Open-angle glaucoma (OAG) and closed-angle glaucoma (CAG) differ in characteristics, symptoms, and treatments.
“Glaucoma” is the medical term for a group of eye conditions that involve optic nerve damage. The optic nerve transmits visual information to the brain. As such, glaucoma can lead to changes in vision and vision loss.
This article describes what glaucoma is and the differences between OAG and CAG symptoms, diagnosis, and treatments. It also discusses which type is worse and considers the outlook for people living with glaucoma.
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
Doctors have not yet identified the cause of glaucoma, though they have found that it is
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.
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 (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
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
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.
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
Acute CAG causes a sudden loss of vision. Other signs and symptoms of CAG include:
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.
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
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
- 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 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.
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
|Eye drops||• prostaglandin analogs, such as latanoprost (Xalatan) |
• adrenergic agents, such as brimonidine (Alphagan P)
• beta-blockers, such as timolol (Timoptic)
• carbonic anhydrase inhibitor, such as dorzolamide (Cosopt)
• cholinergic agents, such as pilocarpine (Isopto, Carpine)
• rho kinase inhibitors, such as ripasudil and netarsudil
|Laser treatment||• laser trabeculoplasty |
• diode laser cyclophotocoagulation
• glaucoma drainage device
• non-penetrating glaucoma surgery
• minimally invasive glaucoma surgery
CAG requires emergency medical treatment. The
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
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.