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.

People who have higher eye pressure are at higher risk for glaucoma. But each type of glaucoma is different — and for some of them, experts are still learning about the causes.

How can eye pressure damage the optic nerve?

Research shows that higher eye pressure increases your risk for damage to the optic nerve. The pressure in your eye goes up if 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. The fluid passes through this spongy tissue as it drains 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. A green arrow shows where fluid forms, passes through the meshwork between the iris and the cornea, and then exits the eye.

Not everyone with higher eye pressure will develop glaucoma. Whether you develop glaucoma depends on the amount of pressure your optic nerve can take without being damaged. This amount is different for each person.  

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

What causes open-angle glaucoma?

In people with open-angle glaucoma, the fluid passes too slowly through the spongy tissue in the opening where the iris and cornea meet. This causes fluid to build up in your eye, which increases the pressure inside of your eye.  

Experts believe that when the pressure inside your eye gets too high, it can damage the optic nerve and cause vision loss. 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. 

What causes normal-tension glaucoma?

It’s possible for your optic nerve to get damaged and cause vision loss without high eye pressure. This is called normal-tension glaucoma or low-tension glaucoma.  

Experts don’t know why this happens, but it may be that your optic nerve is more sensitive than most people’s. In this case, even though the pressure in your eye is normal, lowering it can slow down or prevent more damage to your eye. 

What causes angle-closure glaucoma?

In angle-closure glaucoma, the opening where the iris and cornea meet gets blocked by the outer edge of the iris. When this happens, the fluid can’t drain out of your eye at all. This is a medical emergency.  

Angle-closure glaucoma can cause these sudden symptoms: 

  • Intense eye pain 

  • Upset stomach (nausea)  

  • Red eye 

  • Blurry vision 

If you have these symptoms, go to your doctor or an emergency room immediately.  

What causes congenital glaucoma?

In congenital glaucoma, babies are born with a problem in their eye that makes fluid drain more slowly than normal. The good news is that if a child with congenital glaucoma gets surgery soon after they are diagnosed, they have a high chance of developing good vision. 

Can other health problems cause glaucoma?

Yes — you can develop different types of glaucoma that are called secondary glaucomas.    

Health problems that can cause glaucoma include: 

  • Complications from medical conditions like diabetes or high blood pressure 

  • Cataract 

  • Certain eye tumors 

  • Inflammation of your eye  

  • Serious eye injuries 

  • A reaction to steroids used to treat some diseases 

Last updated: June 26, 2019