Glaucoma, Angle Closure, Chronic Treatment & Management

It is important to recognize early stages of appositional angle-closure in the absence of PAS and to recognize deep, circumferential angle-closure.

Laser iridotomy is indicated for all stages of chronic angle-closure glaucoma (CACG). Laser iridotomy involves the creation of a hole in the peripheral iris by laser.^{[25, 26]} The hole provides an alternative pathway for aqueous to flow from the posterior chamber into the anterior chamber, bypassing the pupil. Therefore, iridotomy will eliminate pupillary block and prevent forward bowing of the iris as a result of the pressure difference between the two chambers. Iridotomy will open those areas of the angle not involved by PAS and prevent further synechial closure.

Miotic treatment may enhance the development of CACG in the absence of an iridotomy. When miotic-induced angle-closure occurs, the approach to treatment should be determined by assessing the medications necessary to control the glaucoma. If a patient is taking dipivefrin, discontinuation may be enough to open the angle and allow the patient to remain on miotics, assuming that IOP remains under control. If the patient has been treated with miotics alone, substitution of aqueous suppressants may suffice. If the patient requires miotics for IOP control, then laser iridotomy is warranted.

If the angle remains appositionally closed or spontaneously occludable after laser iridotomy, argon laser peripheral iridoplasty (ALPI) is indicated to prevent progressive damage to the angle or further appositional and/or synechial closure of the angle.^{[27, 28, 29, 30]} If, after iridoplasty, some of the angle still remains appositionally closed, low-dose pilocarpine, such as pilocarpine 2% at bedtime, often suffices to maintain the patency of the angle.

The level of IOP and the extent of glaucomatous damage determine the need for continued medical treatment after iridotomy. Treatment is similar to that of open-angle glaucoma. Repeated gonioscopy is necessary. The need for further surgery cannot be predicted from the level of initial IOP or the gonioscopic changes. Argon laser trabeculoplasty (ALT) has been reported both to be successful and unsuccessful after iridotomy in combined mechanism glaucoma; however, overall it has been found to be reasonably successful.^{[31, 32]} If the pressure remains uncontrolled and glaucomatous damage develops, filtration surgery is indicated. An increased chance of developing malignant glaucoma is present following filtration surgery in patients who have had angle-closure glaucoma.

The two main challenges in the management of chronic angle-closure glaucoma are, firstly, to prevent progression of the angle closure, and, secondly, to prevent progression of the glaucomatous optic neuropathy by controlling intraocular pressure. Various surgical procedures have different roles to play to meet these challenges.

The diminishing role of surgical iridectomy

To prevent progression of the angle closure, all eyes with angle closure or very narrow drainage angles should have an iridectomy or iridotomy to eliminate pupillary block. Nowadays, laser iridotomy has largely succeeded surgical iridectomy, except in exceptional circumstances.^{[33, 34]}

Laser iridotomy has many advantages over surgical iridectomy. Laser iridotomy is noninvasive, so there is no inherent risk of endophthalmitis and wound complications, such as wound leak. With sequential laser techniques, the wound edge of the iridotomy is well coagulated and the risk of hemorrhage from iris tissue is much reduced. The movement of fluid when the iris is penetrated is a good sign of iris penetration, and the chance of an incomplete iridotomy is minimal. Furthermore, as no ocular incision is required, there is no risk of further shallowing of the anterior chamber and causing irido-corneal adhesion and damage, peripheral anterior synechiae and permanent closed angle, or precipitating malignant glaucoma. Laser iridotomy can also be conveniently performed in outpatient clinic, and it does not require operating room facilities.

As laser equipment and expertise have become widely available, the role of surgical iridectomy in the management of angle-closure glaucoma is now limited to those situations when laser iridotomy is not possible or effective, for example, in patients with significant corneal opacity. The inability of patients to cooperate may also be a relative indication for surgical iridectomy, which can be performed under sedation or even general anesthesia. Severe anterior chamber inflammation may repeatedly occlude a laser iridotomy, while the relatively larger iridectomy created by surgery is much more likely to remain open under such circumstances.

