Narrow Angle Glaucoma vs. Open Angle Glaucoma

Glaucoma is a group of eye conditions that damage the optic nerve, often due to abnormally high pressure in the eye. It is one of the leading causes of blindness worldwide.

While there are several types of glaucoma, the two primary forms are narrow-angle glaucoma and open-angle glaucoma. Understanding the differences between narrow-angle glaucoma vs open-angle glaucoma is crucial for early detection, effective treatment, and prevention of vision loss.

Glaucoma is a condition that results from damage to the optic nerve. This part of the eye is responsible for transmitting visual information from the eye to the brain.

The damage to the nerve is associated with increased intraocular pressure (IOP), though glaucoma can occur even with normal IOP levels. The progression of glaucoma is typically slow and may go unnoticed until significant vision loss occurs.

Open-angle glaucoma, also known as primary open-angle glaucoma (POAG), is the most common form of the disease. Around 90% of all cases are open-angle glaucoma.

This form of the condition develops gradually. A patient’s eye drainage canals become less efficient over time, causing the condition to worsen.

There are a variety of causes for open-angle glaucoma. The most common reason patients develop open-angle glaucoma is the gradual inefficiency of the eye's drainage system. As this system becomes less effective, fluid in the eye called aqueous humor flows out. This inefficiency creates more intraocular pressure, which can damage the optic nerve over time.

Additionally, genetic predisposition plays a significant role in the development of the condition. Patients who meet the following criteria are more likely to develop open-angle glaucoma:

• Have a family history of the condition.
  

• Are over the age of 40.
  

• Have medical conditions such as high blood pressure, diabetes, and nearsightedness.

Open-angle glaucoma progresses slowly. Patients may not notice symptoms in the early stages of the condition.

As the disease progresses patients often experience blind spots and a gradual loss of peripheral vision. As the disease advances, patients may develop tunnel vision.

This slow onset makes it crucial that patients schedule regular eye exams so they can receive a diagnosis before vision loss occurs.

The most reliable way to diagnose open angle glaucoma is through a complete eye exam. During the exam a patient's eye doctor will typically:

• Measure eye pressure

• Inspect the eye's drainage angle

• Examine optic nerve for damage

• Test peripheral (side) vision

• Take a picture or computer measurement of optic nerve

• Measure the thickness of the cornea

Glaucoma damage cannot be reversed, but patients can prevent further harm through a variety of treatment methods.

Eye drops and other medications can lower eye pressure by reducing the amount of aqueous fluid the eye makes and helping the fluid flow better through the drainage angle.

Patients can also opt for surgery to treat glaucoma. For open-angle glaucoma the most common surgery is called trabeculoplasty. During the procedure a surgeon uses a laser to improve the drainage angle so fluid flows out properly and eye pressure is reduced.

Primary angle-closure glaucoma, also known as angle-closure glaucoma, acute angle closure glaucoma, and narrow-angle glaucoma, occurs when the iris is positioned too close to the drainage angle in the eye.

This can block the drainage canals suddenly (acute angle-closure) or gradually (chronic angle closure glaucoma), causing a rapid rise in intraocular pressure.

Narrow-angle glaucoma occurs due to both anatomical and physiological factors that prevent the normal drainage of aqueous humor from the eye.

Certain anatomical structures put patients at a higher risk. For instance, patients with smaller eyes, shallow anterior chambers, or thicker lenses are at a higher risk. These traits cause the iris to sit closer to the drainage angle and make blockage more likely.

Like open-angle glaucoma, genetic predisposition plays a significant role in the development of the condition. Patients who meet the following criteria are more likely to develop narrow-angle glaucoma:

• Diagnosed as farsighted: increases the risk due to anatomical structure.
  

• Are over the age of 50.
  

• Have Asian or Inuit heritage (more prevalent in these groups).

Unlike open-angle glaucoma, narrow-angle glaucoma often causes sudden, severe symptoms, especially in acute cases. These include:

• Eye pain and redness

• Severe headache

• Blurred vision

• Halos around lights

• Nausea and vomiting

If patients notice symptoms, they should contact their eye doctor for an exam. During the exam a patient's eye doctor will typically:

• Test the eye's drainage angle with a test called a Gonioscopy.

• Use a slit-lamp exam to see further inside a patient’s eyes.

• Test pressure of patient’s eyes.

• Test peripheral (side) vision.

• Evaluate optic nerve and vision loss.

Unlike open-angle glaucoma, narrow-angle glaucoma is considered a medical emergency and may require more urgent treatment. Following a diagnosis, eye doctors will typically prescribe either eye drops or oral medication to lower intraocular pressure.

Additionally a patient’s eye doctor may recommend a procedure called a laser iridotomy to prevent further optic nerve damage.

During the procedure, a surgeon creates a hole in the iris to allow fluid to flow freely. The surgeon will typically perform the operation on both eyes to prevent the risk of having an episode in a patient's other eye.

Both forms of glaucoma share several key similarities. The two conditions result in critical damage to the optic nerve. This damage, if left untreated, can lead to irreversible vision loss.

Both narrow-angle glaucoma and open-angle glaucoma can increase intraocular pressure, which is a significant risk factor in both types of glaucoma. While elevated IOP is not always present in every case, it remains a crucial indicator for assessing the risk and progression of the disease.

Though the specific procedures and medications vary, both forms of glaucoma can be treated with prescription eye drops, medication, and surgery.

While both narrow-angle and open-angle glaucoma affect the optic nerve and can lead to vision loss, there are key differences.

Open-angle glaucoma is more common, developing gradually as the eye's drainage canals become less efficient, leading to a slow increase in intraocular pressure. In contrast, narrow-angle glaucoma is less common and can develop suddenly due to the iris blocking drainage canals, causing a rapid rise in eye pressure.

Symptom onset also varies. Open-angle glaucoma is often asymptomatic early on, with gradual peripheral vision loss over time. Narrow-angle glaucoma, however, can cause sudden, severe symptoms.

Diagnosis for both involves comprehensive eye exams, but gonioscopy is crucial for narrow-angle glaucoma to assess the angle between the iris and cornea.