Most patients have primary glaucoma. Intraocular atrial fluid, produced by the ciliary bulge of the ciliary body, flows into the anterior chamber through the pupil and is then discharged through the trabecular meshwork of the anterior chamber angle. Depending on the width of the anterior chamber angle, there are open angle glaucoma and closed angle glaucoma. In closed-angle glaucoma, IOP is elevated because the narrow atrial angle causes the surface of the atrial drainage canal to be blocked by the peripheral iris, much like the surface of a drain in a washing sink is completely covered by a plastic sheet. In this type of person, the angle between the iris and cornea of the eye is not as large or open as normal (narrow angle), and this narrow atrial angle can be inherited, so it runs in families. This type of glaucoma mostly presents as acute glaucoma. Open-angle glaucoma is caused by a blockage in the atrial drainage duct. The blockage occurs inside the drainage duct, just as a blockage in a washing sink occurs inside the drainage duct. This type of glaucoma mostly presents as chronic glaucoma.