National Glaucoma Research

Causes of Open-Angle Glaucoma

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Primary Open-Angle Glaucoma

The eye produces a fluid called aqueous humor, which provides nutrition to the eye, and also maintains the eye in a pressurized state. The aqueous humor is continually produced and drains out of the trabecular meshwork, which is a network of cells and scaffolding material that sits in an area called the drainage angle. The angle can be thought of as the angle between the iris and the cornea. This drainage angle wraps 360 degrees around the circumference of the front part of the eye.

As we get older, the trabecular meshwork does not function as well, which affects how fluid flows out of the eye, and gradually the eye pressure can creep up over time. The elevated eye pressure damages the optic nerve cells and leads to irreversible vision loss.

In primary open-angle glaucoma, the most common type of glaucoma in the United States, the drainage angle is in an open configuration.

Variations of Open-Angle Glaucoma

Patients who have normal- or low-tension glaucoma have “normal” eye pressures, generally considered to be less than 21 mmHg. The fact that this type of glaucoma exists means that while eye pressure is a major risk factor for glaucoma, there are some patients whose optic nerves are susceptible to damage even at lower or “normal” eye pressures. The treatment is the same for patients with normal tension glaucoma as clinical trials have shown that lowering eye pressure, even when it is in the “normal” range, slows the disease.

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