Lens extraction in primary angle closure.

T he crystalline lens has a pivotal role in primary angle closure (PAC), both in the pathogenesis of pupil block and by exacerbating the effect of non-pupil block mechanisms such as peripheral iris crowding. Eyes with angle closure tend to have shallow anterior chambers and thick, anteriorly positioned lenses when compared with normal eyes. Removing the lens creates more space in the anterior chamber and widens the angle, which may be enough to achieve intraocular pressure (IOP) control. The role of lens extraction as a treatment for angle closure has been debated for many years. But with the knowledge that the lens is the single most important contributing factor to the angle closure process, and having acquired the technology and skills to perform relatively safe small incision cataract surgery, should we now be thinking about performing early lens extraction in angle closure patients with the aim of preventing the development of glaucomatous optic neuropathy at a later stage? In this issue of the BJO (p 14) Tan and co-authors highlight some of the controversies and ethical considerations surrounding the role of early lens extraction in patients with acute angle closure. Theoretically, removing the lens at an early stage will deepen the anterior chamber and open the angle, thus hindering the formation of peripheral anterior synechiae (PAS) and improving the prospects for good long term IOP control. In addition, many of these patients will eventually require surgery for visually significant cataract at some stage. Tan et al report the corrected visual acuity of patients presenting with acute angle closure soon after resolution of the attack. Just over 50% of patients obtained a visual acuity of 6/12 or better at a mean interval of 1.7 days after the acute angle closure episode. Factors such as corneal oedema may still be contributing to reduced visual acuity so soon after an attack and one would expect the vision to improve even more over a longer follow up period. The authors think that with this degree of improvement in visual acuity following an acute attack it may not be justifiable to propose primary lens extraction instead of iridotomy as treatment for acute angle closure. Any discussion of early lens extraction does not in any way imply that ophthalmologists should deviate from current protocols for the management of this potentially blinding condition. All patients presenting with acute angle closure should be treated immediately with systemic and topical medications to lower the IOP, followed by laser iridotomy for the affected and fellow eyes. However, Asian patients who present with acute angle closure can take longer to respond to medical treatment and may require additional interventions such as argon laser peripheral iridoplasty to break the acute attack before performing laser iridotomy. 9 In the follow up period after an acute attack of angle closure a substantial proportion of Chinese Singaporean subjects develop chronic elevation of IOP and glaucomatous optic nerve damage. Possible explanations for these findings include delayed initial presentation, a greater role for nonpupil block mechanisms in Asian patients with PAC and the presence of pre-existing asymptomatic primary angle closure glaucoma (PACG) before the acute attack.