What Is Open Angle Glaucoma?

Published July 7, 2020

Open-angle glaucoma accounts for more than 80% of all glaucoma cases.

Open angle glaucoma (OAG) is the most common form of glaucoma that usually progresses slowly over time. This type of glaucoma generally does not cause any pain or other noticeable symptoms.

Open angle glaucoma is nicknamed ‘the silent thief of sight’ because by the time the disease is detected, a large amount of irreversible damage to the optic nerve has already occurred, causing permanent vision loss.

Open angle glaucoma usually affects people above the age of 40.  It generally affects both eyes, though one eye more than the other.

  • It is estimated that 2.7 million Americans, above the age of 40, are affected by open angle glaucoma. 
  • Glaucoma affects up to 5% of adults ages 70 and above, and increases to over 9% for those 80 and older.

    Unfortunately, there is no cure for glaucoma. Without treatment, total vision loss can occur, leading to permanent blindness. The most important way to prevent vision loss is through early detection— having regular eye exams, especially if you are above the age of 40.

    Why is it called ‘open angle’ glaucoma?

    Your eyes are constantly producing a fluid, called aqueous humor. This fluid is important for many different reasons, and is responsible for:

    • Lubricating the muscles and fibers of the focusing lens
    • Supplying nutrients and oxygen to the back of the cornea
    • Clearing away waste products from the cornea
    • Maintaining the shape of the cornea

    In a healthy eye, the fluid continuously moves through the eye— as fluid drains out, new fluid is produced. This system must be kept in balance in order to maintain normal IOP.

    The anterior angle of the eye is where the clear part (cornea) meets the colored part (iris). The angle is responsible for draining the fluid that is produced within the eye— sending it from the eye through the uveoscleral drains and trabecular meshwork, and down the back of the nose and throat.

    In open angle glaucoma, the angle is wide open, for an easy outflow of fluid through the uveoscleral drains. However, the fluid is unable to drain effectively through the trabecular meshwork— usually due to either a blockage, or overproduction of aqueous humor. This causes the fluid to drain more slowly and consequently raises your IOP.

    If your IOP remains high, between 15-25 mm Hg,for an extended period of time without treatment, the pressure will continuously push on the optic nerve, causing damage— and consequently, permanent vision loss.

    Symptoms of open angle glaucoma

    While in its early stages there are no symptoms that allude to a problem, later symptoms may include:

    • Reduced vision
    • Loss of peripheral vision
    • Bulging or swollen cornea
    • Pupil dilation that doesn’t change with light adjustments
    • Redness in the white (sclera) of the eye
    • Nausea

    Loss of peripheral vision is the first stage of vision loss caused by open angle glaucoma. If the disease is not effectively controlled at this stage, the disease can cause a condition called ‘tunnel vision’, which limits your field of vision to strictly seeing images that are in your central vision, or straight ahead.

    As glaucoma progresses into a more advanced stage, loss of central vision will occur as well— resulting in partial or complete permanent vision loss.  

    Who is at risk of developing open angle glaucoma?

    • Older age, above 40
    • Family history of glaucoma
    • African ancestry
    • Nearsightedness
    • High IOP
    • Low blood pressure
    • Topical corticosteroids
    • Ocular inflammation
    • Ocular tumor

    If you are at risk of developing open angle glaucoma, it is crucial for your eye doctor to monitor your ocular health. 

    How is open angle glaucoma treated?

    Anti-glaucoma eye drops

    Most cases of open angle glaucoma can be controlled with eye drops.

    There are many types of anti-glaucoma eye drops, each type works differently to control IOP.

    Different types of anti-glaucoma eye drops:

    • Prostaglandins relax the muscles in the eyes to allow better fluid drainage, reducing build-up of IOP.
    • Beta-blockers are used in a variety of glaucoma eye drops. They decrease the amount of ocular fluid production and are often prescribed in combination with prostaglandins.
    • Alpha-adrenergic agonists decrease the rate of fluid production. They can be used alone or in combination with other anti-glaucoma eye drops.
    • Carbonic anhydrase inhibitors decrease the rate of fluid production, and are used in combination with other anti-glaucoma eye drops
    • Parasympathomimetics are very often used to control IOP in narrow-angle glaucoma. They work to increase ocular fluid drainage by opening the narrow angle where drainage occurs.
    • Epinephrine decreases the rate of ocular fluid production, and increases its outflow from the eye.
    • Hyperosmotic agents are used in emergencies, for patients with a severely high IOP that must be reduced immediately before permanent damage occurs. They reduce IOP by lowering ocular fluid volume.
    • Combination glaucoma drugs include two different anti-glaucoma medicines. Many times, patients with glaucoma require more than one type of medication to control IOP.

    Laser surgery

    In some cases, laser surgery may be recommended. During a laser surgery procedure, different avenues are created to increase fluid drainage, and reduce IOP.

    Selective laser trabeculoplasty (SLT) is the primary laser surgery performed for open angle glaucoma. This laser procedure stimulates a biochemical change that improves the fluid drainage from the eye.

    Selective laser trabeculoplasty effectively lowers IOP by 20 to 30 percent, and has been proven just as effective as anti-glaucoma eye drops. Improved IOP after an SLT treatment has been shown in about 80 percent of patients, and may last 3 to 5 years. This laser surgery can also be repeated if needed.

    Minimally invasive glaucoma surgery (MIGS)

    Minimally invasive glaucoma surgery (MIGS) uses microscopic tools and devices to lower the risk of surgical complications.

    Micro trabeculectomies

    Micro trabeculectomies involve implanting a microscopic tube, using an iStent, Xen Gel Stent, or PRESERFLO, into the eye to enable proper fluid drainage through the anterior angle.

    The iStent is typically used for mild to moderate open angle glaucoma.

    The iStent procedure reduces IOP levels by creating a bypass through the anterior angle to improve the outflow of fluid from the eye— through its natural drainage system.

    Benefits of iStent:

    • Generally combined with cataract surgery— improving IOP with minimal use of pressure lowering eye drops
    • Causes minimal damage of normal eye tissue
    • Easier to perform, faster to recover from, and safer than many glaucoma surgeries
    • May reduce medication burden— including cost, inconvenience, and side effects
    • May delay or prevent additional surgical interventions in the future

    Glaucoma filtration surgery

    This type of surgery is recommended for mild to moderate stages of glaucoma, if eye drops and laser surgery have not been able to effectively lower IOP. 

    During this procedure, a tiny piece of the wall of the eye is removed, in order to create another drainage pathway. The ocular fluid can then effectively drain out of the eye through this new drainage system, thereby lowering IOP levels.

    When to see your eye doctor

    If you are concerned about your vision and ocular health, schedule a comprehensive eye exam. Your eye doctor can detect signs of glaucoma in its earliest stages, and prescribe an effective treatment to help prevent vision loss.