Trabeculectomy

Trabeculectomy is effective for CACG.^{[35, 36, 37, 38, 39]} Trabeculectomy has been shown to have an overall success rate of 68% in terms of intraocular pressure control. However, compared to primary open-angle glaucoma, any aqueous-draining procedure in an eye with a shallow anterior chamber and a chronic closed angle poses the risk of further shallowing the anterior chamber or precipitating malignant glaucoma. Trabeculectomy in CACG is associated with a higher risk of filtration failure, shallow anterior chamber, and malignant glaucoma/aqueous misdirection. As the incidence of CACG increases with age, many patients with CACG have co-existing cataract. Trabeculectomy increases the rate of cataract progression, and a significant proportion of patients will soon need cataract extraction after trabeculectomy.

Furthermore, future cataract extraction may result in loss of the functioning filter. It has been reported that 30-100% of previously functioning blebs required antiglaucoma medications to control intraocular pressure after extracapsular cataract extraction (ECCE). Trabeculectomy alone is, therefore, not the ideal surgical option in medically uncontrolled CACG.

In theory, adjunctive antimetabolite should be used with trabeculectomy when performed in eyes with a high risk of filtration failure or when a very low target pressure needs to be attained. However, the risk factors for filtration failure specific to angle-closure glaucoma, and the target pressure in angle-closure glaucoma, have not yet been clearly defined. Trabeculectomy is associated with various complications, both early and late, including bleb leaks and bleb-related infections. These risks are further increased by adjunctive antimetabolite.

Lens extraction

Lens position and thickness both play important roles in the etiology of angle-closure glaucoma.^[40] Lens extraction significantly increases anterior chamber depth and width of the drainage angle. Lens extraction has been actively studied and reported in recent years in the treatment of primary angle-closure glaucoma. The lens may narrow the angle by pushing the peripheral iris anteriorly, and this effect will be more marked if the lens is cataractous. Both traditional extracapsular cataract extraction (ECCE) and phacoemulsification have been reported to lower intraocular pressure in CACG. Phacoemulsification alone has also been shown to normalize intraocular pressure in chronic angle-closure glaucoma.

Hayashi has shown that the width and depth of the anterior chamber angle in eyes with angle-closure glaucoma increased significantly after cataract extraction and intraocular lens implantation, which may lead to the decrease in intraocular pressure seen in the postoperative period. Lens removal is associated with deepening of the anterior chamber and widening of the angle. It has been postulated that removal of a large cataractous lens from an eye with a crowded anterior segment may improve aqueous outflow. It has also been postulated that during phacoemulsification, the irrigating fluid flushes cellular debris from the trabecular meshwork, decreasing resistance to aqueous outflow.

One study suggested that the IOP-lowering effect of lens extraction may be less pronounced in CACG cases with PAS covering three fourths or more of the angle. Therefore, lens extraction alone may have a role in improving IOP control in CACG, especially in cases with less extensive PAS and when the IOP is not grossly out of control.

No randomized controlled trials have compared the efficacy and safety of lens extraction to other glaucoma surgeries in CACG. Two randomized controlled trials are currently being undertaken by the first author and his team in Hong Kong to investigate the effects of lens extraction in CACG cases with and without cataract. IOP control, surgical complications, and additional interventions for IOP control are important outcome measures in these studies. The study by Lai et al showed that, in patients with primary angle-closure glaucoma with co-existing cataract, cataract extraction alone (by phacoemulsification) can significantly reduce both intraocular pressure and the requirement for glaucoma drugs.

Combined lens extraction and trabeculectomy

Trabeculectomy for CACG is often combined with lens extraction with IOL implantation.^{[41, 42]} Since cataract extraction alone widens the angle and lowers IOP in CACG, trabeculectomy combined with lens extraction should have a greater intraocular pressure-lowering effect in CACG than in POAG. There is, however, no published data documenting the additional IOP-lowering effect of combined phacotrabeculectomy over trabeculectomy alone in CACG. Combined surgery also improves patients’ visual acuity and quality of life, with the added advantage of reducing the risk of anterior chamber shallowing or flattening.

