Glaucoma is a group of eye diseases that can cause vision loss and blindness by damaging the nerve in the back of your eye called the optic nerve.

Experts aren’t sure what causes the most common types of glaucoma, but people who have high eye pressure are at higher risk for glaucoma. Your eye doctor can check for glaucoma during a comprehensive dilated eye exam.

What does eye pressure have to do with glaucoma?

Research shows that high eye pressure increases your risk for glaucoma. Experts believe that when the pressure inside your eye gets too high, it can damage the optic nerve and cause vision loss. And studies show that lowering eye pressure can help stop vision loss from glaucoma. That’s why it’s important to control the pressure inside your eyes.

But not everyone with high eye pressure will develop glaucoma — and some people with normal eye pressure get glaucoma. Whether you develop glaucoma depends on the amount of pressure your optic nerve can handle — and this amount is different for each person. For most people, eye pressure above 21 is higher than normal.

Getting regular dilated eye exams can help your eye doctor figure out what level of eye pressure is normal for you.

What happens when you have high eye pressure?

The pressure in your eye gets higher when fluid can’t drain normally out of the front of your eye.  

Between the cornea (clear front layer of the eye) and the iris (colored part of the eye), there’s a space called the anterior chamber. Fluid normally flows through this space and out of an opening where the iris and cornea meet. The opening has spongy tissue in it, called the trabecular meshwork. The fluid passes through the meshwork to drain out of the eye.  

The green arrow in the diagram below shows how the fluid normally moves through the eye.

A diagram of the eye with a green arrow showing how fluid normally passes through the space between the iris and the cornea and drains out of the eye back into the bloodstream.

In some common types of glaucoma, fluid can’t move normally through the eye:

  • In open-angle glaucoma, the fluid passes too slowly through the spongy tissue in the opening where the iris and cornea meet
  • In angle-closure glaucoma, the opening gets blocked completely by the outer edge of the iris

In both cases, fluid builds up and increases the pressure inside the eye.  

Last updated: September 13, 2021