Glaucoma and intraocular pressure in EPIC-Norfolk Eye Study: cross sectional studyBMJ 2017; 358 doi: https://doi.org/10.1136/bmj.j3889 (Published 13 September 2017) Cite this as: BMJ 2017;358:j3889
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The recent article by Chan et al provides important data on glaucoma and intraocular pressures in the Norfolk population. However, we would like to highlight a few aspects, which we believe are important in evaluating this information.
The European Prospective Investigation of Cancer (EPIC) study collected ophthalmic data from 8623 participants from 2004-2011.1 It included data on the prevalence and characteristics of glaucoma, and intraocular pressure (IOP) measurements.1
Firstly, we note the ethnic proportions of this cohort to be reported as ‘99.4 white, compared with 96.5% and 87.2% respectively, in Norfolk and the UK’.1 Data from the 2011 census revealed major UK cities including London, Birmingham and Manchester to have considerably lower white British population (45%, 53.1% and 59.3% respectively).2 We believe the disparity between the ethnic demographics reported with other large UK cities may lead to erroneous assumptions of the prevalence of glaucoma in several communities, particularly the number of cases of angle closure glaucoma which has been reported to be less prevalent in Caucasian populations.2 Therefore, it should be emphasised that the data in this study is relevant to the British population in Norfolk and should be used with caution in future planning in terms of resources and research for the remainder of the nation.
Secondly, of the 363 patients (4.2%) reported as having a diagnosis of glaucoma, it is further clarified that 244 patients had a prior diagnosis of this condition, with 66.3% of the cases primary open angle glaucoma being previously known. The mean cohort IOP is reported as 16.3mmHg and the mean for glaucomatous eyes 16.7mmHg. For the latter group, it is unclear whether the mean IOP was calculated using measurements during this study or from prior consultations where a diagnosis of glaucoma was initially made. It is also not specified if there was concurrent use of intraocular pressure lowering medications. The reported figure for mean IOP may therefore be misleadingly low and lessen the assumption that IOP was not a sensitive or specific indicator of glaucoma that was made in the study.
1. Chan, MPY et al. Glaucoma and intraocular pressure in EPIC- Norfolk Eye Study: cross sectional study. BMJ 2017;358:j3889
2. Office for National Statistics; National Records of Scotland ; Northern Ireland Statistics and Research Agency (2016): 2011 Census aggregate data. UK Data Service (Edition: June 2016).
3. Yip JL, Foster PJ. Ethnic differences in primary angle-closure glaucoma. Current Opinion in Ophthalmology. 2006 Apr;17(2):175-80.
Competing interests: No competing interests