The study by Lai et al showed that the success rates of phacotrabeculectomy in primary angle-closure glaucoma and primary open-angle glaucoma were not statistically different, although the intraocular pressure reduction was significantly greater in the primary angle closure.^{[43, 44, 38, 45]} Unfortunately, there are no data available on the exact amount of additional intraocular pressure lowering of glaucoma procedures combined with lens extraction. Trabeculectomy has been combined with phacoemulsification in the management of chronic angle-closure glaucoma and is reported to have an improved outcome because of the decreased surgical trauma from using a small incision.

As mentioned earlier, trabeculectomy alone has the disadvantage of shallowing the anterior chamber and allowing the iris-lens diaphragm to move anteriorly in the management of closed angle glaucoma. When trabeculectomy is combined with lens extraction, and replacement of the physiological lens with a much thinner artificial IOL, these problems are avoided. It is, therefore, recommended that the lens be removed at the time of trabeculectomy, even with early cataract. The authors recommend combined phacotrabeculectomy in CACG cases with some degree of cataract, especially when the IOP is not well controlled with maximally-tolerated medications.

Goniosynechialysis with/without lens extraction

Goniosynechialysis (GSL) is a surgical technique performed to strip the peripheral anterior synechiae (PAS) from the trabecular surface in the angle and provide aqueous renewed access to the trabecular meshwork.^{[46, 47, 48]} In eyes with minimal PAS, trabeculectomy is preferred because trabecular function in these eyes is expected to be poor and a fistula procedure would be more appropriate. On the other hand, there may be spikes of raised intraocular pressure during and after the GSL procedure leading to loss of vision. GSL is more suitable for eyes with a minimal to moderate degree of neuronal damage.

In the past, ophthalmologists have tried to sweep open a closed angle without direct visualization. This often failed because accurate instrument placement could not be achieved. In 1984, Campbell and Vela introduced a technique using direct intraoperative visualization of the angle and anterior chamber deepening with viscoelastic agents.^[49] Visualization has been further improved with the use of the Swan-Jacob lens. This specially-designed lens has a handle attached to a small diameter prism so that it will not obstruct the spatula from entering the anterior chamber at the limbus. When PAS has been present for less than 1 year, the overall success rate in terms of intraocular pressure control is approximately 80%. Irreversible damage to the meshwork may occur in areas of synechial closure, with proliferation of iris or fibrous tissue into the intertrabecular space. This may explain why GSL appeared to be less effective in closed angle of longer duration.

In order for GSL to be effective, it must be performed before there is irreversible histological change in the meshwork. The mechanisms causing the angle closure should also be eliminated by performing peripheral iridotomy, laser peripheral iridoplasty, or lens extraction, either alone or in combination, to minimize the possibility of recurrent closure. Tanihara and Nagata reported success in using GSL followed by argon laser peripheral iridoplasty.^[50]

The most common complication of GSL is intraoperative hemorrhage. Other complications include iridodialysis, cyclodialysis, and lens damage.

Teekhasaenee and Ritch have reported success with phacoemulsification combined with GSL, and Lai et al was successful with combined phacoemulsification and limited GSL, followed by diode laser peripheral iridoplasty, for chronic angle-closure glaucoma.^[51] The authors demonstrated with ultrasound biomicroscopy that lens removal in chronic angle-closure glaucoma would only deepen the peripheral anterior chamber, without actually opening up the angle, while GSL opened up the angle and allowed aqueous access to the trabeculum.

Nevertheless, both lens extraction and GSL performed alone have been shown to lower the intraocular pressure, although the mechanisms are uncertain and may or may not be common to both procedures. Combining GSL with lens extraction has the advantages of noticeable visual improvement after surgery, and the combined IOP-lowering effect of the two procedures. Furthermore, removal of the lens may decrease the possibility of recurrent angle closure.

