Br J Ophthalmol 86(2): 238-242

The definition and classification of glaucoma in prevalence surveys

^{Department of Epidemiology and International Eye Health, Institute of Ophthalmology, Bath Street, London EC1V 9EL, UK}

^{University of Ottawa Eye Institute, Ottawa, Ontario, Canada}

^{Dana Center for Preventive Ophthalmology, Johns Hopkins University, Baltimore, Maryland, USA}

Correspondence to:
Paul J Foster, Department of Epidemiology and International Eye Health, Institute of Ophthalmology, Bath Street, London EC1V 9EL, UK;
ku.ca.lcu@retsof.p

Accepted 2001 Aug 3.

Abstract

This review describes a scheme for diagnosis of glaucoma in population based prevalence surveys. Cases are diagnosed on the grounds of both structural and functional evidence of glaucomatous optic neuropathy. The scheme also makes provision for diagnosing glaucoma in eyes with severe visual loss where formal field testing is impractical, and for blind eyes in which the optic disc cannot be seen because of media opacities.

Keywords: glaucoma, prevalence surveys

Abstract

An appropriate case definition is the keystone of epidemiological research whether measuring prevalence, studying risk factors, or conducting clinical trials. This reconsideration of the definition and classification of glaucoma was prompted by our experiences of cross sectional prevalence research in Africa and Asia, and by the difficulty we experienced in identifying and classifying cases and in making valid comparisons with previously published data. The proposed definition of glaucomatous optic neuropathy has evolved from one initially developed for the Kongwa Eye Study in Tanzania.¹ At the same time, work in Mongolia and Singapore,^2,³ where there was a high prevalence of primary angle closure glaucoma (PACG), had prompted a re-examination of the definition of this condition. We were concerned that in previous reports subjects with “latent angle closure glaucoma” had been classified as cases of established glaucoma, despite having normal visual function. This may result in misinterpretation of the estimates of visual morbidity attributable to glaucoma, especially as PACG is believed to be at least as prevalent as primary open angle glaucoma (POAG).⁴

At the biennial congress of the International Society for Geographical and Epidemiological Ophthalmology held in Leeuwenhorst, the Netherlands, in June 1998, a group interested in glaucoma epidemiology met to discuss the prototype system. This has since been discussed further, and various experts in the fields of glaucoma research and clinical practice consulted. (The appendix lists participants and co-opted advisers.) The views presented here are, however, those of the authors. Our aim has been to present a practical framework which can be tested and discussed further.

Acknowledgments

We thank all those mentioned in the appendix for participating in this work, and wish to emphasise that the views expressed in this manuscript are solely those of the authors, and not those of the ISGEO or an other organisation or individual.

Acknowledgments

Abbreviations

PACG, primary angle closure glaucoma
POAG, primary open angle glaucoma
VCDR, vertical cup:disc ratio
IOP, intraocular pressure
PAC, primary angle closure
PAS, peripheral anterior synechiae

Abbreviations

APPENDIX

ISGEO Glaucoma classification working group, 27 and 28 June 1998, Leeuwenhorst, Netherlands: co-chair: Gordon J Johnson, Harry A Quigley; rapporteurs: Ralf Buhrmann, Paul J Foster; group members: Poul-Helge Alsbirk, Michelle Coffey, Lalit Dandona, Paulus TVM de Jong, Fridbert Jonasson, Paul Mitchell, Ian Murdoch, R Pararajasegaram, RS Ramrattan, Poul Roux, Ravi Thomas, Bjorn Thylefors, Roger Wolfs; co-opted advisers: Anders Heijl, David Henson, Roger A Hitchings, Chris A Johnson, Gottfried Naumann, John F Salmon; co-authors of studies from which data are presented: Bangladesh: M Rahman, N Rahman, AU Zahman, A Zia; Mongolia: J Bassanhu, J Devereux, D Uranchimeg, PS Lee, D Machin; Singapore: SKL Seah, F Oen, TP Ng, D Machin, J Devereux, J Hall, J Hee, SJ Chew, PT Khaw; Tanzania: Y Barron, SK West, MS Oliva, BBO Mmbaga.

APPENDIX

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