Modern Glaucoma Surgery

Modern Glaucoma Surgery

A procedure called deep sclerectomy is a hybrid of the two, allowing aqueous fluid to flow through a

small, thinned patch of cornea into a bleb-like space created within the sclera, from which it gains access

to Schlemm’s canal.

Canaloplasty is a procedure that lowers IOP by enhancing aqueous outflow through the trabecular

meshwork without truly bypassing the meshwork. A suture is threaded through Schlemm’s canal and tied

just tightly enough to pull the meshwork slightly inward—stretching it and presumably pulling open the

outflow channels to help aqueous flow through into Schlemm’s canal.

The procedures that lower IOP by reducing aqueous production by the ciliary processes are generally

only performed on eyes with end-stage glaucoma that have little functional vision and have failed all other

types of surgery. These procedures involve the use of either heat (by a laser) or cold (using a cryoprobe)

to destroy the tissue of the ciliary processes that manufacture aqueous. Because the ciliary processes

are permanently destroyed, there is a moderate risk of chronic hypotony with this procedure. These

procedures are typically performed trans-sclerally (through the sclera) without opening the eye. The

exception is endocyclophotocoagulation, which is performed using an endoprobe that is inserted into the

eye through a small incision in the peripheral cornea.

Each of these procedures will be discussed in more detail in the next section.

OVERVIEW OF GLAUCOMA SURGICAL PROCEDURES

All of the glaucoma surgical procedures are performed in an operating room of an ambulatory surgical

center or hospital and not in an in-office minor procedure room. The sterile environment is required

because the eye is opened during the procedures and instruments are inserted into it, conveying a small

but real risk of intraocular infection. Also, because there is significant manipulation of ocular tissues, local

anesthesia (more than topical anesthetic drops) usually is required. Every operation begins by confirming

the operative eye both by asking the patient and reviewing the signed consent form, then marking the

surgical site—in the case of eye surgery, this consists of making a mark (often an X) over the eye to be

operated on. This is to reduce the possibility of wrong-site surgery. Once the patient is in the operating

room, the eye and periorbital tissues are anesthetized (usually by injecting local anesthetic into the

periocular tissues of the orbit) to prevent pain, blinking, and eye movement. The eye is then sterilely

prepped using 5% povidone-iodine solution and draped to isolate the eyeball within the surgical field with

the eyelashes (a common source of bacterial contamination) sequestered by the drapes. A lid speculum

is then placed both to provide exposure of the surgical field and to prevent blinks in the case of sub-

optimal anesthesia.

BLEB-BASED PROCEDURES

Bleb-based procedures divert aqueous from inside the eye through a hole in the sclera into the

subconjunctival space. As a result, a “blister” of aqueous collects under the conjunctiva—this is called a

bleb. Once aqueous reaches the bleb, it is absorbed by conjunctival blood vessels and carried back into

the circulation. The common bleb-based procedures are trabeculectomy (with or without an Ex-PRESS

mini shunt), and tube-shunt procedures. These are discussed in more detail to follow.

Trabeculectomy

Trabeculectomy remains the standard glaucoma procedure for most surgeons. It was first described in

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and has changed relatively little since then. The goal of trabeculectomy is to bypass the clogged

trabecular meshwork and shunt aqueous into the subconjunctival bleb to be reabsorbed by conjunctival

blood vessels back into the systemic circulation.

Trabeculectomy involves a number of important steps. First, the conjunctiva is removed from its insertion

at the limbus for several clock hours (called a peritomy) to expose the sclera. Alternatively, an incision

can be made in the conjunctiva approximately 8–10 mm behind the limbus to expose the sclera. The

choice of location for the peritomy is based on the surgeon’s preference. Next, the surgeon dissects a

partial-thickness scleral flap hinged at the limbus, which is intentionally positioned over the trabecular

meshwork. A small piece of the trabecular meshwork (and its overlying sclera) is cut away under the flap,