If glaucoma medical therapy fails, a broad range of surgical approaches is available

Although the vast majority of our glaucoma patients are well managed with medical therapy, there remain patients who need surgery to preserve their vision. Surgical techniques for reducing IOP in glaucoma patients include laser trabeculoplasty, trabeculectomy, nonpenetrating filtration surgery, shunts and cyclodestruction procedures.

Laser trabeculoplasty

Argon laser trabeculoplasty (ALT) is one of the most commonly performed glaucoma surgeries. The procedure entails the use of an argon laser (blue-green to green wavelength) to create small laser burns around the trabecular meshwork to increase aqueous fluid outflow. The thermal effect of the burns induces collagen shrinkage and scarring of the trabecular meshwork. This leads to mechanical traction on the adjacent inter-trabecular spaces. As these spaces are opened, outflow facility is increased, and IOP is decreased.

The procedure typically begins with the patient seated at the slit lamp with a goniolens. Typically, half (180°) of the angle is done, and the other half is reserved for future treatment. The laser spots are positioned at the junction of the pigmented and nonpigmented trabecular meshwork, with a gap of the diameter of two laser spots between spots. If the laser burn is placed too anterior, the treatment tends to be ineffective. If it is placed too posterior, there is a greater likelihood of inducing inflammation and peripheral anterior synechiae.

Laser trabeculoplasty was traditionally used when maximal medical therapy failed to adequately control IOP. Recently, however, the Glaucoma Laser Trial established the efficacy of ALT as a primary treatment in lowering IOP in open-angle glaucoma. The studies reported that patients treated with ALT as a primary treatment had better IOP control and better visual field and optic disc status than those treated initially with topical medications.

However, I believe most optometrists would feel this treatment is too aggressive. With the quality of medications on the market, there is no reason not to try medical therapy first before sending a patient for surgery. In general, I recommend waiting on surgery until one of three things happen:

• there is a pattern of poor IOP control due to poor efficacy of medications;
• there is progressive damage (as shown by visual field, GDx [Laser Diagnostic Technologies, San Diego] or HRT II [Heidelberg Engineering, Vista, Calif.]) despite adequate IOP control;
• there is a lack of compliance that shows no signs of improvement.

In most patients, IOP following ALT rises less than 5 mm Hg, reaches its peak at 3 hours and resolves within 24 hours. However, a few patients will demonstrate larger, less transient IOP spikes that cause optic nerve damage and visual field loss. For this reason, you should see the patient several hours after the procedure and after 1 week to check for IOP spikes and at 6 to 8 weeks to check for efficacy of the procedure.

The risk of IOP spikes can be greatly reduced with the instillation of a drop of Iopidine (apraclonidine, Alcon) or Alphagan (brimonidine tartrate 0.15%, Allergan) 1 hour before and immediately after the procedure. Other complications of laser trabeculoplasty are relatively uncommon and are usually short lasting. They include decreased vision, pain, corneal burns, hemorrhage, peripheral anterior synechiae, iritis and adverse effects on filtration surgery.

In most cases, it takes 4 to 6 weeks for the full effect of the procedure to be evident. Factors affecting efficacy are age, race and type of glaucoma. Patients older than 40 years typically respond better than younger patients. Race does not appear to affect the short-term efficacy of laser trabeculoplasty, but African-American patients do have a lower long-term success rate.

Studies show that the efficacy of laser trabeculoplasty in controlling glaucoma decreases with duration of follow-up. In general, ALT controls IOP in 80% of eyes at 1 year, 50% at 5 years and 30% at 10 years. This means that laser trabeculoplasty provides adequate IOP control after 5 years for approximately half of the patients. Unfortunately, this also means that half of your patients will need additional therapy after 5 years, and 70% will need additional treatment after 10 years. Some newer studies have found success rates as low as 10% after 5 years depending on the patient profile. This is a problem, because coagulative damage to the trabecular meshwork from ALT may limit the efficacy of further therapy.

Selective laser trabeculoplasty

Selective laser trabeculoplasty (SLT) is a new laser technique that selectively targets melanin within trabecular meshwork cells using a Q-switched frequency-doubled Nd:YAG laser. This is an improvement from ALT in which all cells, both pigmented and nonpigmented, are targeted. Another major improvement in SLT is that it causes no thermal damage or subsequent scar formation to the trabecular meshwork as ALT does.

