Open- vs. closed-angle glaucoma: What is the difference?

Share on Pinterest

Glaucoma is a group of eye conditions that cause damage to the optic nerve. This nerve is critical for vision.

Cells called retinal ganglion cells (RGCs) have axons that extend along the optic nerve. These cells transmit visual information from the eye to the brain.

Glaucoma involves a loss of RGCs and axons within the optic nerve, resulting in progressive loss of peripheral vision. Over time, vision loss may progress further and affect a person’s central vision.

Doctors have not yet identified the cause of glaucoma, though they have found that it is associated with increased pressure inside the eye. Doctors may refer to this as elevated intraocular pressure (IOP).

Eye pressure explained

The front part of the eye contains a clear liquid called aqueous humor that helps nourish the eye. The eye continually produces a small amount of aqueous humor.

Aqueous humor flows out into a spongy structure at the front of the eye called the trabecular meshwork, a part of the drainage angle. The drainage angle is the part of the eye where the iris meets the cornea.

In a healthy eye, there is a balance between the amount of aqueous humor the eye produces and the amount of aqueous humor it drains. This results in healthy eye pressure.

In some cases, aqueous humor cannot effectively drain from the eye, resulting in elevated IOP. Some factors that can affect drainage include:

• structural differences in the eye, such as having a shallower drainage angle
• closure of the drainage angle
• blockage of the drainage angle

Glaucoma may be primary or secondary.

Doctors use the term “primary glaucoma” to refer to glaucoma with no identifiable cause. The term “secondary glaucoma” refers to glaucoma due to an underlying health condition.

Medical professionals have categorized glaucoma into different types, including OAG and CAG.

Open-angle glaucoma

The most common type of glaucoma is primary open-angle glaucoma (OAG). With this type, the drainage angle formed by the iris and cornea remains open. OAG causes progressive damage to the optic nerve.

Medical professionals have not yet identified the cause of OAG. The American Optometric Association notes it may occur due to inefficient aqueous humor drainage, or as a result of inadequate blood supply to the optic nerve.

OAG is generally a painless condition that typically affects vision in both eyes. People with this condition may lose a significant portion of their vision before they notice any vision loss.

Closed-angle glaucoma

Closed-angle glaucoma (CAG) occurs when the drainage angle formed by the iris and the cornea closes or becomes obstructed.

CAG is a medical emergency. It is less common than OAG.

CAG typically affects only one eye. However, the unaffected eye has a 40–80% chance of developing acute CAG within 5–10 years of the initial incident.

In most cases, drainage angle blockages are due to the structural anatomy of the eye. Specifically, they are more likely to occur if there is a shallower angle between the iris and the cornea.

CAG is worse because people can lose their vision within 1 day of developing symptoms.

While CAG is worse, it is rare. OAG affects more people. Experts suggest that by 2040, around 111.8 million people worldwide will have OAG.

People with OAG may not experience any symptoms, especially during the earlier stages of the disease.

Collecting a thorough medical and family history can help doctors diagnose glaucoma or identify people at risk of developing the disease.

In addition, eye exams can measure eye pressure, a risk factor for OAG.

Open-angle glaucoma

Changes in vision may be the first symptom of OAG. Vision loss with OAG starts with loss of peripheral vision. People may only notice tunnel vision once they have sustained permanent damage to around 40% of their optic nerves.

Closed-angle glaucoma

Acute CAG causes a sudden loss of vision. Other signs and symptoms of CAG include:

• corneal edema, which is swelling of the cornea
• eye pain in one eye
• headache with blurred vision
• seeing rainbow-colored halos around bright lights
• nausea
• vomiting

According to the Glaucoma Research Foundation, an eye doctor may perform a procedure called a gonioscopy to assess the internal drainage system of the eye.

Gonioscopy involves using a special lens to measure the drainage angle. It is a quick and painless test. It can diagnose glaucoma and determine whether the glaucoma is open-angle or closed-angle.

Open-angle glaucoma

Some diagnostic tests an eye doctor may perform to help diagnose and monitor OAG include:

• Visual field test: This test helps detect peripheral vision loss.
• Eye pressure test: Eye doctors may measure eye pressure using a device that expels a puff of air onto the eyeball or that makes direct contact with the eyeball. Both tests apply a small amount of pressure to the eye, allowing the eye doctor to take IOP readings.
• Exclusion: Before diagnosing OAG, an eye doctor must rule out other possible types of glaucoma. They must also rule out other conditions that can produce similar symptoms. Examples include:
  • other diseases of the optic nerve
  • retinal disorders
  • central nervous system disorders

Acute closed-angle glaucoma

Doctors may also measure eye pressure in people with acute CAG. This condition usually only affects one eye. However, testing the unaffected eye may reveal features that could increase the risk of CAG in that eye.

It is highly recommended to get regular eye exams to detect any eye conditions as early as possible. Once OAG symptoms are present, there is already irreversible damage to the eye.

People should consult an eye doctor if they develop any concerning eye symptoms or have an increased risk of developing OAG.

Risk factors for OAG include:

• being African-American, Afro-Caribbean, or West African
• being over age 40 years if African-American or over age 65 years if white
• having a family history of glaucoma
• having low blood pressure
• having type 2 diabetes

The Centers for Disease Control and Prevention (CDC) recommends people undergo a comprehensive dilated eye exam by age 40 even if they are not at risk of developing glaucoma.

The CDC states that screening among this age group can help detect glaucoma and other eye diseases in their early stages.

Below are some potential treatment options for OAG and CAG.

Open-angle glaucoma

There is currently no cure for OAG. However, treatments can help slow the progression of damage to the optic nerve and help preserve vision.

Before prescribing treatments, eye doctors set a target IOP for the affected eye.

The treatment type depends on several factors, such as the:

• type of glaucoma
• person’s medical history
• severity of the condition

The following table summarizes the different treatment options for OAG:

Closed-angle glaucoma

CAG requires emergency medical treatment. The objective is to lower pressure inside the eye.

Treatment may involve one or more of the following:

• blocking the production of aqueous humor using intravenous (IV) acetazolamide
• increasing the drainage of aqueous humor using pilocarpine eye drops
• lowering the volume of aqueous humor using intravenous mannitol

A procedure called peripheral iridectomy can cure CAG. This procedure involves using a laser to create a tiny hole in the iris so aqueous humor can escape.

Cataract surgery is another treatment option to prevent and treat CAG.

According to the CDC, glaucoma affects around 3 million people in the United States and is the second leading cause of blindness worldwide.

Glaucoma can cause visual impairment or vision loss, which can have significant effects on a person’s quality of life. It may also increase the risk of mental health conditions, such as anxiety and depression.

Early screening is key to detecting and slowing the progression of glaucoma. This, in turn, can help prevent or delay vision loss.

There are two main types of glaucoma: open-angle glaucoma (OAG) and closed-angle glaucoma (CAG).

In OAG, the drainage angle in the eye remains open. In CAG, the drainage angle is closed or blocked.

OAG is a progressive disease. CAG occurs suddenly and is a medical emergency.

OAG and CAG have different characteristics, symptoms, and treatments. While CAG is worse because of the immediate consequences, OAG affects more people.

Glaucoma screening before age 40 can help detect the disease in its early stages. Early screening is key to slowing the progression of glaucoma and helping prevent or delay vision loss.