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.
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.
What causes glaucoma?
This is a complicated question which many researchers, including those at Casey, are trying to understand. From ongoing research, we know that genetics, eye pressure and blood flow are all involved. The term "glaucoma" also encompasses a spectrum of diseases which behave differently from each other.
While high eye pressure (over 21 mm Hg) is commonly associated with glaucoma, it is not part of the definition of glaucoma. A person can develop glaucoma at normal eye pressures (13 to 20 mm Hg). For this reason, optic nerve examination is the key to diagnosis.
What are the risk factors for glaucoma?
The number of people who develop glaucoma varies with age and race. African Americans are 4 times more likely to develop glaucoma than whites, especially at younger ages. Glaucoma is also more common in Hispanics.
In addition, a family history of glaucoma and high eye pressure (over 21 mm Hg) are risk factors.
Based on this information, the American Academy of Ophthalmology considers the following groups at high risk for developing glaucoma and recommends that they should have a regular screening eye exam:
- Anyone with a family history of glaucoma
- African Americans over 40 years of age
- Everyone over 60 years of age, especially those of Hispanic background
How do I get screened for glaucoma?
Glaucoma can be diagnosed with a complete eye examination. This includes measuring vision and eye pressure and having a dilated eye examination to properly evaluate the optic nerve.
If any of these parameters are abnormal (for example, high eye pressure or a suspicious appearing optic nerve), further testing will be done.
What do I do if I have glaucoma?
Glaucoma is a chronic disease. Using your eye drops faithfully and having regular examinations to monitor the eye pressure and optic nerve are the two most important parts of glaucoma care. Once the eye pressure is controlled, it will be monitored every 3-6 months. This is essential because pressure can increase over time despite medications. Since even moderately high eye pressure rarely causes pain, you will not be able to tell if your pressure is elevated and need your doctor to check it on a regular basis.
Be prepared for regular checks of your optic nerve visual field. While we know visual fields can be hard to take, they are particularly sensitive at detecting changes if you already have an abnormal visual field. Glaucoma is not about a pressure. While we take into account a lot of parameters to pick a general target for your pressure, everyone is different and each nerve reacts differently to pressure. Treatment is a dynamic process, and we continually reassess our goals based on how the eye is responding to certain levels of pressure. If your nerve or field changes, we will adjust our treatment to lower your pressure even further.