There are two main categories of glaucoma, open angle and closed angle glaucoma.
What Is Glaucoma?
Glaucoma is a disease of eye pressure that affects the optic nerve in the back of the eye. The optic nerve is an extension of brain tissue. Once the optic nerve is damaged, the damage cannot be reversed. If the eye pressure inside of your eye is too high for your optic nerve, it can lead to blindness. In most cases, glaucoma has no symptoms until it is in its later stages. There are two main categories of glaucoma, open angle and closed angle glaucoma. The most common type is open angle glaucoma.
Glaucoma is a disease that damages the optic nerve. Glaucoma is associated with higher pressure inside the eye than is healthy for the optic nerve. This occurs when the aqueous humor, cannot easily flow out of the eye. Too much pressure within the eye can damage the optic nerve, initially creating loss of the peripheral vision, small and unnoticed by the patient at first, becoming larger and ultimately leading to blindness. Early detection and treatment are critical to preventing damage to the optic nerve.
There is no one correct or ideal eye pressure as this varies person to person. Once the optic nerve has been damaged it cannot be repaired and the vision loss cannot be reversed. In most cases, patients will not suffer any symptoms until the disease has advanced to the later stages. Regular eye exams are key to detecting glaucoma and to maintaining the best possible vision.
SYMPTOMS OF GLAUCOMA
At early stages, most people do not suffer from symptoms of the two main types of glaucoma.
Open angle glaucoma is progressive with loss of the peripheral (side) vision. Symptoms include:
- Subtle loss of peripheral vision at first and often unnoticed in day-to-day activities.
- As the optic nerve becomes more damaged, the areas of decreased vision progress to blind spots. It can still be unnoticed in most day-to-day activities at this stage.
- Encroachment on the central vision.
- Blindness - ultimately, as more of the optic nerve is choked off and dies, blindness occurs.
Angle closure glaucoma results from a narrowing of the angle of the front of the eye. Initially there are no symptoms, but over time, this progresses to angle closure, and if symptoms are present they may include:
- Blurry vision
- Rainbow-colored halos around lights
- Severe eye pain
- Nausea and vomiting
- Headache or brow pain
Types of Glaucoma
There are two main types of glaucoma: open angle and closed angle glaucoma. Closed angle glaucoma is also called angle-closure glaucoma or narrow angle glaucoma.
Open Angle Glaucoma
The most common type of glaucoma is open angle glaucoma. In this form of glaucoma, the part of the eye called the angle is open to receive natural fluid that circulates inside the eye. The aqueous humor is full of nutrients the inside of the eye needs for optimal health and is produced behind the pupil, circulating through the pupil, over the iris to the angle of the eye where it exits in small amounts as new aqueous is created. Open angle glaucoma occurs when the aqueous produced by the eye isn’t absorbed or drained quickly enough so eye pressure increases. Each patient has a different ideal eye pressure; there is not one “right” eye pressure that is the same for each person.
Our goal is to keep the eye pressure for each individual at a level that will help protect the optic nerve from further damage. As there are often no symptoms of this type of glaucoma until the disease has progressed, it is usually only discovered during a routine eye exam. Vision loss from open angle glaucoma tends to happen slowly and generally affects the peripheral vision first. If this condition is not treated, it will result in blindness.
There are many types of open angle glaucoma including:
Primary open angle
Normal-tension glaucoma is also called low-tension glaucoma. This happens when optic nerve damage occurs despite normal eye pressures. Eye pressure is measured in millimeters of mercury (mmHg). A reading of less than 21 mmHg is considered to be “normal,” but this can be misleading in patients with normal-tension glaucoma, as damage to the optic nerve occurs at these pressures. Because vision loss can still occur even though eye pressures are in a “normal” range, eye pressure alone is never used to monitor for glaucoma. This condition is treated the same way as open angle glaucoma.
