GLAUCOMA

written by Dr. William McSwain

WHAT IS GLAUCOMA?

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.

HOW IS GLAUCOMA DIAGNOSED?

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.

WHAT IS A GLAUCOMA SUSPECT?

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.

WHAT CAN BE DONE TO TREAT GLAUCOMA?

Treatment of glaucoma is focused on early detection and treatment to protect your vision and prevent further vision loss. The only currently known way to slow down or stop the progression of glaucoma is to lower the intraocular pressure. There are many treatment regimens available that successfully prevent vision loss from glaucoma. If your glaucoma is diagnosed at an early stage and you are compliant with your treatment regimen and attend all of your appointments, your chance of ever having symptomatic vision loss from glaucoma is low. However, many patients still lose vision unnecessarily because they are non-compliant with their medications or do not follow up at all of their appointments.

First line treatment of glaucoma involves eye drops, laser trabeculoplasty, or a combination of both. There are many more eye drops available for glaucoma than there used to be and they are very effective. However, some people may not want to use eye drops because they can be expensive, may cause side effects, or may be hard to put in making compliance difficult. If you are using eye drops, it is very important you strictly adhere to the prescribed regiment. If you frequently miss doses, your eye pressure will elevate during those times causing damage to the optic nerve.

If you do not like or are having difficulty with using eye drops, then a  laser trabeculoplasty may be a good option. Laser trabeculoplasty is a very low risk and relatively painless procedure that involves treating the drainage system in the eye to improve its function and lower the intraocular pressure. It is effective in around 80% of people but may need to be repeated if it loses its effectiveness over time.

If you have angle-closure glaucoma, a laser peripheral iridotomy (LPI) is performed. This procedure involves using a laser to open a small hole in the iris (the colored portion of your eye) to provide a pathway for fluid to drain and open the drainage system. Some people may need further laser treatment or will also need to be treated with pressure lowering eye drops.

If the glaucoma becomes severe or continues to progress despite medical therapy, then surgery may be indicated. There are many different types of surgical options, each with their own advantages and disadvantages. The most common glaucoma surgeries include trabeculectomy, tube shunt, Ex-PRESS mini shunt, viscocanalostomy, canaloplasty, XEN gel stent, iStent, and ciliary body ablation.

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

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