written by Dr. William McSwain

Glaucoma is a disease of the optic nerve, the nerve that connects the eye to the brain. There are around one million individual nerve fibers in the optic nerve. Each nerve fiber corresponds to a small point in your visual field, just like pixels on a TV screen. In glaucoma, these nerve fibers are progressively becoming damaged and dying off. When an optic nerve fiber dies, you lose that corresponding area of your vision permanently.

There are two main forms of glaucoma: open-angle glaucoma and angle-closure glaucoma. Some people may have components of both open-angle and angle-closure glaucoma. Both forms involve disruption of the drainage system which drains fluid from inside the eye leading to elevated pressure and damage to the optic nerve.

In angle-closure glaucoma, the area around the eye’s drainage system may be narrow or blocked. If the drainage system is blocked, fluid cannot escape and pressure builds up which can damage the optic nerve. Angle-closure glaucoma tends to progress more quickly than open-angle glaucoma. It can occur suddenly as in acute angle-closure glaucoma which is an emergency and needs to be treated immediately. Angle-closure glaucoma can occur in anyone but is more common in the elderly, women, hyperopes (people who are farsighted), and people of African or Asian descent.

In open-angle glaucoma, the area around the eye’s drainage system is clear but the drainage system itself is not functioning properly causing pressure to build up in the eye. Open-angle glaucoma is more common than angle-closure glaucoma and tends to progress more slowly, even taking years to decades to develop. Both forms of glaucoma tend to progress more rapidly the older you get.

Glaucoma can be difficult to diagnose. It is usually painless and most patients do not notice any symptoms of their vision loss until it becomes severe. Vision loss tends to progress slowly and usually only affects the peripheral vision until late stages in the disease. This may make identifying people who have early or moderate glaucoma difficult because many are not yet at a stage where they have developed symptoms that cause them to make an appointment with their ophthalmologist. It is estimated that nearly half of the people who have glaucoma are undiagnosed. Many times, glaucoma is detected on routine screening or when a patient presents to their ophthalmologist for a different problem.

The diagnosis of glaucoma involves a combination of the patient history, physical exam, and testing involving visual fields, ERG, and high definition imaging of the optic nerves. If you are diagnosed with glaucoma, these tests will need to be repeated at regular intervals the rest of your life to determine if the glaucoma is stable and the treatment is working. If testing shows the glaucoma is progressing, then more aggressive treatment to lower the intraocular pressure (the pressure inside the eye) is needed.

Because glaucoma tends to run in families, if you are diagnosed you should contact any first-degree relatives (father, mother, siblings, children) and recommend they make an appointment for a glaucoma evaluation.

Some people have a history and exam that is concerning for glaucoma, but their initial testing is normal. These people are referred to as glaucoma suspects. Glaucoma suspects have optic nerves that appear suspicious for glaucoma and may have very early glaucoma that is not yet showing up on testing. Because vision loss that occurs with glaucoma is irreversible, it is in your best interest if the glaucoma is identified and treated as early as possible. Glaucoma suspects are usually followed every six months so that if the glaucoma progresses and begins to cause vision loss, it can be diagnosed and treated as early as possible before it becomes symptomatic.

ADDITIONAL READING:  https://nei.nih.gov/health/glaucoma