Glaucoma is an eye disease that involves damage to the optic nerve, the part of the eye that carries the images we see to the brain. The optic nerve is like an electric cable containing about 1.2 million wires. This condition can damage nerve fibers, causing blind spots to develop. In the most common type of Glaucoma, patients may experience a gradual narrowing of their peripheral vision that creates “tunnel vision.” Glaucoma is a leading cause of blindness in the United States, especially for older people, but loss of sight can often be prevented with early treatment.
There are several different types of glaucoma, but they are all characterized by damage to the optic nerve. The most common is open-angle glaucoma, which accounts for 90% of all cases of glaucoma and is associated with elevated intraocular pressure (IOP).
Along with closed-angle glaucoma, this is one of the two main types of glaucoma. The term “open-angle” means the angle where the iris meets the cornea is open and normal. This type of glaucoma is also called primary open-angle glaucoma. In open-angle glaucoma, elevated IOP can result in damage to the optic nerve. However, many patients with open angle glaucoma never experience an increase in IOP, suggesting that blood flow or other genetic factors may be responsible. Open-angle glaucoma develops slowly and is a lifelong condition. Although it cannot be cured, early diagnosis can provide an excellent opportunity to prevent further vision loss.
Narrow-angle glaucoma, which is also called closed-angle glaucoma or angle-closure glaucoma, is most common in people of Asian heritage and people who are farsighted. With this type of glaucoma, the angle between the iris and the cornea is narrower than normal, making it difficult for the eye’s fluid to drain, and causing increased pressure within the eye. Sometimes, this increased pressure occurs in extreme spikes.
With closed-angle glaucoma, the reduced space for fluid to flow through becomes compromised, blocking the eye’s drainage canals. This can develop very quickly and result in a sudden increase in eye pressure. When an acute attack of closed-angle glaucoma occurs, it is a medical emergency requiring immediate medical treatment.
Also called low-tension or normal-pressure glaucoma, normal-tension glaucoma is characterized by optic nerve damage that appears to be pressure-related even though it is not accompanied by high eye pressure. No one knows why this occurs, but researchers think it may be related to poor blood flow to the optic nerve. Risk factors for normal tension glaucoma include people with a family history of the disease, those of Japanese descent, and those with a history of systemic heart disease
Because normal-tension glaucoma, by definition, is not accompanied by high eye pressure, it must be diagnosed by looking for signs of damage to the optic nerve and by checking for peripheral vision loss. Your doctor can scan your eye with optical coherence tomography (OCT) to evaluate the condition of the optic nerve, and perform an ophthalmoscopy, a test that lets the doctor see inside the eye to observe the optic nerve. An optic nerve that’s cupped or not a healthy pink color is a sign of trouble. A visual field test will show the doctor any sight loss that may not be apparent to the patient.
Because the optic nerves of patients with normal-tension glaucoma can be damaged at relatively low levels of IOP the condition is frequently treated the same way as “regular” open-angle glaucoma, by lowering IOP with medications and surgery.
