Catching the disease early is key for preserving your vision.

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Glaucoma is a serious eye condition that can lead to loss of sight and even blindness, if it progresses far enough. Most types of glaucoma are asymptomatic in early stages—meaning you might not even notice something's off with your vision until the damage has already been done.

Some types of glaucoma, however, do have noticeable symptoms early on. Knowing the signs that might pop up—and getting screened for glaucoma during your routine eye exam—will help you catch the disease early on, so that you can get the treatment you need.

What is glaucoma?

According to the National Eye Institute (NEI), glaucoma is a group of eye diseases that causes damage to the optic nerve—the nerve in the back of the eyes that allows them to communicate with your brain. Damage to this essential nerve causes vision loss, and ultimately, if it becomes very damaged, blindness.

The causes aren't totally clear, but many people with glaucoma have high eye pressure, called intraocular pressure, or IOP. Treatments that lower eye pressure, like prescription eye drops and surgeries that either open up the existing drainage area in the eye or add stents to improve drainage, help slow down or stop the nerve damage. As of now, doctors aren't totally sure what causes the disease to start, though age and genetics are two of the biggest risk factors.

"Glaucoma is one of the most common causes of vision loss and blindness in the world," Christopher Starr, MD, ophthalmologist at Weill Cornell Medicine and NewYork-Presbyterian Hospital, tells Health. "One of the problems with glaucoma is it's often asymptomatic." It's usually not until the optic nerve has been significantly damaged that people will notice symptoms of glaucoma. Doctors still don't have a way to repair optic nerve damage, so if glaucoma goes unchecked for too long, it can have permanent consequences.

That's why it's so important to get screened regularly for glaucoma, says Sriranjani Padmanabhan, MD, ophthalmologist and glaucoma specialist at UCSF Health. "The only reliable way to detect it is to have an eye exam," she tells Health. In the US, eye pressure is measured during a routine eye exam. If your eye pressure is high, or if you have any other risk factors that put you at a higher risk for glaucoma, your doctor may perform additional tests to determine whether you need treatment.

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Though glaucoma is usually asymptomatic, you may notice some signs of the disease, depending on which type of glaucoma you have. Here's what to keep an eye out for (pun intended).

Open-angle glaucoma symptoms

Open-angle glaucoma is the most common form of glaucoma, Dr. Starr says. It happens when the drain in the eye is compromised in some way and not draining fluid properly, resulting in a build-up of pressure.

This type of glaucoma usually progresses very slowly and is asymptomatic until vision loss occurs in its later stages. The first symptom is usually loss of peripheral (side) vision, Dr. Starr says—which can be tough to notice. "Peripheral vision is much harder for people to identify problems with. If you have blockage of your central vision, that's pretty obvious pretty quickly. But most of us are just not that aware of peripheral vision or the extent of it," he says.

Since vision damage from glaucoma happens slowly over time and usually in one eye quicker than the other, people often compensate for and adjust to small changes without noticing. It's not until it's really bad that a person can see it. Some people may have peripheral vision loss from glaucoma and not even realize it until they see an eye doctor, Dr. Starr says.

"You may feel like you are looking through a tunnel," Dr. Padmanabhan says. "Sometimes if you close one eye, you'll notice a difference in vision in one versus the other." But generally, it's hard to notice these changes until vision damage is significant.

Normal-tension glaucoma symptoms

About 1 in 3 people with open-angle glaucoma have what's known as normal-tension glaucoma, a type of glaucoma that happens when the eye pressure level is considered normal, according to the NEI.

"The pressure is not technically elevated, but the optic nerve is sensitive to the normal pressure in the eye and can still be damaged," Dr. Starr explains. "Typically, this is only detected on eye exams where nerve damage is seen." Like open-angle glaucoma in general, this type of glaucoma is rarely symptomatic, but when it becomes advanced, you will notice changes in your vision, starting with loss of peripheral vision.

Angle-closure glaucoma symptoms

Angle-closure glaucoma happens when the iris of the eye is not as open as it should be, usually because the distance between the iris and lens is narrow. This usually happens as you age, and the lens of the eye gets larger. In someone with a narrow angle of the eye, when the pupil enlarges and narrows, it can bunch up and blocks the drainage canals, according to the Glaucoma Research Foundation.

This can happen really suddenly and cause a very quick and dramatic increase in eye pressure, known as acute angle-closure glaucoma. Because it happens so quickly, symptoms of acute angle-closure glaucoma are very noticeable, and damage occurs quickly, too. It's rare, but when it happens, it's a medical emergency.

"A person would know it's happening," Dr. Starr says. Symptoms include redness of the eye, blurred vision, halos around lights, severe eye and head pain, and nausea and vomiting. "That's a true medical emergency and you need to seek out care." 

Angle-closure glaucoma can also happen slowly over time, similarly, to open-angle glaucoma, according to Merck Manual. This is called chronic angle-closure glaucoma and is often asymptomatic until significant damage to the optic nerve and ensuing vision loss occurs.

Congenital or childhood glaucoma symptoms

About 1 out of 10,000 babies born in the US are born with a defect in the eye that prevents fluid from draining normally, according to the NEI. This is called congenital glaucoma, and usually, you can notice the symptoms soon after the baby is born. Symptoms include cloudy eyes, light sensitivity, extra tear production, and sometimes, eyes that are larger than normal. If surgery is done early enough, vision can usually be preserved.

Children can also develop glaucoma, but this is now pretty rare in the US, Dr. Padmanabhan says.

Secondary glaucoma symptoms

Secondary glaucoma is used to explain when glaucoma happens as a result of another condition. There are four main types—some of which may be more symptomatic than others.

  • Neovascular glaucoma happens when extra blood vessels form in the eye and cover the drainage areas. It's usually caused by a medical condition, including diabetes and high blood pressure. Neovascular glaucoma may cause pain and redness of the eye, and eventually, vision loss.
  • Pigmentary glaucoma, also known as pigment-dispersion syndrome, happens when pieces of pigment from the iris come loose and block the eye's drainage system. Symptoms of pigmentary glaucoma can include blurry vision and rainbow-colored halos around lights, and can be stimulated by exercise, Dr. Starr says. "Doing strenuous exercise might liberate some of those pigment cells, and so people will have characteristic symptoms of eye pain and/or blurry or foggy vision after strenuous exercise."
  • Exfoliation glaucoma, also called pseudoexfoliation, is another type of open-angle glaucoma that's caused by exfoliation syndrome. Exfoliation syndrome is a condition that causes tissue from different parts of the eye to detach, which can block the eye's drainage systems similarly to pigmentary glaucoma. It often progresses quicker than other types of open-angle glaucoma, so you may notice problems with your vision earlier on—but this also means it can also damage the eye quicker.
  • Uveitic glaucoma is caused by uveitis, a condition that causes inflammation in the eye. Experts think that the inflammation itself and the scar tissue that forms in the eye somehow damages or blocks the drainage system in the eye, causing high pressure. Corticosteroids used to treat uveitis may also cause high intraocular pressure.

In the majority of cases, people with glaucoma won't feel anything and may not notice vision changes until the disease has progressed pretty far, Dr. Padmanabhan says. Which is why having regular screening and early diagnosis is so critical—identifying who is at a higher risk of glaucoma and treating glaucoma ASAP is the best way to prevent any additional optic nerve damage and preserve long-term vision.

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