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This paper by Wang et al. (1819) contributes unique information of 24-hour intraocular pressure (IOP) profiles in subjects with primary open-angle glaucoma (POAG) identified from a population-based study in Handan, China. This is the first such evaluation of a populationbased sample of newly diagnosed and untreated POAG subjects. Notably, more than 80% of Chinese subjects with untreated POAG in this study had a peak IOP of < 21 mmHg on 24-hour phasing. In unilateral cases, the IOP in the glaucomatous eye was similar to the IOP in the contralateral non-glaucomatous eye. The finding of the majority of POAG patients having IOP within the statistically normal population range has also been reported in several population based studies around the world, and it noteworthy that within Asia, this has been found in Singapore, Japan, Korea, India and China (although none of these involved 24-hour IOP profiles). The strengths of this study were standardized definitions of POAG, strict and meticulous methodology to identify POAG and the 24-hour IOP profiling. The study was limited by almost 30% of POAG subjects not attending the visit for diurnal IOP evaluation, younger age of those who did participate, testing of IOP in the sitting position only, and the fact that participants were all from a rural area in China. The study findings suggest the possible role of non-IOP related risk factors in the pathogenesis of glaucomatous optic neuropathy. Another implication is that there is no obvious cut-off of IOP where glaucoma occurs, and IOP cannot be used as a screening tool for POAG in the general population. Finally these results underscore the need to identify other modifiable risk factors associated with POAG, such as environmental or socioeconomic factors.