Open-angle glaucoma is the most common type of glaucoma. Glaucoma is a disease that damages your optic nerve and can result in reduced vision and even blindness.

Glaucoma affects more than 70 million people worldwide. It’s the leading cause of irreversible blindness.

Closed-angle (or angle-closure) glaucoma makes up less than 20 percent of glaucoma cases in the United States. It’s usually more severe than open-angle glaucoma.

Both conditions involve changes in the eye that prevent proper drainage of fluid. This leads to a buildup of pressure inside the eye, which progressively damages your optic nerve.

Glaucoma can’t be cured. But with early diagnosis and treatment, most cases of glaucoma can be managed to prevent the disease from progressing to vision damage.

Glaucoma often shows no symptoms before it has caused damage to your vision. That’s one reason it’s important to have regular eye exams that screen for glaucoma.

The front part of your eye, between the cornea and the lens, is filled with a watery fluid called the aqueous humor. The aqueous humor:

  • maintains the spherical shape of the eye
  • nourishes the eye’s internal structures

New aqueous humor is constantly being produced and then drained out of the eye. To maintain proper pressure inside the eye, the amount produced and the amount drained out must be kept in balance.

Glaucoma involves damage to the structures that allow the aqueous humor to drain out. There are two outlets for the aqueous humor to drain:

  • the trabecular meshwork
  • the uveoscleral outflow

Both structures are near the front of the eye, behind the cornea.

The difference between open-angle and closed-angle glaucoma depends on which of these two drainage pathways is damaged.

In open-angle glaucoma, the trabecular meshwork offers increased resistance to fluid outflow. This causes the pressure to build up inside your eye.

In closed-angle glaucoma, both the uveoscleral drain and the trabecular meshwork become blocked. Typically, this is caused by a damaged iris (colored part of the eye) blocking the outlet.

Blockage of either of these outlets leads to an increase in pressure inside your eye. The fluid pressure inside your eye is known as intraocular pressure (IOP).

Differences in angle

The angle in the glaucoma type refers to the angle that the iris makes with the cornea.

In open-angle glaucoma, the iris is in the right position, and the uveoscleral drainage canals are clear. But the trabecular meshwork isn’t draining properly.

In closed-angle glaucoma, the iris is squeezed against the cornea, blocking the uveoscleral drains and the trabecular meshwork.

Glaucoma in the early stages usually doesn’t produce any symptoms. Damage to your vision can occur before you’re aware of it. When symptoms appear, they can include:

  • reduced vision and loss of peripheral vision
  • swollen or bulging cornea
  • pupil dilation to a medium size that doesn’t change with increasing or decreasing light
  • redness in the white of the eye
  • nausea

These symptoms primarily appear in acute cases of closed-angle glaucoma but can also appear in open-angle glaucoma. Remember, absence of symptoms isn’t proof that you don’t have glaucoma.

Glaucoma occurs when blockage of the drainage outlets for the aqueous humor causes pressure in the eye to build up. The higher fluid pressure can damage the optic nerve. This is where the part of the nerve called the retinal ganglion enters the back of your eye.

It’s not clearly understood why some people get glaucoma and others don’t. Some genetic factors have been identified, but these account for less than 10 percent of all glaucoma cases.

Glaucoma can also be caused by trauma to the eye. This is called secondary glaucoma.

Risk factors

Open-angle glaucoma represents more than 80 percent of glaucoma cases in the United States. Risk factors include:

  • older age (one study showed that open-angle glaucoma affects 10 percent of those older than 75 and 2 percent of those older than 40)
  • family history of glaucoma
  • African ancestry
  • nearsightedness
  • high IOP
  • low blood pressure (but raising blood pressure carries other dangers)
  • use of topical corticosteroids
  • inflammation
  • tumor

A high IOP can accompany glaucoma, but it’s not a sure sign. In fact, 25 to 50 percent of people with glaucoma have normal IOP.

To determine if you have glaucoma, you need a comprehensive eye exam with your eyes dilated. Some of the tests your doctor will use are:

  • Visual acuity test with an eye chart.
  • Visual field test to check your peripheral vision. This can help confirm the diagnosis, but as many as 30 to 50 percent of cells in the retinal ganglion cells may be lost before the loss shows up in a visual field test.
  • Dilated eye exam. This may be the most important test. Drops are used to dilate (open up) your pupils to allow your doctor to see into the retina and optic nerve at the back of the eye. They’ll use a specialized instrument called an ophthalmoscope. The procedure is painless, but you may have blurred close-up vision and sensitivity to bright light for a few hours.
  • Tonometry.The doctor will apply numbing drops to your eye and use a special machine to measure the pressure next to the cornea. This is painless except for a very slight sting when the drops are applied.
  • Pachymetry. After the doctor applies numbing drops to your eye, they’ll use an ultrasonic wave instrument to measure the thickness of your cornea.

Other newer techniques can help to objectively confirm the amount of loss to the optic nerve fiber. These include:

  • confocal scanning laser ophthalmoscopy
  • scanning laser polarimetry
  • optical coherence tomography

Reducing the fluid pressure inside your eye is the only proven method for treating glaucoma. Treatment usually begins with drops, known as hypotensive drops, to help reduce the pressure.

Your doctor will use your earlier pressure levels (if available) to determine a target pressure to best treat your glaucoma. Generally, they’ll aim for a 20 to 50 percent reduction in pressure as a first target. The target will be lowered if your vision continues to worsen or if your doctor sees changes in the optic nerve.

The first-line of pressure-lowering drugs are prostaglandin analogs. Prostaglandins are fatty acids found in almost every tissue. They act to improve flow of blood and bodily fluids and improve drainage of aqueous humor through the uveoscleral outlet. These are taken once at night.

Prostaglandins have few side effects, but they can cause:

  • elongation and darkening of eyelashes
  • red or bloodshot eyes
  • loss of fat around the eyes (periorbital fat)
  • darkening of the iris or the skin around the eye

Drugs used as a second line of defense include:

  • carbonic anhydrase inhibitors
  • beta-blockers
  • alpha agonists
  • cholinergic agonists

Other treatments

  • Selective laser trabeculoplasty (SLT). This is an office procedure in which a laser is aimed at the trabecular meshwork to improve the drainage and lower eye pressure. On average, it can lower pressure by 20 to 30 percent. It’s successful in about 80 percent of people. The effect lasts from three to five years and can be repeated. SLT is replacing eyedrops in some cases.
  • Trabeculectomy. This is a type of surgery that creates a new drainage pathway for the aqueous humor.

There’s no cure for open-angle glaucoma, but early diagnosis can help you avoid most of the dangers of vision loss.

Even with new laser treatments and surgeries, glaucoma requires lifetime monitoring. But eyedrops and new laser treatments can make glaucoma management fairly routine.

Seeing an eye specialist once a year is the best prevention for open-angle glaucoma. When glaucoma is detected early, most of the adverse consequences can be avoided.

Open-angle glaucoma shows no symptoms in the early stages, so regular eye examinations are the only way to find out if it’s developing. It’s best to have an eye exam with an ophthalmoscope and dilation performed once a year, especially if you’re over 40.

While a good diet and a healthy living style may provide some protection, they’re no guarantee against glaucoma.