Re: Tham et al.: Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis (Ophthalmology 2014;121:2081-90)

We read with interest the article by Tham et al.1Tham Y.C. Li X. Wong T.Y. et al.Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis.Ophthalmology. 2014; 121: 2081-2090Abstract Full Text Full Text PDF PubMed Scopus (3338) Google Scholar The authors strive to provide an "accurate estimation of the current glaucoma prevalence and future projections of the number of people with glaucoma" based on existing literature. Regarding angle-closure glaucoma (ACG) in non-Asian populations, we would like to opine that this is very difficult to estimate at present, owing to the meager amount and quality of available data. This fact was not highlighted by the authors. The authors scanned the available literature for quality prevalence studies, and included subsequently in this review only 7 publications that provide ACG prevalence rates in non-Asians (references 56, 60, 61, 66, 68, 69, and 72). These extend from 0.009% (West Ireland, reference 56) to 0.97% (Italy, reference 61) and therefore likely reflect a methodologic inconsistency. For example, if angle closure is defined as "equal to or less than grade II" (61) rather than the more accepted criterion requiring some degree of iridocorneal contact, then ACG is going to be overdiagnosed greatly. Conversely, considering the variable technique and subjective interpretation of gonioscopy, ACG may be underdiagnosed. For example, we and other investigators have shown that if angle examination is done in conditions of strong light in the examining room and/or slit lamp, an otherwise appositionally closed angle can be misdiagnosed as open.2Barkana Y. Dorairaj S.K. Gerber Y. et al.Agreement between gonioscopy and ultrasound biomicroscopy in detecting iridotrabecular apposition.Arch Ophthalmol. 2007; 125: 1331-1335Crossref PubMed Scopus (57) Google Scholar, 3Mishima K. Tomidokoro A. Suramethakul P. et al.Iridotrabecular contact observed using anterior segment three-dimensional OCT in eyes with a shallow peripheral anterior chamber.Invest Ophthalmol Vis Sci. 2013; 54: 4628-4635Crossref PubMed Scopus (12) Google Scholar As another example, an examiner can mistakenly record seeing the pigmented trabecular meshwork, where in reality what is visualized is linear pigment deposition more anteriorly; angle closure is thus missed and underdiagnosed (the true trabecular meshwork can be revealed and this mistake can be avoided only when employing dynamic corneal indentation with the gonio-lens). Because, in some population studies, very few subjects are diagnosed with ACG, missing even a few cases might significantly skew the reported rate. A small study by one of us seems to suggest that published figures of 0.6% (reference 60) or 0.7% (reference 72) are closer to the true prevalence rate.4Barkana Y. Dekel I. Goldich Y. et al.Angle closure in Caucasians–a pilot, general ophthalmology clinic-based study.J Glaucoma. 2012; 21: 337-341Crossref PubMed Scopus (9) Google Scholar The answer awaits a modern prevalence study that, in addition to incorporating good gonioscopic technique, includes objective angle grading using an imaging device. In some studies, it has been reported that when imaging devices are used to diagnose angle closure, rates are higher compared with gonioscopy.3Mishima K. Tomidokoro A. Suramethakul P. et al.Iridotrabecular contact observed using anterior segment three-dimensional OCT in eyes with a shallow peripheral anterior chamber.Invest Ophthalmol Vis Sci. 2013; 54: 4628-4635Crossref PubMed Scopus (12) Google Scholar, 5Sakata L.M. Lavanya R. Friedman D.S. et al.Comparison of gonioscopy and anterior segment ocular coherence tomography in detecting angle closure in different quadrants of the anterior chamber angle.Ophthalmology. 2008; 115: 769-774Abstract Full Text Full Text PDF PubMed Scopus (188) Google Scholar Even with the great respect we all hold for clinical examination, this would provide objective measurement and diagnosis, similar to using a laser cell flare meter for measurement and/or diagnosis in studies of uveitis, or using OCT rather than slit-lamp examination in studies of measurement and/or diagnosis of macular edema. Global Prevalence of Glaucoma and Projections of Glaucoma Burden through 2040: A Systematic Review and Meta-AnalysisOphthalmologyVol. 121Issue 11PreviewGlaucoma is the leading cause of global irreversible blindness. Present estimates of global glaucoma prevalence are not up-to-date and focused mainly on European ancestry populations. We systematically examined the global prevalence of primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG), and projected the number of affected people in 2020 and 2040. Full-Text PDF Author replyOphthalmologyVol. 122Issue 7PreviewWe thank the authors for their valuable comments and suggestions. We agree with the first comment that accurate determination of the prevalence estimates of primary angle-closure glaucoma (PACG) in non-Asian populations is challenging, particularly for North America, Latin America, and Europe. This is mainly owing to the limited PACG prevalence data available in these regions. We would like to clarify that we included a total of 15 publications with PACG data available from non-Asian populations in our systematic review as opposed to 7 publications suggested by the authors (see Fig 2B). Full-Text PDF