Editorial

Angle closure and the lens

In cold environments there may be an evolutionary selec-tion advantage to having a shallow anterior chamber: thewarm, vascularized iris in approximation to the corneamay prevent corneal freezing.1 Circumstantial evidenceindicates that shallow anterior chambers may have evolvedin people living in North-east Asia during the last Ice Age.2

Unfortunately, the descendants of these people, particu-larly the Inuit and east Asians are predisposed to primaryangle-closure glaucoma (PACG) in later life.2 Althoughless common in white people, the more one looks, themore one finds.3 Although the clinical outcome of acuteangle closure is generally favourable when treated in atimely manner,4 if treatment is not readily available then itis visually devastating. In central Myanmar it accounts forhalf of the angle-closure blindness, with most eyes havingno perception of light.5 It is estimated that PACG accountsfor about half of the world’s glaucoma-related blindness;6

about 90% are east Asian.6ceo_2393 3..4

In 2002, The International Society for Geographical andEpidemiological Ophthalmology published definitions ofglaucoma to improve consistency amongst epidemiologicalstudies.7 These definitions have infiltrated clinical practice.The term ‘glaucoma’ is reserved for those with glaucoma-tous optic neuropathy (GON).7 Those eyes with iridocor-neal angles traditionally described as ‘occludable’ aretermed primary angle closure suspects (PACS) and thosemeeting criteria for PACS but with peripheral anteriorsynechiae and without GON have primary angle closure(PAC).7 These conditions are considered to representpreglaucomatous stages in the natural history of PACG,and reflect the long-term risk of visual morbidity.8,9

Several factors, including age, female gender and ashallow anterior chamber depth are recognized as riskfactors for PACG, but most of the data supporting theseassociations are clinic based. Population-based data areconflicting about risk factors for PACG. Few population-based studies have included both gonioscopy andocular biometry, and the relatively low prevalence ofangle closure in most populations has meant that multi-variate analyses of proposed risk factors could not be per-formed. However, the most consistently reported riskfactor for PACG is anterior chamber depth. Intuitively,lens thickness should be a risk factor for PACG, but thedata on this issue, surprisingly, fail to support thisnotion.

The lack of association of angle closure with lens thick-ness is an interesting finding, and has been reported inseveral studies.10–12 Although the number of studies islimited, to my knowledge, lens thickness has never beenfound to have an association with angle closure in any

study (clinic- or population-based) which has excludedsubjects with acute angle closure in the analyses. Toexplain the lack of association with lens thickness, it ispossible that there is a disconnection between the axiallens thickness (measured in the studies) and the peripherallens thickness (which is not measured). Two recentpopulation-based studies have reported an intriguingassociation between nuclear cataract and angle closure,independent of age or lens thickness.10,13 To my knowl-edge, the effect of nuclear cataract on lens morphology hasnever been reported.

Despite the lack of association with lens thicknessper se, there is overwhelming clinical evidence that, inthe absence of synechial angle closure, cataract extractionopens the angle. Hence, cataract extraction provides theopportunity to potentially ‘kill two birds with one stone’,restoring vision and eliminating a narrow angle. Gener-ally, this latter effect is considered as a ‘bonus’ and doesnot affect the primary surgical decision, which is based onmanagement of the visually significant cataract. If there isa narrow angle, but no cataract then the clinical decisionfocuses on the risk/benefit profile of treatment. Most eyeswith early angle-closure disease do not progress overa 5-year period,8 but approximately 30% of eyes withPAC will progress to PACG over the same period (upperlimit of the 95% confidence interval at 45%).8 Generally,the recommended first-line treatment for angle-closuredisease is a laser iridotomy ‘to remove any element ofpupil block’. This successfully opens the angle in mostAsian14–16 and white people’s eyes.17 Serious complica-tions are possible, but rare. Hence, the clinician mustdecide whether a laser iridotomy is warranted in anygiven individual. Gonioscopy (both static and dynamic) isa critical component of the clinical assessment. If cataractsurgery is not planned, my approach is to recommend thatmost eyes with PACS and nearly all eyes with PACreceive an yttrium–aluminum–garnet laser iridotomy aspart of the management.

