68

Treatment of Occludable Angles and Angle Closure With Cataract Extraction

Michael A. Alunni, MD and Garry P. Condon, MD

Glaucoma has been ranked by the World Health Organization as the leading cause of irreversible blindness, and the expected prevalence of this condition is on the rise.¹ Between the 2 subtypes of glaucoma, open angle and angle closure, primary angle-closure glaucoma (PACG) is more severe and likely to result in permanent vision loss if not properly treated. PACG currently affects 20 million people, and it is projected that 34 million will be affected by 2040, with 5.3 million of these individuals being blind.²

In the early stages of primary angle closure (PAC), there is significant elevation in intraocular pressure (IOP) but not immediate visual loss. As we know, the standard of care is laser peripheral iridotomy (LPI) to open the anterior chamber angle and medical management to lower IOP. However, if these measures are not successful, then surgical management, usually with trabeculectomy, is indicated. More aggressive glaucoma surgeries such as this have higher potential for serious complications, which can impact visual outcomes.

An alternative approach in the management of PACG is surgical lens extraction. Age-related growth of the crystalline lens plays a major role in the mechanisms leading to PACG, and surgical removal of this lens, whether a visually significant cataract or a clear lens, can be a successful intervention in this condition.

Clinical studies from the past have well documented the effect of cataract extraction (eg, phacoemulsification and extracapsular cataract extraction) on IOP, anterior chamber depth, and angle opening width in the normal eye and in eyes with primary open-angle glaucoma (POAG).^3–6 Studies^3–6 have shown that phacoemulsification alone can effectively lower IOP by 2 to 5 mm Hg in patients with open angles with or without glaucoma. These studies have shown promising results and indicate that cataract extraction may be a powerful tool for IOP management in patients diagnosed with POAG.

The benefit of cataract extraction in eyes with angle closure and, to a lesser extent, occludable angles has also been evaluated and can be a viable treatment option. We identify these conditions and discuss the postoperative effect of cataract removal.

OCCLUDABLE ANGLES

The International Society of Geographical and Epidemiological Ophthalmology have recently identified^7,8 eyes with narrow iridocorneal angles or occludable angles as primary angle-closure suspects. These eyes carry a long-term risk of poor visual outcomes and can be considered in the preglaucomatous stage because of the likelihood for progression to PACG over time.^7,8

Clinically, classification of the angle varies widely and relies on practitioner skill and technique. Gonioscopy remains the gold standard, and for the purposes of this chapter, we will define the angle based on the Shaffer grading system, which describes the relationship between the trabecular meshwork (TM) and iris. With this system, an occludable angle is present if a grading of slit, Grade 1, or Grade 2 is observed (Table 68-1). The presence of appositional closure, peripheral anterior synechiae (PAS), increased segmental TM pigmentation, a history of previous angle closure, anterior chamber depth less than 2 mm, and family history of angle closure also suggest that an angle is occludable and should be identified as such.^9,10

We know that occludable angles carry the risk of progression to angle closure, which can cause extreme elevations in IOP and subsequent irreversible damage to the optic nerve, iris, lens, corneal endothelium, and TM.10 The mechanism of elevated IOP is typically through pupillary block, and therefore, treatment modalities have been targeted to alleviate this event.^11,12 However patients diagnosed with occludable angles typically have not experienced pupillary block, and management of these patients is guided by prevention.

The cornerstone of prophylactic management for angle closure remains LPI. This procedure creates an alternate route for aqueous flow from the posterior chamber into the anterior chamber, allowing the iris to move posteriorly and free the TM from occlusion.¹⁰ The IOP-lowering effect of LPI can be profound in cases of true angle closure and have been shown to significantly increase the angle width and decrease IOP in both angle closure and occludable angles.¹⁴ However, LPI has not been shown to have a significant effect on anterior chamber depth in these patients.¹⁴ Because a shallow anterior chamber depth can predispose an eye to angle closure, this needs to be considered when approaching the patient with potentially occludable angles.

It has been well documented that eyes with occludable angles also have shallower anterior chamber depths when compared to eyes with open angles.^15–17 The shallower anterior chamber depth in this group is due to anatomical predisposition, steeper curvature of the anterior lens surface, narrower chamber angle, more anterior positioned ciliary bodies (plateau iris), more anteriorly located lens, and genetic predetermination.^16–18 In addition, mean intraocular lens (IOL) thickness was also shown to be greater in those eyes with occludable angles when compared to normal eyes.^15,16 The growth of the lens, as occurs in cataract development, leads to a progressive anterior chamber shallowing rate of 0.35 to 0.50 mm in 50 years.¹⁹ Therefore, we know that increasing anteroposterior diameter of the crystalline lens throughout life results in gradual decrease in anterior chamber depth and volume in all eyes.

