Ординатура / Офтальмология / Английские материалы / Clinical Pathways in Glaucoma_Zimmerman, Kooner_2001

460 Surgical Therapy for Glaucoma

repeat trabeculectomy) as the backup protocol. ALT has also been used quite successfully as initial primary therapy in Egypt, where socioeconomic factors make other treatments more impractical.17 No doubt, socioeconomic factors and the availability of eye care greatly influence treatment patterns both in the United States and elsewhere.

Diagnosis and Differential Diagnosis

When Does Surgical Intervention Become Essential

in Glaucoma?

If medical therapy fails to prove adequate for protection of the optic nerve and visual fields, it is important to reevaluate the patient’s target IOP and overall condition. Is the patient compliant? Has the maximally tolerated medical therapy been completely explored? Could high blood pressure, atherosclerosis, nocturnal hypotension (from excessive nighttime systemic beta-blocker agents), anemia, a long-forgotten past hypovolemic/hypoxic episode, or even an undiagnosed intracranial tumor have been contributing factors?

How Is the Decision Made to Intervene Surgically in Glaucoma?

If high IOP is thought to be a major problem, it is always a good idea to repeat gonioscopy prior to considering laser or surgical intervention. It is not uncommon for what was once thought to be primary open-angle glaucoma (POAG) to slowly progress to an accompanying component of chronic narrow-angle glaucoma (especially in blacks) or phacomorphic glaucoma (especially in elderly hyperopes with nuclear sclerotic lens changes). Occasionally, neovascular glaucoma (NVG) is initially overlooked in its earlier stages in patients with diabetes, carotid artery occlusion, or retinal vein occlusion.

Treatment and Management

How Does One Decide Which Procedure to Do First?

Figure 19–1 outlines the management of patients when maximal medical therapy fails to adequately control IOP. If gonioscopy reveals an open angle, ALT is the first procedure of choice. If this fails, surgical guarded trabeculectomy is indicated. Antimetabolites are used in conjunction with primary trabeculectomy in many patients who are at high risk for failure (younger patients, blacks, patients with a history of prior eye surgery, etc.). Antimetabolites are strongly indicated in patients who have had a prior failed trabeculectomy. If two or more guarded trabeculectomies have failed, or if a patient has neovascular glaucoma, a seton device is usually indicated. Antimetabolites probably should not be used with seton devices.18

Figure 19–1. Management of patients with medically uncontrolled glaucoma.

If gonioscopy reveals the angle to be closed, then compression gonioscopy can be helpful. If the angle compresses open, a laser peripheral iridotomy (LPI) will likely be helpful. If after iridotomy the angle opens but the IOP remains elevated, consider ALT or guarded trabeculectomy (probably with an antimetabolite). If the angle is not open following LPI, then the patient may have plateau iris (rare) or phacomorphic narrowing (more common). Phacomorphic narrowing will have a convex or volcano iris plane in contrast to the flatter iris plane of plateau iris. Gonioplasty is often helpful in patients with phacomorphic narrowing and may be useful in facilitating visualization prior to ALT in

likely that a second treatment will help. If the first treatment involving 180 degrees of the angle was successful, but over time the IOP has again risen, then it is reasonable to attempt another treatment in the remaining 180 degrees of TM. Do not treat if you do not have a clear shot at the TM; hitting the peripheral iris in the angle will lead to extensive formation of PAS. Avoid treating an area of scarred angle or an area of PAS. Try to treat only the functioning angle as identified by an area with some pigmentation in the TM. Atrophic parts of the TM are distinctively nonpigmented. They take up laser poorly and, even if treated, provide minimal if any effect. It is not worth treating these areas.

Is There a Need for Medical Prophylaxis Before ALT?

