What is glaucoma?
Glaucoma is a disease of the optic nerve, a structure that connects the eye to the brain. The nerve is composed of 1.2 million fibers that originate in the retina. If the optic nerve is damaged from any cause, visual signals from the eye cannot reach the brain, leading to vision loss.
In glaucoma, the optic nerve fibers degenerate over time. The nerve then remodels, or changes shape, as the tissue is lost – this process is called "cupping." These nerve changes occur in characteristic patterns which are distinct from other optic nerve diseases and can be identified during a dilated eye exam. Uncontrolled glaucoma is a progressive disease characterized by increased cupping over time.
Progression of optic nerve cupping in a patient with glaucoma. The left panel shows a relatively normal nerve. The arrow is pointing to the cup (shaded yellow). Five years later, the cup has enlarged, a characteristic sign of glaucoma.
In general, the fibers that are responsible for peripheral vision are affected first, and those maintaining central vision are affected late in the disease. As a result, most people with glaucoma will maintain vision straight ahead in at least one eye. Unfortunately, people may not notice changes in their peripheral vision in their everyday life, and so they may be unaware of a problem until they already have advanced damage.
Simulation of glaucomatous visual field loss. Notice that in addition to peripheral vision loss, there is a loss of contrast and wash out of colors with glaucoma.
The optic nerve is an extension of the brain - like the brain and spinal cord, the optic nerve does not regenerate. As a result, any vision lost secondary to optic nerve damage is permanent. This is why early detection and treatment are absolutely essential for preventing blindness from glaucoma.