The glaucoma syndromes are divided into two main groups: primary and secondary. The primary glaucomas are those for which the cause of increased resistance to outflow and elevated intraocular pressure (IOP) is unknown. The secondary glaucomas are associated with known ocular or systemic conditions responsible for the elevated IOP and resistance to outflow. Primary open-angle glaucoma is the most common form of glaucoma in the United States. It constitutes about two-thirds of all cases of glaucoma. This particular disease is probably the final common pathway for a variety of yet undistinguished separate pathophysiologic processes. As our understanding of the genetic and pathophysiologic components continues to expand, I predict that we will eventually distinguish several other conditions with these characteristic optic nerve and visual field defects.

To date, our best understanding is that the damage and functional loss from glaucoma are caused by some combination of a sensitivity to barotrauma of retinal ganglion cell axons at the lamina cribrosa and a relative elevation of IOP, for example, a relative IOP increase as a result of aging and senescence of the drainage system— (1) children never have ocular hypertension (adjusted for central corneal thickness-induced measurement artifact) as a normal state and (2) even in low-tension glaucoma, the lowering of IOP reduces the progression of optic nerve and visual field damage.