If not otherwise contraindicated, preand postlaser treatment with Iopidine 1% (apraclonidine 1%) can significantly reduce chances of pressure spikes following both ALT and LPI.23 Alternatively, some surgeons are using Alphagan (brimonidine tartrate 0.2%) as a substitute, although one must be aware that the pressure-lowering effect may not be as great. Cooling the eye (ice packs) is also effective, but most find this less practical.

What Is the Procedure for ALT?

The procedure for ALT is as follows:

•Preoperative apraclonidine 1% is given at least one half-hour before the procedure.

•Focus both oculars so aiming beam is parfocal.

•Topical anesthesia is delivered and the Goldmann lens is used to view the angle.

•The dye laser is “tuned” to the all-green mode or the argon laser is set on the green mode.

•Spot size is 50 m.

•Time is 0.1 seconds.

•Power settings vary with different lasers and degrees of angle pigmentation. A common initial power setting in a medium pigmented eye with a dye laser in the green mode is between 200 and 400 milliwatts (mW). The power is adjusted to just produce a white blanch at the juncture of the anterior TM (nonpigmented) and posterior TM (pigmented). If a bubble is produced for a microsecond, then the laser power is turned down. Conversely, if no blanch is seen, then the power is turned up. This assumes the surgeon is in a functioning (not atrophic) angle. It also assumes that the argon aiming beam is well focused and centrally located within the gonioscopic mirror of the Goldmann lens, and that the target is the juncture of the nonpigmented and pigmented trabecular meshwork. If the desired effect is not seen, the laser is turned up or down by 50-mW increments until the desired target intensity is reached.

•Darker pigmented TM will absorb more laser and therefore requires less energy.

•Lighter pigmented TM will absorb less laser and therefore requires more energy.

•The atrophic angle will not have pigment and will not take up laser.

464 Surgical Therapy for Glaucoma

•Aim for the junction of the anterior TM (nonpigmented) and the posterior trabecular meshwork (pigmented). This normal anatomy is seen in areas of functioning angle. If it is not well demarcated, then it is likely not worth treating that area!

•The number of shots varies according to how much functioning angle is viewable. Most surgeons leave a space equal to the width of the aiming beam between each laser application. Assuming the total angle is viewable and normal in appearance, the average number of applications per 180 degrees of treated angle is approximately 45 shots.

•Apraclonidine 1% is given immediately postop; prednisolone acetate 1% (Pred Forte) or loteprednol elabonate (Lotemax) are given q.i.d. for 4 days, or as needed.

•IOP is checked at 1 hour and at 1 to 7 days postoperatively.

How Effective is ALT?

Eighty percent of eyes initially respond with a significant reduction in IOP. After 5 years, 50% of eyes are thought to still have a measurable pressure lowering effect.24

What Are the Complications of ALT?

The most common side effect of ALT is a transient increase in IOP (pressure spike) and/or inflammation (cells and flare). Preoperative and postoperative apraclonidine 1% and postop antiinflammatory agents have greatly reduced the chance of these side effects.

What Are the Indications for LPI?

LPI is the primary treatment of choice for acute narrow-angle glaucoma and chronic narrow-angle glaucoma due to pupillary block. It has a more subjective use in the prophylaxis for prevention of narrow-angle glaucoma in patients at high risk. Likewise, there is some indication for prophylaxis in patients with relative pupillary block (intermittent narrowing of the angles). More recently, LPI has been found useful in select patients with pigment dispersion syndrome.25 It does not resolve plateau iris configuration, but this diagnosis is usually not made until LPI has already been attempted because it is a diagnosis of exclusion.

What Is the Mechanism of Action of LPI?

LPI relieves the buildup of pressure in the posterior segment due to relative or absolute pupillary block. By providing an alternate route for aqueous humor to pass from the posterior segment to the anterior segment, there is no longer pressure buildup behind the iris from an occluded pupil. In the pigment dispersion syndrome, a transient increase in the pressure of the anterior chamber compared to the posterior chamber can push the midperipheral iris back onto the zonules and cause dispersion of pigment in some patients. An iridotomy theoretically equalizes the pressure gradient in these cases.

