glaucoma management
The Basics of Glaucoma Surgery
Before you recommend a surgical consultation for glaucoma, arm yourself with information to educate your patients.
BY DEEPAK GUPTA, O.D., Stamford, Conn.

With the continuing advances in drugs, we can successfully manage many glaucoma patients with medical therapy. However, some will still require us to refer them for surgery to preserve their vision.

Before a surgical consultation, patients will expect you to answer questions about the procedure. In the next few pages I'll highlight some of the surgical procedures used to treat and manage glaucoma.

The ALT alternative

Argon laser trabeculoplasty (ALT) is one of the most commonly performed glaucoma surgeries. The goal is to create small laser burns around the trabecular meshwork to increase aqueous fluid outflow. In most cases the surgeon does half the angle (180 degrees), reserving the other half for future treatment, if necessary. It typically takes four to six weeks for the full effect of ALT to manifest.

The Glaucoma Laser Trial established the efficacy of ALT as a primary treatment for lowering intraocular pressure (IOP) in open-angle glaucoma. Still, many O.D.s (myself included) consider ALT too aggressive as a primary treatment. I prefer ALT when medications fail to adequately control IOP, or where a patient demonstrates a pattern of noncompliance with medications.

ALT is contraindicated in any patient who has complete angle closure or in whom hazy media prevent sufficient visualization of the angle structures. Experts may also contraindicate ALT in one eye if a serious complication from laser treatment occurred in the fellow eye. Secondary open-angle glaucomas, such as the inflammatory glaucomas, generally don't respond well to laser trabeculoplasty.

Patients older than 40 typically respond better than do younger patients. Race doesn't appear to impact the short-term efficacy, but long-term success is lower among black patients.

In general, ALT controls IOP in 80% of eyes at one year, 50% at five years and 30% at 10 years. Thus, half of your patients will need additional therapy after five years and 70% will need supplemental treatment after 10 years. Coagulative damage to the trabecular meshwork from ALT may limit the efficacy of further therapy.

Complications from ALT are relatively mild and transient. IOP typically rises less than 5mmHg after ALT, reaching its peak at three hours and resolving within 24 hours. Some patients demonstrate larger, less transient IOP spikes that cause optic nerve damage and visual field loss.

The Glaucoma Laser Trial found that the strongest risk factor for IOP increase after ALT was moderate or heavy pigmentation of the trabecular meshwork. This risk of IOP spikes can be decreased by instilling one drop of an alpha adrenergic agonist one hour before and immediately after the procedure. Ocular pain is usually minimal with laser trabeculoplasty; most patients require only topical anesthesia for the procedure.

Consider the SLT option

Unlike ALT, which targets all cells (pigmented and nonpigmented), selective laser trabeculoplasty (SLT) selectively targets melanin within the trabecular meshwork cells using a Q-switched frequency-doubled Nd:YAG laser. Because of this selective targeting of the laser energy, SLT doesn't cause thermal damage to surrounding tissue and the subsequent scarring to the trabecular meshwork that occurs in ALT.

Indications and contraindications for SLT are the same as those for ALT. A randomized study of patients who underwent unsuccessful ALT found that IOP reduction was better after SLT than it was after repeat ALT. Some 70% of the patients had an IOP reduction of at least 3mmHg and an average IOP reduction of 5mmHg to 6mmHg. Complications of SLT are similar to ALT, but with a reduced incidence.

Filtering surgery

Filtering surgery, or trabeculectomy, is the most common non-laser surgical procedure for managing glaucoma. The surgeon removes a piece of the cornea or sclera to create an alternative pathway for aqueous fluid to leave the anterior chamber. The fluid pools in a reservoir, or bleb, under the eyelid, where the episcleral venous drainage gradually absorbs it. This increased outflow facility reduces IOP.

Surgeons usually order a trabeculectomy when both medical and laser therapy fail to achieve target IOP. It's most effective for cases of uncontrolled primary open-angle glaucoma, closed-angle glaucoma, exfoliation syndrome and pigmentary glaucoma.

The secondary glaucomas (neovascular, uveitic, developmental, traumatic, aphakic and congenital) generally have a much poorer prognosis with filtering surgery and may require other treatment modalities, which I'll describe later. Even so, after medicine and laser surgery have failed as a first option, a trabeculectomy is still the initial surgical intervention attempted in these cases.

The five-year Collaborative Initial Glaucoma Treatment Study (CIGTS) found that medication and filtering surgery are both effective for short-term primary treatment in open-angle glaucoma. However, in the United States trabeculectomy is generally reserved for patients who fail to maintain adequate IOP while on maximum drug therapy.

Trabeculectomy, alone or with medical therapy, has a success rate approaching 95% at two years. The long-term results are not as optimal. After five years, 60% to 80% of patients may require additional therapy or a repeat procedure.

In the first two weeks post-op, monitor the bleb for leaks and vascular integrity. Also, check the anterior chamber for proper depth and for cells and flare, and examine the posterior pole for choroidal effusion. The most common problem after trabeculectomy is shallowing of the anterior chamber. Wound leak or excessive filtration usually causes this. You can sometimes manage bleb leaks conservatively; in other instances, surgical repair is necessary. Fortunately, sustained severe shallowing is rare and many chambers re-form spontaneously.

Early bleb failure is also possible and may require one or more management techniques. Other potential complications of trabeculectomy include choroidal effusions, late bleb failure and formation of a Tenon cyst. Any of these warrants a referral back to the surgeon for an assessment.

