The Beijing Angle Closure Progression Study

Inclusion Criteria: * "Static" gonioscopy identifying 6 or more clock hours of angle circumference in which the posterior (usually pigmented) trabecular meshwork cannot be seen in both eyes with no peripheral anterior synechiae, and normal intraocular pressure (IOP), optic nerve and visual field. * Able to provide informed consent Exclusion Criteria: * Any evidence of primary angle closure (a narrow angle as defined above, but with PAS and/or IOP \> 21 mmHg) or primary angle closure glaucoma (visual field defect or glaucomatous optic neuropathy). * Previous intraocular surgery or laser treatment, such as cataract surgery, laser trabeculoplasty, trabeculectomy, laser peripheral iridectomy, and laser iridoplasty * Sign of prior acute attack, such as glaucomatous fleck, keratic precipitates, or iris atrophy. * Anterior segment structural abnormalities shown by examination, such as iris or ciliary body tumor. * Severe health problems precluding follow-up such as end-stage heart disease, kidney disease, or lung disease, or terminal cancer. * Severe eye diseases, such as cataract, macular disease, and retinal detachment.