How Is LPI Performed?

LPI can be accomplished with the yttrium-aluminum-garnet (YAG) or argon laser. The YAG laser penetrates the iris quicker and is the most common type used. The argon laser is still sometimes used to pretreat (before the YAG laser), to cut down on the incidence of iris bleeding. This may be especially helpful in patients on coumadin or aspirin therapy. Argon lasers are quite poor for penetrating lightly pigmented irides and YAG lasers will often be necessary in these eyes.

What Are Some Principles to Consider in Site Selection of LPI?

•Avoid any surface iris vessels.

•Look for deep crypts to reduce the amount of tissue through which the laser has to penetrate.

•Apply the laser at 11 o’clock or 1 o’clock on the peripheral iris. The purpose of having the iridotomy superiorly is so that the upper lid will cover the iridotomy and prevent monocular diplopia or glare. The purpose of treating at 11 o’clock or 1 o’clock as opposed to 12 o’clock is that lasers sometimes form bubbles. Bubbles can obscure the view of the area being treated. Bubbles will usually float up to the 12 o’clock peripheral iris.

•Site selection is of major importance. The goal is to be peripheral enough to avoid hitting the lens. (In fact, an LPI that has underlying lens apposition is useless.) At the same time, if you are too peripheral, the view will be clouded by the peripheral haze of the cornea. The cornea runs more obliquely and is thicker (and therefore more opaque) at the far periphery, and so visualization at the far periphery is poor. Also, because of the shallowness of the chamber in this location, corneal endothelial damage is more common at the far periphery.

What Are Some of the Specifics in Performing LPI?

•Apply apraclonidine 1.0% preoperatively.

•Apply pilocarpine 1.0% preoperatively to flatten iris.

•Apply Abraham eccentric lens.

•Set YAG power to 4–5 millijoules (mJ) on double burst mode and apply laser.

•Refocus deeper and reapply laser until penetration achieved.

•Give apraclonidine 1.0% again postoperatively.

•Check IOP at one hour and then as needed.

•Start topical steroids postoperatively for 4–7 days.

What Are Some Other Considerations When Performing LPI?

If the laser penetrates full thickness, then a pigmented fluid wave will be visualized coming forward through the iridotomy site. If this is not seen, refocus at a new depth of the same site and reapply laser. Remember that as one goes posterior into the iris and approaches the posterior segment, the power setting should be reduced to avoid posterior segment damage.

466 Surgical Therapy for Glaucoma

With a power setting of 4 to 5 mJ depending on iris thickness, and in the double burst mode, a patent YAG LPI is usually accomplished in one to three applications. Occasionally, more applications are needed. It is best to wait for the pigment to clear after one shot before shooting again. If moderate pigment is dispersed after three or four shots in an elective procedure, it is sometimes best to postpone further laser treatment for another time to prevent pressure spikes. If it is clearly evident that progress is not being made, it is usually best to try a different site. Complementary argon laser treatment in dark, thick irides is sometimes helpful. Likewise, supplemental argon laser treatment is very helpful to stop unexpected iris hemorrhaging that sometimes occurs during a YAG laser procedure. For these reasons it is ideal to have both lasers located in the same room for these reasons. Very rarely, one may have to resort to surgical iridectomy in patients with thick irides.

What Are the Complications Associated with LPI?

Hemorrhaging and pressure spikes are the most common complications. If a hemorrhage occurs during laser treatment, then gentle pressure to the globe with the Abraham lens will often stop the bleeding. Continue holding pressure for a minute and then recheck to see if it is still bleeding. This can be repeated several times. If this fails to stop the bleeding, it is best to proceed with argon laser cautery to the area.

Pressure spikes are usually controlled medically (may require mannitol). Patients should be warned, however, that rarely a dangerous pressure spike may occur and necessitate trabeculectomy.

How Effective Is LPI?