If studies prove that this procedure is as effective long-term, this may replace ALT as an initial surgical treatment for primary open-angle glaucoma (POAG).

This procedure has the same postop care and concerns as ALT.

In a randomized study comparing ALT and SLT as a second procedure after a failed initial ALT, IOP reduction was better after SLT than repeat ALT. These studies demonstrate that 70% of the patients had an IOP reduction of at least 3 mm Hg and an average IOP reduction of 5 mm Hg to 6 mm Hg. Because it is still a relatively new procedure, more research is necessary to evaluate the efficacy of SLT.

Trabeculectomy

The most common non-laser surgical procedure for managing glaucoma is a trabeculectomy, or filtering surgery as it is commonly called.

In this procedure, the surgeon removes a piece of the cornea or sclera, creating an alternative pathway for aqueous fluid to leave the anterior chamber. The aqueous fluid pools in a reservoir, or bleb, under the eyelid where it is gradually absorbed by the episcleral venous drainage. The net effect is that IOP is reduced by surgically increasing outflow facility.

Post-trabeculectomy: This procedure is most effective for cases of uncontrolled primary open- and closed-angle glaucoma, exfoliation syndrome and pigmentary glaucoma.

The procedure varies with the type of suture used, type of conjunctival flap, closure technique and the use of antifibrotic agents. The purpose of these agents is to help prevent trabeculectomy failure due to scar formation.

Two of the more common antifibrotic agents used are mitomycin C, which is used intraoperatively, and fluorouracil, which is administered as subconjunctival injections postoperatively. The problem with using antimetabolites in filtration surgery is that they can lead to complications of their own, such as thin, avascular blebs, hypotony, endophthalmitis, wound leakage, toxicity to the corneal epithelium, delayed conjunctival healing and late-onset infection possibly leading to endophthalmitis.

This surgical intervention is generally used after medical and laser therapies fail to reach target IOP. Trabeculectomy is most effective for cases of uncontrolled primary open- and closed-angle glaucoma, exfoliation syndrome and pigmentary glaucoma. The secondary glaucomas (such as neovascular, uveitic, developmental, traumatic, aphakic, congenital, etc.) generally have a much poorer prognosis with filtration surgery and may require other treatment modalities. It is most commonly used after both medical therapy and laser surgery fail to properly control IOP. In severe cases of glaucoma where there is little healthy rim tissue, or in cases where the IOP is extremely elevated, some doctors may elect to go directly to a trabeculectomy in lieu of ALT or SLT.

Postop care of the patient undergoing trabeculectomy in the first 2 weeks is concentrated on monitoring for leaks and vascular integrity of the bleb, checking the anterior chamber for proper depth and for cells and flare, and examining the posterior pole for choroidal effusion. Subsequent postop visits can focus on evaluating the efficacy of the procedure. The most common problem following trabeculectomy is postoperative shallowing of the anterior chamber, usually caused by wound leak or excessive filtration. Bleb leaks can sometimes be managed conservatively; in other instances, surgical repair is necessary. Fortunately, sustained severe shallowing is rare, and many chambers re-form spontaneously. Early failure of the bleb is also possible. Management techniques may include scleral depression, digital massage, suture lysis and treatment with fluorouracil or corticosteroids.

The 5-year Collaborative Initial Glaucoma Treatment Study (CIGTS) found that both medication and filtering surgery are effective for short-term primary treatment in open-angle glaucoma. Trabeculectomy, alone or in combination with medical therapy, has a success rate approaching 95% at 2 years. Long-term, the results are not as optimal. After 5 years, many patients who have had trabeculectomy surgery may require additional therapy or a repeat procedure. Some studies have these numbers as high as 60% to 80% depending on patient characteristics.

Nonpenetrating filtering surgery

Nonpenetrating filtering surgery is a relatively new glaucoma procedure that is similar to trabeculectomy except that a thin membrane is created under the scleral flap without penetrating the eye. Nonpenetrating surgeries are divided into two groups: bleb-forming surgeries and viscocanalostomy. Bleb-forming surgeries include ab externo trabeculectomy (AET) and deep sclerectomy.

In AET, the surgeon creates a thin membrane by excising the inner wall of Schlemm’s canal and the juxtacanalicular trabeculum. In deep sclerectomy, the surgeon removes corneal stroma behind the anterior trabeculum and Descemet’s membrane. In a viscocanalostomy, the surgeon removes a deep piece of scleral tissue along with part of the trabecular meshwork and anterior Schlemm’s canal wall. When this is done, aqueous fluid bypasses the trabecular meshwork and percolates through an intact Descemet’s window.

