Glaucoma is the 3rd leading cause of blindness worldwide according to the Glaucoma Foundation and is a categorical name for a group of eye diseases that damage the optic nerve and cause vision loss, often with few or no symptoms. The optic nerve is part of the back of the eye and it is a bundle of nerve fibers that carry visual messages to the brain.
Two different forms of glaucoma can occur: open-angle glaucoma or angle-closure glaucoma. Open-angle glaucoma is the most common form of glaucoma, affecting about 3 million Americans. It occurs when the eye's drainage canals become clogged over time. The inner eye pressure (also called intraocular pressure or IOP) rises because the correct amount of fluid is not able to drain out of the eye. With open-angle glaucoma, the entrances to the drainage canals are clear and should be working correctly. The clogging problem occurs inside the drainage canals, like clogging that can occur inside a pipe below a drain in a sink.
Angle-closure glaucoma is also known as acute glaucoma or narrow angle glaucoma. It is much more uncommon and is very different from open-angle glaucoma in that the eye pressure usually goes up very fast. This takes place when the drainage canals get blocked or covered, like a clogged sink when something is covering the drain.
In either form, when glaucoma causes pressures within the eye to rise to detrimental levels, the pressure can ultimately damage the optic nerve at the back of the eye, thereby causing vision loss, specifically a narrowing of the field of view. Treatments are available for both open-angle glaucoma (usually drugs) and angle-closure glaucoma (typically surgery), but one of the problems is early detection. Because there is no pain, patients often don't even know they have the disease until much of their field of view is already gone--and the treatments only prevent further vision loss, they don't bring it back.
Fortunately, select low vision aids can help those with vision loss due to glaucoma. Contrast-enhancing eyewear (tinted glasses) can make objects easier to see and field expanders can make objects smaller so they fit into the central part of the vision which is often still good. These devices can help those with glaucoma enhance their quality of life and allow them to maximize their independence.