Cyclodestructive procedures

In 1950, Bietti introduced cyclocryotherapy. A temperature of -80°C was applied with a cryoprobe to destroy the ciliary body epithelium, stroma, and vasculature. The clinical usefulness of cyclocryodestruction is limited by its complications, which include hypotony, phthisis, hyphema, choroidal detachment, and retinal detachment.

In the past 10 years, transscleral diode laser cyclophotocoagulation (TSCPC) using the G-probe is becoming more popular and is used to treat many different types of glaucoma.^{[52, 53]} The semiconductor diode laser emits light of wavelength 810 nm, near the infrared spectrum. It is transmitted through the sclera and absorbed by melanin. The success rates of cyclodestruction vary among the different procedures and the types of glaucoma. Diode TSCPC was reported effective in controlling intraocular pressure to less than 21 mm Hg in 70-81% of pediatric and adult refractory glaucoma. However, there has been no large-scale study on its efficacy in the treatment of CACG. Since it decreases intraocular pressure by destroying the ciliary epithelium and reducing aqueous production, it should, theoretically, be effective even in eyes with complete synechial closed angle closure.

In a recent study, adjunctive diode TSCPC was effective in lowering intraocular pressure in 4 cases of chronic angle-closure glaucoma that were uncontrolled despite a glaucoma aqueous tube shunt and multiple medications. In another study, diode TSCPC appeared to be an effective and safe primary surgical treatment of medically-uncontrolled chronic angle-closure glaucoma, with intraocular pressure-lowering effect persisting up to two years.

The efficacy and relative safety, the portability of the equipment, the ease of learning, and the short duration required for performing this technique make diode TSCPC a potential primary or secondary surgical procedure in the future treatment of chronic angle-closure glaucoma. However, TSCPC is associated with some rare but potentially serious complications, and these should be balanced against its many advantages. Potential complications include uveitis, pupillary distortion, conjunctival burns, hyphema, chronic hypotony, cystoid macular edema, retinal detachment, phthisis bulbi, and scleral perforations.

Glaucoma implants in chronic angle-closure glaucoma

The use of a glaucoma implant for difficult-to-treat glaucoma is not new. There is a wide variety of such glaucoma drainage devices, from the early Molteno implant to the currently popular valve-equipped variety, such as the Ahmed implant. Overall, the success rates for controlling intraocular pressure for complicated cases range from 70-90%. However, because it is technically more difficult than trabeculectomy, and potentially serious complications can occur, the use of a glaucoma implant for chronic angle-closure glaucoma has been mainly confined to those patients in whom one or more previous filtering procedures have failed.

Among the studies that included chronic angle-closure glaucoma, the proportion of patients with chronic angle-closure glaucoma ranged from 1.7-9%. Aside from the small number of patients, another major problem with these studies is that only two published the results of the subgroup with chronic angle-closure glaucoma. One had only a single non-Asian patient with angle-closure glaucoma, who ended up with no light perception at 6 months, while the other included 10 patients of unspecified race, 7 of whom had successful surgery.

A more recent randomized study evaluated non-valved tube shunt surgery against trabeculectomy in patients with glaucoma who had previously failed trabeculectomy and/or cataract extraction with intraocular lens implantation. In this study, there were 18 eyes with CACG, with 7 randomized to the implant group and 11 to the trabeculectomy group. In the former study, there were 15 eyes (23%) with the diagnosis of chronic angle-closure glaucoma, iridocorneal endotheliopathy, and juvenile open-angle glaucoma treated with the 350 mm² Baerveldt glaucoma implant. The immediate-term failure rate in this subgroup was 47%, compared with 19% in the group with primary open-angle glaucoma. Although this study did not provide a subgroup analysis for patients with CACG, the 1-year results found a higher success rate in the tube group compared to the trabeculectomy group. These results suggest a possible expanded role for the use of implants in eyes with previous ocular surgery.

Glaucoma specialist