Updated by Sefy Paulose, March, 2022

Explanation of Glaucoma

Glaucoma is a group of eye diseases that can lead to blindness by damaging the optic nerve. The eye continuously produces a fluid, called the aqueous humor, that must drain from the eye through the eye’s drainage system, or angle, to maintain a healthy eye pressure. The different types of glaucoma are described by whether this drainage system is open or narrow. One cause of increased eye pressure is when the drainage system, or angle, is narrow or blocked.

Primary Open Angle Glaucoma

In the United States, the most common type of glaucoma is Primary Open Angle Glaucoma (POAG). In POAG, the eye’s drainage system appears to be normal or open, yet the eye has high pressure. This is thought to be due to increase production of the fluid in the eye, or aqueous humor. If the fluid in your eye can’t drain fast enough, it creates pressure that pushes on the optic nerve in the back of your eye.  Over time, the pressure damages the optic nerve, which affects your vision. People often do not have symptoms until they start to lose their vision, and people may not notice vision loss right away. (Types of Glaucoma | National Eye Institute (nih.gov))

Open angle glaucoma is termed “primary” if there are no other underlying factors that could cause the elevated pressure. If there is an identifiable cause for an increased eye pressure, the condition is called Secondary Open Angle Glaucoma (see below).

POAG is treated by decreasing the production or by increasing the drainage of aqueous humor. This can be achieved with medications (eye drops or pills), specific kinds of laser treatments or by surgery.

Primary Angle Closure Glaucoma

Primary Angle Closure Glaucoma is much less common than POAG in the United States. In this type of glaucoma, the aqueous humor cannot drain properly because the entrance to the drainage canal is either too narrow or is closed completely. In this case, eye pressure can episodically especially when triggered by pupil dilation, which happens intermittently throughout the day with changes in light. If the angle is narrow but not completely closed, symptoms can be vague such as pain, headaches and blurry vision. Symptoms of sudden angle-closure glaucoma can include sudden eye pain, nausea, headaches, and blurred vision. If you experience these symptoms, you should seek immediate medical treatment.

Normal Tension Glaucoma

In this type of glaucoma, also called low-pressure glaucoma, the drainage system of the eye appears normal, and the eye pressure is not elevated. Yet, there is still evidence of optic nerve damage. This type of glaucoma is treated much like POAG, but the eye pressure needs to be kept even lower to prevent progression of vision loss.

According to the NEI, “You may be at higher risk for normal-tension glaucoma if you:

  • Are of Japanese ancestry
  • Have a family history of normal-tension glaucoma
  • Have had certain heart problems, like an irregular heartbeat
  • Have low blood pressure”

Secondary Glaucomas

Secondary glaucomas are those that develop as secondary to, or as complications of, other conditions such as eye trauma, cataracts, diabetes, eye surgery, inflammation, or tumors.

Treatment of these would include treating the underlying cause of the glaucoma as well as eye-pressure lowering medication as above. As in the other types of glaucoma, the sooner eye pressure is normalized, the more functional vision can be preserved.

Series of four photos demonstrating typical progression of vision loss due to glaucoma. Source: National Eye Institute


The typical progression of vision loss from glaucoma
Source: National Eye Institute

Additional Information

Types of Glaucoma | National Eye Institute (nih.gov)

Patient’s Guide to Living with Glaucoma and Guía del Paciente: Vivir con Glaucoma