Nonpenetrating surgeries

Nonpenetrating filtering surgery is a relatively new procedure similar to trabeculectomy, except that the surgeon creates a thin membrane under the scleral flap without penetrating the eye. Indications are the same as those for a trabeculectomy. The following are the two types of nonpenetrating surgeries:

1. Bleb-forming surgeries, which include ab externo trabeculectomy (AET), where the surgeon excises the inner wall of Schlemm's canal and the juxtacanalicular trabecula to create a thin membrane; and deep sclerectomy, where the surgeon removes corneal stroma behind the anterior trabecula and Descemet's membrane.

2. Viscocanalostomy. The surgeon removes a deep piece of scleral tissue and part of the trabecular meshwork and anterior wall of Schlemm's canal. This allows aqueous fluid to bypass the trabecular meshwork and to percolate through an intact Descemet's window.

Most studies also show that nonpenetrating surgery has fewer complications than penetrating procedures and a lower risk of post-op infection and less need for antimetabolites. However, studies show that nonpenetrating deep sclerectomy is less effective than trabeculectomy in lowering IOP. Some additional disadvantages of deep sclerectomy include elevated IOP for up to one month post-op; the procedure takes up to three hours to perform; and it requires a large scleral flap, leaving less superior conjunctiva available in the event of additional surgeries.

Hypotony is common during the first several days after deep sclerectomy. Late rupture of the newly created membrane also occurs in nonpenetrating surgery. If this occurs, send the patient back to the surgeon for treatment.

Tube shunts

An aqueous shunt may benefit the patient who has significant scarring from previous glaucoma surgeries or from glaucoma that is resistant to other forms of treatment. In this procedure, the surgeon routes a small plastic tube from the anterior chamber of the eye to a plate inserted 10 mm behind the limbus. Aqueous fluid then drains through the tube to the top of the plate. There, the ocular blood vessels absorb the fluid, thus lowering IOP.

Tube shunts are useful in such situations as inflammatory glaucoma, angle-closure glaucoma and certain cases of chronic open-angle glaucoma. Elevated IOP in inflammatory glaucoma that fails to respond to medical therapy usually shows a good response to shunts. Shunts are often used when filtering surgery fails to adequately control IOP.

Shunt procedures generally don't yield low-end IOPs. Many researchers define a successful procedure as one that yields an end IOP below 21mm Hg, which may or may not be enough to stop the progression of glaucoma.

Hypotony, with or without associated choroidal effusions, is the most common early postoperative complication of shunt implantation. Small choroidal effusions often resolve spontaneously, while large effusions may merit evacuation. Other complications include: increased IOP, cataracts, strabismus and later erosion of the tube and seton plate.

Cyclocoagulation

Cyclocryocoagulation and cyclophotocoagulation are variations of cyclocoagulation in which the surgeon uses a special probe to freeze or photodynamically ablate part of the ciliary body. This, in turn, inhibits the production of aqueous fluid, resulting in decreased IOP.

Indications for cyclocoagulation include eyes that have poor visual potential or in which filtering surgery has a high failure rate (neovascular glaucoma, aphakic and pseudophakic glaucoma). The procedure is also indicated in patients who are unable to undergo filtering surgery and as a therapy for end-stage glaucoma.

In general, surgeons use it as a last-resort surgical treatment for glaucoma. The full effect of treatment may take two to four weeks to manifest. If the patient needs additional treatment, wait at least one month before referring for such. The surgeon may then retreat the same area or use another quadrant. However, one quadrant must remain untreated to avoid anterior segment necrosis.

Although cyclocoagulation is noninvasive, the results are less predictable and the risks greater than those of other glaucoma surgeries. Common complications include postoperative pain, hypotony, marked inflammation of internal and external eye structures, reduced visual acuity, and choroidal detachment and atrophy. Hypotony occurs in 8% to 12% of patients and may lead to the eye becoming too soft, resulting in visual impairment or loss. Also, 29% to 48% of patients may require one or more repeat treatments.

Investigational techniques

The following new surgical techniques are undergoing investigation for treating glaucoma:

Microendoscopic approaches to trabeculectomy. Microendoscopy allows the surgeon to perform trabecular surgery, such as goniocurettage (in which the surgeon removes pathologically altered trabecular meshwork to increase aqueous outflow) or photoablative laser goniopuncture, when corneal opacification might otherwise preclude adequate visualization and treatment.

Xe-Cl excimer laser. A beam of ultraviolet radiation creates openings in the trabecula and inner wall of Schlemm's canal to increase aqueous outflow. Early studies show that it produces significant reductions in IOP with no serious complications. While initial results are promising, long-term follow up is necessary.

Olivieri mask. This device consists of a small spatula with a triangular hole in the center. The surgeon manually creates the superficial flap, then positions the mask so that only a triangular portion of the sclera is exposed. This way, the excimer laser only ablates the triangular section of tissue, preserving the surrounding tissue.

Know what to tell them

As more of us manage glaucoma patients, our experience with all aspects of this disease increases. Our knowledge of the surgical options for treatment will aid us in educating our patients and in co-managing them -- at least until we're allowed to perform some of these procedures ourselves some day.

References available on request.

Dr. Gupta practices full-scope optometry at Stamford Ophthalmology. You can reach him at deegup4919@hotmail.com.