There are many types of glaucoma. Often, the cause of high pressure in the eye can help tell the type of glaucoma and the best treatment for it. The most common types include:
Chronic (Open Angle) Glaucoma
This is the most common type. In open angle glaucoma, aqueous fluid drains too slowly and pressure inside the eye builds up. It usually results from aging of the drainage channel, which doesn’t work as well over time. However, younger people can also get this type of glaucoma.
Normal Tension Glaucoma
This is a form of open angle glaucoma not related to high pressure. People with normal tension glaucoma may be unusually sensitive to normal levels of pressure. Reduced blood supply to the optic nerve may also play a role in normal tension glaucoma.
Acute (Angle Closure) Glaucoma
Those of Asian and Native American descent are at higher risk for this form of glaucoma. It occurs when the drainage system of the eye becomes blocked. It causes a sudden rise in pressure, requiring immediate, emergency medical care. The signs are usually serious and may include blurred vision, severe headaches, eye pain, nausea, vomiting or seeing rainbow-like halos around lights. Occasionally, the condition may be without symptoms; similar to open angle.
Secondary glaucoma is the result of another eye condition or disease, such as inflammation, trauma, or tumor.
How Does Glaucoma Damage Your Eyes?
Doctors don’t know exactly how glaucoma damages the optic nerve. For many people, increased eye pressure seems to play an important role.
Your eye produces a watery fluid (aqueous humor), which goes into the eye and drains out. When your eye is healthy, the fluid drains through a mesh-like pathway and into the bloodstream. Aqueous fluid is produced by the ciliary body. It flows through the pupil and behind the clear cornea. Finally, it drains away through the trabecular meshwork.
For some people, fluid can’t drain properly because of a faulty drainage system. Drainage that once worked well may gradually slow down as you get older. A sink that becomes clogged backs up with water. When there is no place for excess fluid to go, pressure inside the eye builds up.
This increased eye pressure may damage the optic nerve over time. Slowly, the nerve fibers that are essential for vision die.
For others, glaucoma damages the optic nerve without increased pressure. These people may be unusually sensitive even to normal levels of pressure. Their glaucoma may also be related to problems with blood flow in the eye. Doctors continue to study eye pressure and other possible causes of glaucoma.
Different people experience glaucoma differently. Usually, glaucoma affects side vision (peripheral vision) first. Late in the disease, glaucoma may cause “tunnel vision.” In this condition, the person can only see straight ahead. That’s why someone with glaucoma can have good straight ahead (central) vision. However, even central vision can be seriously damaged.
Glaucoma Risk Factors
These risk factors may increase your chance of having glaucoma:
The older you are, the greater you are at risk (especially if you are over 60 years old). African Americans are at a greater risk at a younger age starting at age 40 and older.
African-Americans age 40 and over are 4-5 times more likely to have glaucoma than others. Hispanics are also at increased risk for glaucoma as they age. Those of Asian and Native American descent are at increased risk for angle closure glaucoma.
If you have a parent, brother or sister with glaucoma, you are more likely to get glaucoma. If you have glaucoma, inform your family members to get complete eye exams.
You are at risk if you have a history of high pressure in your eyes, previous eye injury, long term steroid use, or nearsightedness.
Signs of Glaucoma
There are three major signs that a person may have glaucoma:
Your eye doctor will check your eyes using some of these tests:
The doctor will place a few drops in your eye to open or dilate the pupil. This allows the doctor a clearer view to inspect the optic nerve at the back of the eye.
Photography or Optic Nerve and Retinal Imaging
Photography or Optic Nerve and Retinal Imaging or laser scanning may be used to show the appearance of the optic nerve inside your eye. This may also involve dilating your eye.
Tonometry measures pressure in the eye. Medicine drops are used to numb the eye. An instrument gently presses on the outside of your eye. Pressure is shown as a number followed by the abbreviation “mm Hg.” This stands for “millimeters of mercury,” a standard measure for pressure. An average pressure is about 16 mm Hg. Still, a higher than average number doesn’t always mean you have glaucoma. Since the thickness of the cornea (the front window of the eye) may affect the pressure reading and the risk of glaucoma progression, your doctor may measure this as well. Pressure can also be measured by non-contact tonometry, also known as the air puff test.
Perimetry evaluates your visual field. This tests your vision all around your field of view to see if any areas are missing. It usually involves staring straight ahead at a light and trying to see lights that appear around the sides of your view. This is generally done with a computerized system.