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Editors Selection IGR 20-3

Epidemiology: Incidence of glaucoma in the Handan Eye Study

Comment by Rupert Bourne on:

104628 Five-year incidence of primary glaucoma and related risk factors - The Handan eye study, Zhang Y; Hao J; Zhang Q et al., Acta Ophthalmologica, 2023; 101: e50-e60

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There are relatively few studies that have reported incidence of primary glaucoma, and this article by Zhang et al. is the first such study in China. The Handan Eye Study was a population-based eye survey of adults aged ≥ 35 years conducted in rural northern China between 2006 and 2007, and the follow-up study (2012-2013) sought to determine incident cases of glaucoma that were not present at baseline using standardized protocols. 85% of those examined at baseline and who were still alive, were subsequently reviewed (5,394 participants) which is remarkably high for a population-based cohort study. Eighty-two subjects were diagnosed with newly incident primary glaucoma, half on the basis of optic disc appearance and half on the basis of disc and visual field changes. This equates to an age- and gender-standardized five-year incidence of 2.1% among those aged ≥ 40 years, an annual incidence of 0.4%. This was similar to the Ponza Eye Study (Italy),¹ but higher than that reported in South Korea,² Singapore (Indians),³ and Israel (0.2%).⁴ Although an extrapolation of a single study's findings to the national population of China should be interpreted with caution, the authors estimate that, annually, approximately 2.97 million people aged ≥ 40 years will develop primary glaucoma. These data will undoubtedly contribute to the planning of glaucoma services in China, which is now in its 14^th five year national eye health plan (2021-25), and where significant improvements in equity and accessibility of eye care services have been achieved.

Interestingly, 88% of incident glaucoma cases were not diagnosed before the follow-up examinations although 14 participants were visually impaired (ten with low vision and four were blind in at least one eye). The authors comment that the high rate of undiagnosed glaucoma was likely related to the rural location of the Handan Eye Study population, in which 89% of subjects reported never experiencing eye care. Other intriguing findings from this meticulously-conducted study included the finding that 90% of incident primary glaucoma cases had an intraocular pressure below 21 mmHg, and that a baseline vertical cup/disc ratio (VCDR) of ≥ 0.6 yielded the strongest association with incident primary glaucoma, with a risk 5.3 times higher relative to VCDR < 0.60. Both findings are important considerations in the context of screening for glaucoma.

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