We often take our eyesight for granted. But imagine what it would be like to gradually lose your vision and, by the time you notice what's happening, it's too late to reverse the damage. That's essentially what may happen when you have glaucoma and why it's so important to get regular eye exams.

Glaucoma: The "sneak thief of sight"

Glaucoma is an eye disease that affects the optic nerve and typically causes gradual visual field loss over time. Often there are no symptoms until significant visual field loss has occurred. In patients with glaucoma, typically the side or peripheral vision is lost first, characterized by a narrowing of what is seen outside of center focus. People experiencing impaired vision due to glaucoma may maintain 20/20 vision in their center focus and still be considered legally blind if significant peripheral visual field loss has occurred. They may not even notice the narrowing of their peripheral vision because it can be very gradual. That's why glaucoma is sometimes called the "sneak thief of sight." (Read more about the hidden effects of vision loss)

Although glaucoma cannot be cured, vision loss may be prevented. Early detection and lowering intraocular pressure (IOP) are the best defenses against vision loss associated with glaucoma. To find out if you have glaucoma or ocular hypertension (elevated IOP), you should schedule an appointment with an eye doctor.

What is intraocular pressure (IOP)?

Eye pressure is commonly referred to as intraocular pressure or IOP. Eye pressure exists because eyes produce a clear fluid to keep them nourished and healthy. When this clear fluid circulates throughout the eyes and normally drains through the eyes' "drainage pipes," IOP is considered to be "normal." It is healthy for eyes to have eye pressure within a certain safe range. (However, much like blood pressure, every individual has a different safe IOP level. There's no "magic number.")

In patients with elevated IOP , this fluid may not drain properly. The eyes' "drainage pipes" become backed up like a clogged drain, causing increased pressure inside the eyes. Increased eye pressure, or elevated IOP, is the only treatable risk factor for patients with open-angle glaucoma (To learn about other risk factors for glaucoma, see Risk Factors for Glaucoma).




Open-angle glaucoma

There are different types of glaucoma, including open-angle glaucoma, which is the most common. A less common type of open-angle glaucoma is normal-pressure glaucoma, also known as low-tension glaucoma. It is a type of glaucoma in which a person's IOP is considered "normal," but there is noticeable damage to the optic nerve consistent with glaucoma and visual field loss may have occurred. (To learn more about the different types of glaucoma, see Types of Glaucoma.)

Explore this section to learn more about glaucoma and how open-angle glaucoma may affect sight. Also be sure to visit the interactive ANIMATED TUTORIAL.