye in a controlled fashion.

Enzymatic sclerostomy
A newer technique that was first described in 2002 is enzymatic sclerostomy, which was developed at the Weizmann Institute of Science in Israel. In enzymatic sclerostomy, the surgeon applies an enzyme called collagenase to the eye to increase the release of aqueous humor. The collagenase is applied through an applicator that is attached to the eye with tissue glue for 22–24 hours and then removed. According to the researchers, the procedure reduced the intraocular pressure in all patients immediately following the procedure and in 80% of the subjects at one-year follow-up. None of the patients developed systemic complications. Enzymatic sclerostomy is considered experimental as of mid-2003.