Closed Angle Glaucoma
Closed angle glaucoma occurs when the front structures of the eye are too crowded together. In this form of glaucoma, the part of the eye called the angle is closed or too narrow to receive natural fluid that circulates inside the eye. This fluid (called aqueous) is full of nutrients the inside of the eye needs for optimal health. It is produced behind the pupil, circulates through the pupil, over the iris to the angle of the eye where the fluid exits in small amounts as fresh aqueous is created. Closed angle glaucoma occurs when the fluid inside the eye cannot reach the drainage angle and the eye pressure increases as more fluid is made but cannot exit the eye. Closed angle glaucoma often causes sudden blurry vision and discomfort or pain in and around the eyes. Sometimes, however, this form of glaucoma can proceed slowly without pain or blurry vision, and can slowly damage the optic nerve and lead to vision loss. This is called chronic angle closure glaucoma.
Symptoms of closed angle glaucoma range from no symptoms to eye pain and redness, blurry vision, headaches, vomiting, and halos/rainbows in the vision. If this condition is not treated, it will cause blindness.
Narrow Angles: A precursor to closed angle glaucoma
Some patients have a narrow drainage angle in the eye that predisposes them to develop closed angle glaucoma. This condition is diagnosed during a routine eye exam. If the drainage angle is very narrow and at high risk for closing off, a laser procedure called a laser peripheral iridotomy (LPI) is recommended. Most patients report they feel very little sensation during this office procedure.
Combined Mechanism Glaucoma
Some patients may have a combination of both types of glaucoma, or precursors to both types of glaucoma. In that case, both conditions are monitored closely or treatment may be recommended for one or both.
Occasionally the thickness of the lens of the eye (a cataract or early cataract) causes pressure on the optic nerve and results in damage. Removing the lens/cataract relieves the pressure and halts the damage.
Glaucoma is the second leading cause of blindness in the U.S. and the leading cause of preventable blindness.
It is the number one cause of blindness in people over age 60 in the United States. Three million Americans have glaucoma, but only half of them know it.
Glaucoma, in most cases, can only be detected by routine eye exams. During a routine exam, a screening for glaucoma is performed, which consists of measuring eye pressure, checking the front drainage angle of the eye, and examining the optic nerves. If glaucoma is suspected, further tests to measure the shape and function of the optic nerve are performed. Patients are considered “glaucoma suspects” if during the exam there are findings that are suspicious for glaucoma. This diagnosis means patients will be watched carefully for changes to eye pressure and damage to optic nerves.
GLAUCOMA RISK FACTORS
As one ages, there is an increased risk for developing glaucoma, although younger people may have it as well.
The risk for open angle glaucoma is higher for individuals who have:
- Relatives with glaucoma as heredity and ethnicity may play a part in determining the risk for developing glaucoma and what subtype a patient may have
- Poor circulation
- Previous eye injuries
- A thinner central corneal thickness
- Increased “cupping” in the optic nerve, which is an enlargement of the central depression of the optic nerve.
The risk for closed angle glaucoma is higher for individuals who have:
A thicker lens
There are several treatments available depending on the type of glaucoma and an individual’s lifestyle factors. Treatments may include eye drop medication(s), office based laser surgery, or surgery in the operating room.
Eye drops work to lower eye pressure by either increasing the outflow of fluid inside the eye or by slowing the production of fluid made inside the eye. These medications are used long term and just like any other prescribed medication, need to be taken as prescribed, one-to-three times per day. For patients who have difficulty using drops or experience side effects from the drops, other treatment options may be available.
Laser Treatment for Open Angle Glaucoma
Selective Laser Trabeculoplasty (SLT) is a gentle laser option to treat open angle glaucoma. In SLT, a low energy laser targets the drainage part of the eye located in the angle in the front of the eye. It stimulates the angle cells to function more efficiently. No holes are created. This painless office procedure takes only minutes to perform. Because of the effectiveness and long-term safety profile, SLT is often a first line treatment option instead of eye drops.
SLT alone is as effective as eye drop therapy and doesn’t require remembering to use an eye drop on a regular basis, nor have side effects as eye drops may. The procedure may decrease or eliminate the need for eye drops to control glaucoma in many individuals. SLT can also be used as an additional therapy to eye drops. The effectiveness lasts months in some patients and decades in others and can be repeated. (Wong MO et al, 2015; Avery N et al, 2013)
Laser Treatment for Narrow Angles or Closed Angle Glaucoma
Laser peripheral iridotomy (LPI) is recommended for patients with narrow angles at risk for closure or closed angle glaucoma. A laser is used to create a small hole in the iris in order to allow fluid better access to the drainage angle. Most patients report feeling very little sensation during this office procedure.
