Primary Open-Angle Glaucoma

The overriding fundamental distinction is between open-angle and angle-closure glaucomas. These are both often called primary when there is no apparent ocular or systemic cause and secondary when there is an identifiable initiating ocular or systemic mechanism. Because there is likely more than one mechanism of primary open-angle glaucoma (POAG), the disease entity should likely be termed the POAGs. (Similarly, primary angle-closure glaucoma is usually due to pupillary block, but plateau iris, an uncommon condition, is also often called a form of primary angle-closure glaucoma.) In some ways, these terms are not that important except for clinical categorization, because they reflect that we understand some mechanisms but not others. For example, it is common for a patient with apparent POAG to later be discovered to have pseudoexfoliation, at which time the diagnosis is changed to that of a secondary open-angle glaucoma (because we believe we now understand the mechanism of that glaucoma; see Chapter 21).