PurposeTo determine the 10-year incidence of all forms of primary angle closure (PAC) in phakic eyes and its risk factors in an urban Chinese population aged 50 years and older.MethodsSurvivors of 1405 baseline participants were invited to attend the 10-year follow-up visit in the Liwan Eye Study. Participants with established baseline angle closure, including primary angle closure suspects (PACS), PAC and primary angle closure glaucoma (PACG), or those who underwent bilateral cataract surgery during the 10-year period, as well as those who did not tolerate gonioscopic examinations, were excluded from this analysis. Incident PAC was present when those with open angles at baseline developed angle closure in any form in either eye during the 10-year period.ResultsAmong 791 participants who returned during the 10-year follow-up visit, 620 (78.4%) provided data on PAC incidence. The 10-year cumulative incidence of any forms of PAC was 20.5% (127/620, 95% CI 17.4% to 24.9%), including 16.9%, 2.4% and 1.1% with incident PACS, PAC and PACG in either eye, respectively. In multiple logistic regression, significant risk factors for incident angle closure were greater baseline lens thickness (OR=1.82 per mm, p=0.003), shallower anterior chamber depth (OR=3.18 per mm decreased, p=0.010) and narrower angle width (OR=1.63 per decreased angle width, p<0.0001).ConclusionsApproximately one in five people aged 50 years and older developed some form of angle closure over a 10-year period. Small ocular dimensions and hyperopia at baseline were associated with the development of angle closure.