The indications for this procedure are the same as for trabeculectomy.

The complications, while at a lower incidence, are the same as with a trabeculectomy. Also, there is a decreased need for anti-metabolites.

Nonpenetrating deep sclerectomy is generally less effective than trabeculectomy in lowering the IOP. More studies are needed to evaluate its true potential in glaucoma management.

Tube shunts

In this procedure, a tiny plastic tube is routed from the anterior chamber of the eye to a plate inserted halfway back around the eye. IOP is decreased as aqueous fluid drains through the tube to the top of the plate, where it is absorbed by ocular blood vessels. Some shunts have valves, some do not. The nonvalved shunts include Molteno implants, the Baerveldt and the Schocket encircling tube. Valved implants include the Krupin disc, Ahmed valve and White pump.

Patients who have significant scarring from previous glaucoma surgeries or glaucoma that is resistant to other forms of treatment may do well with an aqueous shunt. Tube shunts are useful in a variety of situations, such as inflammatory glaucoma (Posner-Schlossman), angle-closure glaucoma and certain cases of chronic open-angle glaucoma. Shunts may also be indicated in patients with angle-closure glaucoma due to inflammatory peripheral anterior synechiae or neovascularization. Patients with progressive angle closure, such as iridocorneal endothelial (ICE) syndrome and epithelial downgrowth, also do well with shunts.

Postop care of these patients is crucial. It many cases, the glaucoma specialist performing the surgery handles much of it until the patient can safely be turned back over to the referring optometrist. The most common early postoperative complication is hypotony, with or without associated choroidal effusions. Small choroidal effusions will often resolve spontaneously, while large effusions that result in “kissing choroidals” may have to be evacuated.

Increased IOP may occur as an early postoperative complication, usually because the silicone tube is blocked. Shunt patients with crystalline lenses develop cataracts more rapidly than normal or experience an acceleration of any pre-existing cataracts. Many of them require cataract extraction within 2 years of shunt surgery. In 3% to 6% of patients, shunts lead to the development of strabismus due to rectus muscle fibrosis or elevation of the cyst, causing globe displacement.

Shunt procedures in general do not result in very low IOPs, regardless of the kind of shunt used. In many studies, success is defined as an end IOP less than 21 mm Hg, which may or may not be enough clinically to stop the progression of the disease. Unfortunately, in many cases, pressures lower than this may not be possible to achieve because shunt procedures are typically used for the most recalcitrant cases of glaucoma. Based on this 21 mm Hg target IOP, success rates tend to be about 75% to 80%.

Cyclocoagulation

Cyclocryocoagulation and cyclophotocoagulation are variations of a procedure that works by using a special probe to freeze or photodynamically ablate part of the ciliary body. Thus, the production of aqueous fluid is inhibited, resulting in a decrease in IOP.

Indications for this procedure include eyes that have poor visual potential (visual acuity less than 20/400), eyes in which filtering surgery has a high failure rate (neovascular glaucoma, aphakic and pseudophakic glaucoma), patients who are unable to undergo filtration surgery and as a therapy for end-stage glaucoma. In general, it is used as a last resort treatment surgery for glaucoma if all other options have failed.

Although this procedure is noninvasive, the results are less predictable, and the risks are greater than some of the other glaucoma surgeries. Common complications include postoperative pain, hypotony, marked inflammation of internal and external eye structures, reductions in visual acuity, choroidal detachment and atrophy. In addition, 29% to 48% require one or more repeat treatments of cyclophotocoagulation.

The full effect of treatment may take 2 to 4 weeks to become evident. If additional treatment is needed, you should wait until at least 1 month has elapsed. At that time, the same area may be retreated, or another quadrant may be used. Care must be taken to ensure that one quadrant is left untreated to avoid anterior segment necrosis.

In many cases, medical treatment will sufficiently preserve your patient’s vision for the duration of his or her lifetime. When it doesn’t, you must be aware of the various surgical interventions, because your goal as the doctor is to preserve your patient’s vision over the course of his or her lifetime — by whatever means necessary.

For Your Information:

• Deepak Gupta, OD, is a columnist for Primary Care Optometry News. He can be reached at 1275 Summer St., #A-1, Stamford, CT 06905; (203) 327-5805; fax: (203) 352-5199; e-mail: deegup4919@hotmail.com.