Cataract extraction alone can lower IOP, increase anterior chamber depth, and widen the angle in normal eyes and those with POAG as mentioned before.^2–6 Patients with occludable angles and lens opacities or visually significant cataracts should be strongly considered as appropriate surgical candidates for cataract extraction. The steeper curvature and anterior position of the crystalline lens in these eyes, which contribute to the risk of angle closure, are easily amenable to surgery with current phacoemulsification and foldable IOL techniques but not LPI. LPI remains the standard of therapy; however, anterior chamber depth is not significantly affected in eyes with occludable angles. LPI also does not address the visual limitations caused by the developing cataract and carries the potential complication for lenticular damage and subsequent cataract development.

The decision to perform cataract extraction on a patient with occludable angles is dependent on the clinical presentation. In these cases, LPI and cataract removal are both intended for the purposes of prophylactic treatment against angle closure. Both can lower IOP and widen the anterior chamber angle; however, cataract removal has a more profound influence on increasing the anterior chamber depth. With the proven benefits of cataract extraction, including improved visual outcomes, this approach may become a standard of care in patients with occludable angles with cataracts or in patients with occludable angles refractory to LPI.

ANGLE CLOSURE

PAC can be categorized into 2 groups: acute primary angle closure (APAC) and chronic primary angle-closure glaucoma (CPACG).⁷ These conditions are characterized by elevated IOP. APAC is considered a common ophthalmic emergency that requires immediate intervention and treatment to prevent glaucomatous optic nerve damage,²⁰ whereas CPACG is the leading cause of blindness in cases of PACG.^21–23 Many treatment modalities are available in approaching patients with these conditions including cataract extraction.

The definitive treatment in PAC, especially in APAC, remains performing an LPI, but this may not be possible in the acute setting. The initial treatment then is aimed at rapidly reducing IOP to alleviate symptoms of pain and prevent further irreversible damage to ocular tissues.11 This is typically achieved with topical IOP-lowering medications, oral acetazolamide, and systemic hyperosmotic agents, such as mannitol. The drawback to these therapies is that they may fail to effectively reduce IOP in many cases, and the systemic medications can have serious systemic side effects.

Anterior chamber paracentesis is also an option in the emergent setting of APAC. Anterior chamber paracentesis offers the advantage of rapid IOP reduction as well as instantaneous symptom relief.²⁴ Rapid IOP control also limits the extent of ocular tissue damage resulting from elevated IOP. APAC typically presents with corneal edema, which can make performing LPI a complex task; however, anterior chamber paracentesis can improve corneal clarity and facilitate laser iridotomy. Anterior chamber paracentesis is limited by its inability to maintain lowered IOP over an extended period of time, and therefore, topical and systemic medications need to be used in conjunction with this procedure. Patients with APAC also tend to present with shallow anterior chambers, which can lead to iris and lens/capsular damage if these structures are breached by a paracentesis knife.²⁴

Argon laser peripheral iridoplasty (ALPI) can also be used to mechanically open up the angle in cases of APAC and has long been used in cases of medically resistant APAC.²⁵ ALPI involves the placement of a ring of contraction burns on the peripheral iris to contract the iris stroma near the angle. This mechanically pulls open the closed angle, allowing aqueous to flow through the TM and reduce IOP. This allows the eye time to become quiet with lowered IOP before definitive treatment with laser iridotomy can be performed.²⁶ ALPI has also been thought to reduce the duration of appositional angle closure and thus the formation of PAS in cases of APAC.²⁷ This would potentially help reduce the risk of progression to CPACG; however, this is outcome is still being investigated.

Once IOP has been controlled in APAC, the goal of treatment is to prevent recurrence of acute attacks and avoid progression to CPACG. The ideal treatment should be aimed at eliminating pupillary block that would prevent future attacks and widening the angle and breaking appositional closure to prevent the development of CPACG. Traditionally, the treatment of choice is LPI. Although this therapy has been shown to reduce elevated IOP and break attacks of APAC, it is unclear whether this prevents recurrence of angle-closure attacks. Moreover, the ability of LPI to prevent progression to CPACG has been shown to be limited. Despite initial success with LPI, some studies have shown that as many as half of these patients go on to develop persistently elevated IOP.²⁸ This can be the result of extensive residual appositional closure, TM damage, formation of PAS as a result of inflammation, or prolonged angle closure during the acute attack.²⁹ With this in mind, alternative treatments need to be identified that address these outcomes.

