The Role of Lens Extraction in Primary Angle-Closure Glaucoma

Introduction

Primary angle-closure glaucoma (PACG) is a form of glaucoma caused largely by ocular hypertension secondary to closure, apposition or synechia, of the anterior chamber drainage angle. PACG eyes have a characteristically shallow anterior chamber, which is in turn the result of a thick, anteriorly positioned lens. Removal of the lens, or the cataract, in PACG eyes is known to reverse the anatomical predisposition to angle closure. The role of lens or cataract extraction in PACG has attracted interest in recent years as one of the possible surgical options in PACG eyes, especially in situations when the surgeon and/or patient are keen to avoid the potential complications of glaucoma surgeries.

Principles of Treatment in PACG

The initial management of PACG aims at opening up all appositionally closed portions of the drainage angle. As pupillary block is an important mechanism of angle closure in the vast majority of PACG eyes, laser peripheral iridotomy is usually the first line of treatment, except in those eyes where very extensive peripheral anterior synechiae (PAS) is already present. After iridotomy, if there is still extensive appositional angle closure and raised intraocular pressure (IOP), argon laser peripheral iridoplasty (ALPI) may be considered. Earlier lens or cataract extraction may also be considered, and this will be discussed further in the rest of this chapter. An ongoing randomized controlled interventional trial (EAGLE Study) compared clear lens extraction versus laser peripheral iridotomy in newly diagnosed PACG eyes without cataract. It would be interesting to see whether clear lens extraction could replace iridotomy in these eyes when the results are published.

If the IOP remains unsafe after all attempts to re-open the angle, topical anti-glaucomatous medications should be started and titrated according to the IOP levels. Further surgical treatments might be considered when IOP control remains suboptimal despite maximally tolerated medications. Further surgical treatments may include trabeculectomy, goniosynechialysis (GSL), trabeculotomy, glaucoma drainage device (GDD) implantation, and cyclodestructive procedures by laser or cryotherapy. These procedures could be performed in isolation, or in combination with lens/cataract extraction.

Biometry of PACG Eyes

PACG eyes have unique biometric properties that might explain the role of lens extraction in its management. Studies in the 1970s–1980s have found significantly shallower anterior chamber ( Fig. 103-1 ), with narrower drainage angles in PACG eyes. The lens is also thicker with steeper anterior lens surface, and overall more anteriorly positioned, compared to control. Lin et al. also compared acute primary angle-closure (APAC) eyes with controls and concluded that an anterior chamber depth (ACD) of <2.70 mm was the most sensitive (94%) and specific (94%) parameter to differentiate APAC eyes from normal controls.