Modern Glaucoma Surgery

Modern Glaucoma Surgery

likely that most patients will require multiple medications to achieve adequate IOP control. Patients whose

glaucoma cannot be controlled with medications—or who cannot faithfully use medications or prefer not

to use them—can undergo a laser procedure called trabeculoplasty. This procedure effectively lowers

IOP for many patients by unclogging the drain, although its effect tends to wear off over time as the drain

reclogs, requiring the need for a repeat trabeculoplasty one or more years later

. 11

For difficult cases of

glaucoma that do not respond well to medical or laser therapy, surgical intervention may be necessary.

The progression from medications to laser to surgery

reflects the increasing risk with each progressive

step. While surgery can lower IOP more effectively

than medications or laser therapy, it also has more

serious potential complications. Therefore, the

decision to proceed to glaucoma surgery should be

based on a careful assessment of the patient and a

risk/benefit analysis that justifies the potential risks of

surgery in order to prevent vision loss. Several

different events can justify the need for glaucoma

surgery (

Table 1

). One common reason that

glaucoma surgery is necessary is that the IOP

remains above the target IOP despite the use of all

tolerated medications and the prior application of laser therapy. In this case, every effort should be made

to determine whether the patient is truly using the medications as prescribed. In some instances, poor

adherence to therapy can be identified and addressed and surgery avoided. Another common justification

for surgery is the progression of damage to the optic nerve head or the visual field. Particularly in the

case of visual field progression, any new change should be confirmed on at least one additional visual

field test before proceeding with surgery, as false-positive progression on visual field testing is not

uncommo

n. 12

A less common reason for glaucoma surgery is intolerance to topical medications, which

can be related to an allergy to the preservatives in the medications. Similarly, some patients cannot self-

dose their medications due to physical limitations (e.g., tremor or arthritis) or cognitive limitations (e.g.,

dementia).

PRINCIPLES OF GLAUCOMA SURGERY

The goal of all glaucoma surgical procedures (

Table 2

) is to lower IOP. The vast majority of glaucoma

surgeries lower IOP by increasing outflow, generally by means of bypassing the clogged trabecular

meshwork.

The most commonly performed procedures involve

creation of a full-thickness trans-scleral bypass,

including trabeculectomy, the Ex-Press mini shunt,

and the tube-shunt. These procedures allow

aqueous fluid to drain into the subconjunctival

space, where it is eventually reabsorbed into the

bloodstream through the conjunctival blood vessels.

All three of these procedures require the creation of

a permanent reservoir of aqueous under the

conjunctiva, called a bleb.

It is also possible to bypass just the trabecular

meshwork without involving other structures of the

eye wall, as is the case with trabecular ablation

using the TrabecTome and stenting the meshwork

using the iStent. These procedures facilitate

aqueous flowing from the anterior chamber directly

into Schlemm’s canal, and thus do not result in the

formation of a bleb.

TABLE 1

Events Justifying Glaucoma Surgery in Patients

Treated With Medical ± Laser Therapy

•

IOP determined to be too high

•

Progression of the visual field

•

Progression of the optic nerve

•

Intolerance to glaucoma medications

•

Inability to self-dose glaucoma medications

TABLE 2

GLAUCOMA SURGICAL PROCEDURES

Bleb-based procedures

•

Trabeculectomy

•

Ex-Press

•

Tube-shunt

Trabecular bypass procedures

•

Trabecular ablation (TrabecTome)

•

Trabecular stenting (iStent)

Other outflow procedures

•

Deep sclerectomy ± viscocanalostomy

•

Canaloplasty

Cilioablation procedures

•

Laser

•

Cryotherapy