Evidence suggests the important role of the crystalline lens in angle configuration.^{15–17,19,29,30} The lens can narrow the angle by displacing the peripheral iris anteriorly, a situation that becomes more pronounced in the presence of a cataractous lens. The thickness of a cataractous lens can also contribute to pupillary blockade in predisposed eyes. Therefore, cataracts may be a major contributing factor in angle closure, because many patients presenting with PAC are older and have concomitant cataracts. Cataract extraction as a treatment modality for APAC and CPACG has been widely performed. In PAC, the underlying pathophysiology of elevated IOP is mechanical closure of the angle. Several mechanisms can be involved in angle closure; however, pupillary blockade appears to be the most important inciting incident.¹² The mechanism by which cataract extraction effectively treats PAC is not well understood; however, it is believed that relieving pupillary block and opening the anterior chamber angle play a large role.³¹

As in cases of POAG, cataract extraction offers the benefit of lowering the IOP, increasing the anterior chamber depth, and widening the angle in PAC. A study by Hayashi and colleagues³⁰ found that the width and the depth of the anterior chamber angle in eyes with PACG increased significantly after cataract extraction and IOL implantation and became similar to that in eyes with POAG and in normal eyes. The decrease in IOP seen in the postoperative period may be attributed to these findings. It has been shown that early phacoemulsification with foldable IOL implantation significantly reduces the risk of IOP rise in patients after abortion of APAC when compared to conventional LPI and ALPI.³² As mentioned previously, recurrence of high IOP with LPI seems to be secondary to residual angle closure. Cataract extraction is more effective at dealing with residual angle closure by deepening the anterior chamber, widening the angle, and attenuating the anterior positioning of the ciliary processes.³² This allows for greater aqueous outflow and IOP reduction over a longer period of time.

Another advantage of cataract extraction when compared to LPI and ALPI is the significant difference in the mean number of glaucoma medications needed to control IOP. After cataract extraction, patients with PAC require fewer topical medications than those treated with the laser modalities.³² Also, patients receiving LPI have an increased risk of developing visually significant cataracts, especially posterior subcapsular cataracts, which will ultimately necessitate removal to improve vision.³³

More recently, the Effectiveness of Early Lens Extraction for the Treatment of Primary Angle Closure Glaucoma (EAGLE) trial evaluated individuals affected by PAC in the absence of a cataractous lens. The study compared clear lens extraction in the setting of PAC to outcomes of LPI and medical therapy as first-line intervention. The EAGLE trial has shown that initial treatment with clear lens extraction was superior to LPI plus topical medications for PAC and PACG. It was also shown that the overall health status, visual impairment and disability, and glaucoma-specific disability were all improved despite patients not having visually significant cataracts. From a clinical perspective, clear lens extraction resulted in better IOP reduction when compared to standard care and significantly reduced the need for more invasive glaucoma surgeries as well as glaucoma medications. Visual function was also improved over the standard therapy with better contrast sensitivity as well as correction of refractive error with IOL implantation.34

Although cataract extraction is effective in lowering IOP, widening the angle, and increasing anterior chamber depth, patients with APAC tend to have better IOP outcomes than patients with CPACG. This is thought to be a result of more TM damage and formation of PAS in CPACG.³⁵ The presence of PAS then becomes a confounding variable in determining how effective cataract extraction will be in the long-term control of IOP. It has been suggested by Lai and colleagues³⁶ that the resolution of PAS in PAC after cataract surgery is due to viscodissection as well as positive flushing pressure and suction during lens and cortical removal. In any case, the presence of PAS postoperatively may significantly reduce the effect of cataract extraction on IOP; however, short-term IOP decrease is still significant.

With these considerations in mind, future improvements on treating PAC need to be evaluated. The effect of cataract extraction with implantable IOLs is an effective approach to reducing IOP, increasing anterior chamber depth, and widening the angle in patients with PAC. These postoperative results were significant enough that Gunning and Greve³¹ advocated cataract extraction with IOL implantation alone in the treatment of angle-closure glaucoma, as they found it resulted in IOP reduction to the same extent as traditional glaucoma filtering surgery with fewer complications. This technique has proven advantages over conventional laser therapies, namely LPI. However, cataract extraction in eyes with PAC is much more technically challenging than standard cataract surgery. Poor pupillary dilation, corneal edema, and weakened zonules are just some of the obstacles that a surgeon might face in dealing with PAC. The optimal timing for cataract surgery in these cases remains unclear, and it may be beneficial to quiet the eye with medication and laser prior to intraocular surgery. Goniosynechialysis may also be another effective approach in treating extensive PAS and improving postoperative IOP in patients with both types of PAC as long as the TM is viable. With the advances in phacoemulsification and the relative safety of the procedure, cataract extraction in patients with PAC in the presence or absence of visually significant cataracts is a compelling clinical intervention.

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