A 50-year-old black man was noted to have a large cup-to-disc ratio during a funduscopic examination by his primary care provider (Figure 20-1). The patient reported no visual complaints. Further evaluation revealed elevated intraocular pressure and early visual field defects. He was started on medication to lower his intraocular pressure. He remained asymptomatic, and his visual field defects did not progress for the next several years.
Glaucoma is a leading cause of blindness in the United States and globally. Open-angle glaucoma is an acquired loss of retinal ganglion cells characterized by either normal or increased intraocular pressure (IOP), a large cup-to-disc ratio, and visual field defects. Open-angle glaucoma is treated by reducing IOP, most commonly with eye drops. Angle-closure glaucoma, which is much less common, is an acute increase in IOP from a mechanical obstruction that must be treated emergently to preserve vision.
In 2013, an estimated 65 million people worldwide had glaucoma.1
The prevalence of glaucoma in the global population between ages 40 and 80 is 3.54%; Africa has the highest prevalence of open-angle glaucoma (4.2%); Asia has the highest prevalence of angle-closure glaucoma.1
The incidence of primary open-angle glaucoma was 8.3 per 100,000 population in people older than 40 years in a Minnesota population study.2
According to a population-based study, a family history of glaucoma increased the risk of having glaucoma (odds ratio [OR] = 3.08).3
ETIOLOGY AND PATHOPHYSIOLOGY
Glaucoma pathophysiology is incompletely understood, but the level of IOP correlates with the acquired loss of retinal ganglion cells and resulting irreversible vision loss.4
The ciliary body secretes aqueous humor, which drains through the trabecular meshwork and/or the uveoscleral outflow pathway; the balance between secretion and outflow determines IOP.4
In open-angle glaucoma, resistance in the trabecular meshwork impedes outflow
In angle-closure glaucoma, the drainage pathways is obstructed
High systemic blood pressure affects ocular circulation and is associated with glaucoma progression.5
IOP can cause mechanical stress on the posterior structures of the eye, with consequent damage to optic nerve fibers.4
Optic nerve atrophy is seen as optic disc cupping and irreversible visual field loss. Compare Figures 21-1 and 21-2 to see the difference between abnormal (Figure 21-1) and normal (Figure 21-2) optic disc cupping.
A 50-year-old man with glaucoma has an increased optic cup-to-disc ratio of 0.8. Median cup-to-disc ratio is 0.2 to 0.3, but varies considerably among individuals. (Reproduced with permission from Paul D. Comeau.)
Normal eye with a normal cup-to-disc ratio of 0.4. A cup-to-disc ratio of more than 0.5 requires further evaluation. (Reproduced with permission from Paul D. Comeau.)