Almost always, a single, patent iridotomy is successful in preventing or relieving pupillary block. The degree of success for treating select patients with pigment dispersion syndrome is not yet known.

What Are the Indications for Argon Laser Gonioplasty?

A gonioplasty may be indicated when angle crowding of the iris persists in a patient with narrow-angle glaucoma who has already had a peripheral iridotomy. Usually, this occurs in patients who have a superimposed degree of phacomorphic or plateau iris crowding. Also, it is often used to facilitate visualization of the angle prior to ALT in these patients. Argon laser gonioplasty is used usually as a temporary measure in patients who are not yet otherwise ready for cataract surgery or combined cataract/glaucoma surgery.

What Is the Mechanism of Action of Gonioplasty?

The procedure uses the argon laser to burn areas of iris stromal tissue in the peripheral iris. This results in contracture of tissues and pulls the peripheral iris from the angle. In cases with some degree of phacomorphic component, it may flatten and stiffen the midperipheral iris to reduce its anterior bulge.

468 Surgical Therapy for Glaucoma

ments may be more cost conscious. In some cases, multiple medical therapy may simply be too expensive as a lifetime treatment. It is also known that medication and preservatives in topical eye drops taken long-term can increase bleb scarring and thereby reduce surgical success.26,27 Even ALT has been linked as a possible cause of encapsulated blebs following filter surgery.28 Another study found male gender to be a risk factor for bleb encapsulation, but the risk from ALT was not statistically significant in that study.29 All of these factors have generated a push by some toward primary trabeculectomy.1

In this country, patients are living longer and our attitudes are changing as to how low pressure must remain in order to reasonably sustain optic nerve function for a given patient’s lifetime. We are being more aggressive with IOP and are proceeding with surgery at earlier stages than in the past. It is important to remember, however, that the incidence and severity of complications with glaucoma surgery is still relatively high compared to other ophthalmic procedures (e.g., cataract surgery, refractive surgery, etc.). Also, success is much less predictable in glaucoma surgery compared to other eye procedures because outcome is so dependent on each patient’s individual scarring response (determines bleb success) and preexisting degree of outflow obstruction (determines how much filtration a given surgery must achieve in order to lower IOP). Furthermore, many of our latest and most potent topical medications (Xalatan, Alphagan, Cosopt, to name a few) were not available when the trend toward primary trabeculectomy began with the ”Moorfield studies” of the 1980s.5–8

Even with the most successful glaucoma surgery, it is common to have some increase in the cloudiness of the lens.30 In addition, many patients will be forever symptomatic because of their well-functioning bleb (foreign body sensation). Furthermore, all patients with a functioning bleb are at a lifetime risk for bleb infection and possible endophthalmitis. For all of these reasons, surgical trabeculectomy is generally reserved for patients who remain at high risk despite prior medical and laser therapy.

What Is Guarded Trabeculectomy?

There are an infinite number of variations of glaucoma filtration surgery (Table 19–3). The guarded trabeculectomy is the procedure of choice for most patients. These procedures can utilize either a fornix-based conjunctival incision (conjunctiva is opened at the limbus) or a limbal based conjunctival incision (conjunctiva is opened about 10 mm posterior to the limbus and dissected forward). Each type of conjunctival incision has advantages and disadvantages with corresponding proponents and opponents.

The majority of trabeculectomies are performed under local anesthesia using peribulbar or retrobulbar anesthesia. A peribulbar block is considered safer than a retrobulbar block and therefore is usually recommended. Usually a 1:1 mixture of lidocaine 2% with Marcaine 0.75% is used along with Wydase. More recently, topical anesthesia combined with localized subconjunctival lidocaine 2% and intracameral nonpreserved lidocaine 1% has been occasionally used. This method does not work in all cases because of the lack of adequate akinesia. General anesthesia is sometimes advocated in monocular patients at high risk for retrobulbar or peribulbar anesthesia.