Modern Glaucoma Surgery

3 / 22

© 2016, BSM Consulting 1
Modern Glaucoma Surgery
OVERVIEW
Many patients seen in today’s busy comprehensive or glaucoma specialty practice will require more than
medical therapy to achieve adequate intraocular pressure (IOP) control to preserve their vision.
Glaucoma surgery has evolved tremendously in the past twenty years. Trabeculectomy remains the gold
standard procedure, although recent major clinical trials have suggested that tube-shunt implantation may
be just as effective and perhaps even more so. In the past decade, several new procedures—many of
which involve the implantation of novel devices—have been developed and evaluated in clinical trials.
This course is designed to review the aspects of clinical evaluation and management of glaucoma during
the preoperative and postoperative periods for patients undergoing surgery for this potentially blinding
disease. In addition, we will review the common glaucoma surgical procedures, including an overview of
technique, success rates and complications, so that the ophthalmic technician has a good understanding
of the postoperative course of glaucoma surgery.
THE GLAUCOMAS
The glaucomas are a group of diseases that have in common a characteristic degeneration of the optic
nerve head with resulting loss of the peripheral visual field in typical glaucomatous patterns. Glaucoma
affects approximately 2% of Americans over age 40, and by 2020 there will be about 3.4 million people
with glaucoma in the US orldwide, more than 60 million people have glaucoma and this will grow to 80
million by 2020, with more than 11 million people blind from glaucoma in the world by that time
The most common form of glaucoma is primary open-angle glaucoma (POAG), which is typically seen in
older adults and is usually associated with elevated intraocular pressure (IOP). Previously, glaucoma and
elevated IOP were believed to be one and the same. More recently, epidemiologic studie nd clinical
trials have demonstrated that many patients with glaucoma do not have elevated IOP, and many people
with elevated IOP do not develop glaucoma Thus, elevated IOP is neither necessary nor sufficient to
explain the presence of glaucoma in an individual. Instead, elevated IOP is considered a risk factor for
glaucoma, as the likelihood of having glaucoma increases dramatically as IOP increases. Other risk
factors for glaucoma include black or Hispanic race, increasing age, family history, and a thin central
cornea Of these, only elevated IOP is modifiable, and IOP reduction remains the only proven therapy
for glaucoma. IOP reduction has been shown to effectively prevent the development of glaucom as well
as the progression of both normal-pressur and high-pressure glaucoma
IOP is determined by the balance of aqueous fluid production by the ciliary processes of the ciliary body
and the outflow of aqueous from the eye through both the trabecular meshwork and the poorly-
understood uveoscleral outflow pathway. Aqueous is made from blood circulating in blood vessels in the
ciliary body, and eventually drains out of the eye, into small veins, and back into the systemic circulation.
Aqueous that exits the eye through the trabecular meshwork drains first into Schlemm’s canal, then into
smaller collector channels that connect to the venous system of the conjunctiva. Aqueous exiting the eye
through the uveoscleral pathway is thought to drain into the venous system of the posterior segment.
In glaucoma, the trabecular meshwork (which is basically a drain) becomes clogged. In some cases, we
know why this happens. For instance, in pseudoexfoliation glaucoma, the pseudoexfoliation material
produced by ocular tissues that coats the anterior lens capsule also clogs the drain. In POAG, however,
we do not fully understand why the drain gets clogged or with what. As a result of the drain getting
clogged, the IOP becomes elevated, which leads to damage to the optic nerve and loss of the peripheral
visual field.
TREATMENT FOR GLAUCOMA
The goal of treatment for glaucoma is to lower the IOP. Several treatment modalities are available to
accomplish this, and they are typically applied in a stepwise fashion. Medications are the first line of
approach. Many different eye-drop medication classifications exist, and a few oral agents are available to
lower IOP. They work by either reducing aqueous production in the ciliary processes or by enhancing
aqueous outflow through either the trabecular meshwork or the uveoscleral pathway. Many patients will
require two or more medications to achieve a modest 20% IOP reduction Given that most glaucoma
treatment guidelines recommend at least a 25–30% IOP reduction (to a clearly defined target IOP), it is