Ophthalmologists explain the different types of glaucoma that can affect eye health.

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The health of your eyes is not something to take lightly—and yet, for the most part, we don't normally pay close attention to our eye health until something is wrong. And with glaucoma specifically, once you notice symptoms, it usually means a significant amount of damage has already occurred.

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Generally speaking, glaucoma isn't just one condition—it's actually a group of eye disorders that causes damage to the optic nerve, Sriranjani Padmanabhan, MD, ophthalmologist and glaucoma specialist at UCSF Health, tells Health. That optic nerve is the nerve in the back of the eye that allows it to communicate with your brain so that you can see. Damage to the nerve is irreversible and over time, causes vision loss and eventually, if it goes unchecked, blindness—that's why your best defense against glaucoma is to catch it soon through regular eye exams, says Dr. Padmanabhan.

Luckily, when it is caught early, glaucoma can be treated through a combination of eye drops, laser treatments, and surgeries. But your specific treatment regimen for glaucoma depends on a few different factors, including which specific type of glaucoma you have. And while all types of glaucoma have one very important thing in common (damage to the optic nerve), there are some pretty important differences between them, as well. Here, eye doctors explain the five different types of glaucoma, and how they affect eye health.

Open-angle glaucoma

Open-angle glaucoma is the most common form of glaucoma, affecting 3 million Americans, according to the Glaucoma Research Foundation (GRF). The "open-angle" part of open-angle glaucoma simply means that the angle where the iris meets the cornea is as open as it should be, per the GRF.

Causes: The vast majority of people with glaucoma also have high levels of pressure within the eye. This pressure is known as intraocular pressure (IOP). In a healthy eye, old fluid is drained, and new fluid is produced at a steady rate; but in those with open-angle glaucoma, the eye's drainage system isn't draining properly, causing fluid buildup in the eye. Over time, this can put undue pressure on the optic nerve. "Pressure on the optic nerve causes the fibers to slowly die," Christopher Starr, MD, ophthalmologist at Weill Cornell Medicine and NewYork-Presbyterian Hospital, tells Health.

Symptoms: This type of glaucoma progresses slowly and is often asymptomatic until the optic nerve has been damaged enough to cause vision loss. Loss of peripheral (side) vision, or feeling like you're looking through a tunnel, is usually the first noticeable symptom, Dr. Padmanabhan says. 

Angle-closure glaucoma

Angle-closure glaucoma is less common than open-angle glaucoma, but it can lead to an "attack" that causes a rapid, dangerous, and often painful increase in eye pressure, per the GRF. It can be chronic and go unnoticed, similarly to open-angle glaucoma, if it never leads to an attack.

Causes: With angle-closure glaucoma, the angle between the iris and cornea is either too narrow or completely closed off, blocking fluid from draining out of the eye. A narrow angle can be caused by past injury or surgery and scarring, advanced cataracts, tumors, or even extreme far-sightedness, Dr. Starr says. But most commonly, genetics predisposes someone to angle-closure glaucoma and eventually, the angle becomes completely blocked, causing a rapid increase in eye pressure, Dr. Starr explains.

Symptoms: Angle-closure glaucoma can happen acutely—meaning it's sudden and causes a quick and dramatic increase in eye pressure. Symptoms are usually quite noticeable, Dr. Starr says. "A person would know it's happening." Redness of the eye, blurred vision, halos around light, severe eye and head pain, and even nausea and vomiting from the pain, can be signs of acute angle-closure glaucoma. This requires immediate medical attention to fix the problem and lower pressure before the optic nerve is damaged.

Normal-tension glaucoma

Normal-tension glaucoma is a type of open-angle glaucoma where the eye pressure reads normal, but the optic nerve is sensitive to the pressure for some reason. About 1 in 3 people with open-angle glaucoma have normal-tension glaucoma, according to the National Eye Institute (NEI).

Causes: Normal-tension glaucoma is still somewhat of a mystery. Experts aren't sure why, but some people's optic nerves just seem to be sensitive to pressure levels within "normal" range. "The pressure is normal, it looks like the drain is working, but for whatever reason, the pressure is still not low enough," Dr. Padmanabhan says.

Symptoms: Normal-tension glaucoma is usually asymptomatic until the optic nerve has been damaged and there is some amount of vision loss. Changes in peripheral vision are typically the first noticeable sign.

Congenital glaucoma

Congenital glaucoma is rare, affecting about 1 out of 10,000 babies born in the US, according to the NEI. It's usually diagnosed within the first year of life, according to the GRF, though some people may not be diagnosed until they are a few years old. If surgery is done soon after it's discovered, the glaucoma can often be corrected, and eyesight is preserved. Some people may require additional medications (like eye drops) or surgeries.

Causes: Congenital glaucoma is caused by incorrect or incomplete development of the eye's drainage canals while a baby is developing in the womb, per the GRF.

Symptoms: Congenital glaucoma usually has noticeable symptoms, including cloudy eyes, light sensitivity, extra tear production, and sometimes, eyes that are larger than normal.

Secondary glaucomas

Some medical conditions can cause glaucoma. When this happens, the glaucoma is called secondary glaucoma.

Causes: Various injuries and conditions can cause secondary glaucoma. Eye trauma and surgeries can cause scarring in the eye, leading to secondary glaucoma. Certain medical conditions, like diabetes and high blood pressure, can cause blood vessels to develop in the eye and cover drainage areas—known as neovascular glaucoma. A condition known as exfoliation syndrome can cause tissues in the eye to detach and block the drainage system, causing exfoliation glaucoma. Pigment-dispersion syndrome, which happens when pieces of pigment from the iris break loose and block the eye drainage system, can also cause glaucoma. Uveitis, a condition that causes inflammation in the eye, may lead to scar tissue formation and block the eye's drainage canals. Certain medications can also cause an increase in eye pressure—corticosteroids are the most notorious example.

Symptoms: Some types of secondary glaucoma cause noticeable symptoms, like eye pain, redness, blurry vision, and halos around lights. Others may be asymptomatic and only apparent if an eye exam detects high pressure.

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