What about the role of clear lens extraction in angle-closure disease? In this issue, Walland and Thomasprovide a comprehensive review on this subject.18 Theauthors stress that any secondary advantage of cataractsurgery in widening the angle in an eye with angle closureis not contentious, but they make the case that clear lensextraction is difficult to justify in terms of its risk/benefitprofile. They point out that clear lens extraction as treat-ment for PAC or PACG is ‘dependent on the extent of anysynechial closure, and may not obviate the need for trab-eculectomy, particularly in medically uncontrolled angleclosure glaucoma’. They provide food for thought with the

Clinical and Experimental Ophthalmology 2011; 39: 3–4 doi: 10.1111/j.1442-9071.2010.02393.x

© 2011 The AuthorsClinical and Experimental Ophthalmology © 2011 Royal Australian and New Zealand College of Ophthalmologists

comment that ‘The mere existence of a very good operationis not an indication for surgery’.

Robert J Casson DPhil FRANZCOSouth Australian Institute of Ophthalmology and

Adelaide University, Adelaide, South Australia, Australia

REFERENCES

1. Alsbirk PH. Primary angle-closure glaucoma. Oculo-metry, epidemiology, and genetics in a high riskpopulation. Acta Ophthalmol Suppl 1976; 127: 5–31.

2. Casson RJ. Anterior chamber depth and primaryangle-closure glaucoma: an evolutionary perspective.Clin Experiment Ophthalmol 2008; 36: 70–7.

3. Ng WS, Ang GS, Azuara-Blanco A. Primary angleclosure glaucoma: a descriptive study in ScottishCaucasians. Clin Experiment Ophthalmol 2008; 36: 847–51.

4. Tan AM, Loon SC, Chew PT. Outcomes followingacute primary angle closure in an Asian population.Clin Experiment Ophthalmol 2009; 37: 467–72.

5. Casson RJ, Newland HS, Muecke J et al. Prevalenceand causes of visual impairment in rural myanmar: theMeiktila Eye Study. Ophthalmology 2007; 114: 2302–8.

6. Quigley HA, Broman AT. The number of people withglaucoma worldwide in 2010 and 2020. Br J Ophthalmol2006; 90: 262–7.

7. Foster PJ, Buhrmann R, Quigley HA, Johnson GJ. Thedefinition and classification of glaucoma in prevalencesurveys. Br J Ophthalmol 2002; 86: 238–42.

8. Thomas R, George R, Parikh R, Muliyil J, Jacob A.Five year risk of progression of primary angle closuresuspects to primary angle closure: a population basedstudy. Br J Ophthalmol 2003; 87: 450–4.

9. Thomas R, Parikh R, Muliyil J, Kumar RS. Five-yearrisk of progression of primary angle closure to primaryangle closure glaucoma: a population-based study. ActaOphthalmol Scand 2003; 81: 480–5.

10. Casson RJ, Marshall D, Newland HS et al. Risk factorsfor early angle-closure disease in a Burmese popula-tion: the Meiktila Eye Study. Eye (Lond) 2009; 23:933–9.

11. Salmon JF. Predisposing factors for chronic angle-closure glaucoma. Prog Retin Eye Res 1999; 18: 121–32.

12. Vijaya L, George R, Arvind H et al. Prevalence of angle-closure disease in a rural southern Indian population.Arch Ophthalmol 2006; 124: 403–9.

13. Xu L, Cao WF, Wang YX, Chen CX, Jonas JB. Anteriorchamber depth and chamber angle and their associa-tions with ocular and general parameters: the BeijingEye Study. Am J Ophthalmol 2008; 145: 929–36.

14. Nolan W, Foster P, Devereux J, Uranchimeg D,Johnson G, Baasanhu J. YAG laser iridotomy treat-ment for primary angle closure in east Asian eyes. Br JOphthalmol 2000; 84: 1255–9.

15. Thomas R, Arun T, Muliyil J, George R. Outcome oflaser peripheral iridotomy in chronic primary angleclosure glaucoma. Ophthalmic Surg Lasers 1999; 30: 547–53.

16. Li S, Wang H, Hu D et al. Prospective evaluation ofchanges in anterior segment morphology after laseriridotomy in Chinese eyes by rotating Scheimpflugcamera imaging. Clin Experiment Ophthalmol 2010; 38:10–14.

17. Ang GS, Wells AP. Changes in Caucasian eyes afterlaser peripheral iridotomy: an anterior segment opticalcoherence tomography study. Clin Experiment Ophthal-mol 2010; 38: 778–85.

18. Walland M, Thomas R. Role of clear lens extraction inadult angle closure disease. Clin Experiment Ophthalmol2011; 39: 61–4.

4 Editorial

© 2011 The AuthorsClinical and Experimental Ophthalmology © 2011 Royal Australian and New Zealand College of Ophthalmologists