Goniosynechialysis

Introduction

Primary angle closure (PAC) is an anatomical disorder of the eye characterized by iris apposition to the angle wall. Although laser iridotomy is considered to be the definitive treatment, up to 58% of patients with PAC continue to have elevated intraocular pressure (IOP) requiring postoperative glaucoma medication. The incidence of residual angle closure is increased in patients who have had prolonged angle closure prior to the iridotomy. Postoperative IOP control depends on the amount of trabecular meshwork damage and extent of peripheral anterior synechiae (PAS). Progressive irreversible endothelial damage and subsequent occlusion of the Schlemm's canal and trabecular meshwork will eventually occur if the PAS remain untreated.

There is a direct but nonlinear relationship between IOP and degrees of synechial closure. The IOP is usually elevated when >180° of the angle is closed by the PAS. When >270° of the angle is closed, medical therapy is usually ineffective and filtering surgery becomes necessary. Nevertheless, filtering surgery has several potentially serious complications which are more prevalent in eyes with PAC. Flat anterior chamber and malignant glaucoma tend to occur more frequently. The routine use of anti-metabolites increases postoperative endophthalmitis and bleb leak. In addition, filtration is subjected to closure by the healing process and the success rate decreases over time. A more logical approach is to eliminate the PAS and restore the trabecular function prior to the ultrastructural changes. Filtration through the natural trabecular pathway should be more physiologic and reliable than the artificial channel of filtering surgery .

Argon laser peripheral iridoplasty can open an appositionally closed angle, but does not eliminate PAS. Goniosynechialysis (GSL) is a surgical procedure designed to strip the synechiae from the angle wall and restore the trabecular outflow. Shaffer first described the procedure by using a cyclodialysis spatula and intraoperative gonioscopy. However, anterior chamber collapse and uncontrollable hemorrhage made the procedure unpopular. Chandler and Simmons proposed anterior chamber deepening as a diagnostic and therapeutic procedure for the unresolved acute PAC. Nevertheless, the procedure does not eliminate extensive or long-standing PAS. Most PAS are firmly established and resistant to such gentle efforts. Campbell and Vela described a modified technique employing a viscoelastic to maintain the anterior chamber and control hemorrhaging, while using an irrigating spatula to separate the PAS ( Fig. 108-1 ). The procedure was successful in 80% of eyes with minimal complications if the PAS had been present for less than one year. Later studies have confirmed the effectiveness of GSL in reducing PAS and improving IOP control. A study has shown an increase in the tonographic outflow facility following removal of the synechiae. The procedure is effective in separating the synechiae not only in PAC but also in secondary angle closure following vitreoretinal or filtering surgery.

The success of GSL depends not only on the preoperative duration but also the recurrence of the PAS. Although pupillary block has been eliminated by iridectomy, progressive angle closure can continue if non-pupillary block mechanisms are also present. It has been shown that nearly 60% of patients with a successful surgical iridectomy or 38% with a patent laser iridotomy still have a positive dark room prone provocative test. Recurrent attacks and further angle closure have been reported in both the attacked and the fellow eyes. Factors contributing to the reformation of PAS are early postoperative inflammation, plateau iris configuration, and the presence of an enlarged or anteriorly situated lens. It has been shown that cataract formation progresses rapidly following an acute attack. A thickening cataractous lens would crowd the anterior chamber and force the iris back against the trabecular meshwork.

Substantial increases in anterior chamber depth and angle width following cataract extraction with intraocular lens (IOL) implantation have been demonstrated in eyes with PAC ( Fig. 108-2A,B ). The narrower the preoperative anterior chamber angle, the greater the alteration of angle configuration. Whereas iridolenticular contact was observed in a phakic eye, there was no iris and IOL contact in a pseudophakic one ( Fig. 108-2A,B ). The iris plane shifted backward, deepening the central anterior chamber by approximately 850 µm. Preoperative biometry performed in a series of 52 eyes of 48 consecutive Thai middle-aged patients who had developed acute PAC within 6 months showed that average natural lens thickness and central anterior chamber depth were 4.83 mm and 1.8 mm, respectively. Since the IOL (PMMA, silicone, acrylic) thickness in the 20–25 D power ranges from 0.75 mm to 1.42 mm. Replacement of the natural lens with the IOL provided up to 4 mm more axial distance within the anterior segment eliminating angle crowding and appositional closure. In addition, anterior chamber deepening with a viscoelastic during IOL implantation might break recent PAS.

Several studies have shown that extracapsular cataract extraction (ECCE) with IOL implantation is effective in opening the angle and controlling IOP in refractory PAC. Currently, ECCE has been replaced by phacoemulsification which offers a higher surgical success rate, less postoperative inflammation and fewer complications. In addition, the clear corneal approach spares the superior conjunctiva for possible filtering surgery, if needed. Phaco­emulsification and IOL implantation has been reported to be highly effective in patients with uncontrolled PAC. However, up to 32% of the patients still had persistent PAS and required long-term treatment with glaucoma medication following lens removal either by ECCE or phacoemulsification and IOL implantation alone ( Fig. 108-2A ). Goniosynechialysis is the next step to eliminate the remaining synechiae and control the IOP ( Fig. 108-2C ).

Goniosynechialysis becomes more effective when performed after lens removal. An increase in the anterior chamber space provides ample room to perform the procedure and reduces the chance of synechial reformation. Combined phacoemulsification and GSL (phaco-GSL) has been shown to be safe and highly effective in controlling IOP (<21 mmHg) and decreasing PAS in >90% of 52 eyes that developed acute PAC within 6 months and had persistent IOP elevation following laser treatment. Postoperative IOP was reduced to below mid-teens regardless of the preoperative IOP level. Recurrence of the PAS, although uncommon, might occur during the first three months. The success of phaco-GSL has been stable since the third postoperative month for up to 14 years, providing a long-lasting control or even a permanent cure. A recent multicenter study also demonstrates a success rate (< 21 mmHg) of 85.9% in 109 eyes with uncontrolled PAC/PACG at one and three years following phaco-GSL.

Indications

Goniosynechialysis is best for patients who have had previously normal trabecular meshwork that has recently developed PAS on the basis of acute or chronic PAC, surgical procedures such as cataract extraction and penetrating keratoplasty, or trauma. Patients with acute PAC should have uncontrolled IOP and persistent PAS following successful laser iridotomy and laser peripheral iridoplasty. The extent of PAS should be >180° and correlates with the IOP. If not, an open-angle mechanism may coexist and makes the prognosis unfavorable. The shorter the duration of synechial closure, the better the prognosis. However, a postoperative fibrinous anterior chamber reaction commonly occurs if the operation is performed during the first four weeks after the acute attack. The optimal timing for phaco-GSL is suggested at week six after the attack when the eye becomes quiet.

Contraindications

Goniosynechialysis is contraindicated in patients who are likely to have ultrastructural changes of the trabecular meshwork from long-standing PAS. The presence of severe glaucomatous optic nerve cupping or extensive visual field loss should suggest long-standing asymptomatic closure despite a history of a recent acute attack. Patients with congenital angle anomalies and secondary angle closure following uveitis or anterior membranous pulling from neovascularization, iridocorneal endothelial syndrome, or posterior polymorphous dystrophy, are poor candidates.