Glaucoma is a disease of the optic nerve, which connects the eye with the brain and carries visual information. Although there are many risk factors for glaucoma, among the most significant is elevated intraocular pressure. According to our current understanding, optic nerve damage in glaucoma develops when the intraocular pressure is at a level the eye cannot tolerate. Importantly, some eyes may develop damage at relatively low intraocular pressures whereas other eyes may not develop damage at relatively high intraocular pressures. Therefore, the appropriate intraocular pressure to avoid damage varies among patients and may even vary during the course of one’s life.
Broadly, glaucoma may be classified as either open or closed angle glaucoma. Anatomically, the cornea and iris form an angle called the anterior chamber angle. The eye is an enclosed space with both a fluid pump, called the ciliary body, and a drainage apparatus, called the trabecular meshwork. The drainage apparatus is located at the apex of the anterior chamber angle. In closed angle glaucoma the anterior chamber angle is narrow. If the anterior chamber angle is sufficiently tight to restrict the flow of fluid to the drainage apparatus of the eye, the intraocular pressure rises. This elevation of intraocular pressure may ultimately lead to optic nerve damage from glaucoma. However, glaucoma may also occur when there is no restriction of fluid flow to the drainage apparatus. In this circumstance, fluid flows properly to the drains of the eye, but the drain itself malfunctions and causes increased intraocular pressure and optic nerve damage from glaucoma. Elevated intraocular pressure despite an open anterior chamber angle is called open angle glaucoma. Within the categories of open and closed angle glaucoma are many subtypes of glaucoma.
Typically, there is no single test that makes the diagnosis of glaucoma. Diagnosis and classification of glaucoma is based on information from many different tests and findings. The features of glaucoma include: identifiable damage to the optic nerve in a characteristically glaucomatous pattern and loss of vision in particular areas of the visual field (the visual field is everything one may see without moving the eye). Risk factors for glaucoma include: elevated intraocular pressure, increasing age, race, family history of glaucoma, and thin central corneal thickness.