If the damage from glaucoma is advancing despite maximal medical (drop) treatment and laser surgery therapy, a trabeculectomy, aqueous shunt procedure, or micro-invasive glaucoma procedure is recommended. During this outpatient procedure, microsurgical instruments are used to create an alternative way for aqueous fluid to exit the eye. Occasionally cataract surgery or lens removal is recommended when the thickness of the lens of the eye causes increased eye pressure that is not resolved by drops or laser, or when it is causing pressure on the optic nerve (phacomorphic glaucoma), or when it is causing narrow angles.
Foods, diets, supplements, exercise, and alternative medicine have not been shown to alter intraocular eye pressure. (Rhee DJ et al, 2001) And despite popular belief, extensive research over many decades concludes that marijuana is not effective in the management of glaucoma for the following reasons:
Smoked marijuana doesn’t lower the eye pressure in a majority of patients. In those in which it is effective, the effects are short-lived (three-to-four hours) and modest at 25%.
As the eye pressure lowering effect of marijuana wears off, the detrimental effects of eye pressure on the optic nerve return. In order to keep the eye pressure consistently down and prevent the eye pressure fluctuating up and down, marijuana would have to be smoked every three-to-four hours around the clock, interfering with sleep and causing impairment for tasks requiring any amount of attentiveness or concentration.
Other routes for the delivery of marijuana to lowering eye pressure have been even less successful than smoking. In topical (eye drop) formulations, marijuana did not penetrate the eye well, and edibles had variable absorption from the gastrointestinal track resulting in even less successful eye pressure lowering. (Flach AJ, 2002; Flom MC et al, 1975; Green K, 1998; Hepler RS & Frank IR, 1971; Kaufmann P, 1998)
What The Patient Can Do
Glaucoma is a chronic long-term disease and requires close teamwork, regular office visits, and honest communication between patient and doctor. Typically a patient can expect a visit with the eye doctor every three-to-six months, to monitor for any progression of the disease requiring changes in treatment. Topical or drop therapy is almost always a long-term treatment. As with all medicines, the patient must be dedicated to following instructions and should be open and honest if this is not done. Reporting any side effects is also important. Only then can the eye doctor monitor and adjust treatment to prevent loss of vision.
Avery N, et al. 2013. Repeatability of primary selective laser trabeculoplasty in patients with primary open-angle glaucoma. International Ophthalmology : The International Journal of Clinical Ophthalmology and Visual Sciences, v33 n5: 501-506
Committee of the Health Effects of Marijuana: An Evidence Review and Research (2017) The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Health and Medicine Division of National Academies of Sciences, Engineering, and Medicine. nationalacademies.org/CannabisHealthEffects.
Flach AJ. 2002. Delta-9-tetrahydrocannabinol (THC) in the treatment of end-stage open-angle glaucoma. Transactions American Ophthalmological Society, no 100: 215–224
Flom MC, et al. 1975. Marijuana smoking and reduced pressure in human eyes: drug action or epiphenomenon? Investigative Ophthalmology, 14 (1): 52–55
Green K. 1998. Marijuana smoking vs. cannabinoids for glaucoma therapy. Archives of Ophthalmology, 116 (11): 1433–1437
Hepler RS, Frank IR. 1971. Marihuana Smoking and Intraocular Pressure. JAMA, 217 (10): 1392
Kaufmann P. 1998. Marijuana and glaucoma. Archives of Ophthalmology, 116 (11): 1512–1513
Rhee DJ et al. 2001. Complementary and Alternative Medicine for Glaucoma. Survey of Ophthalmology, v46 n1: 43-55
Wong MO, et al. 2015. Systematic review and meta-analysis on the efficacy of selective laser trabeculoplasty in open-angle glaucoma. Survey of Ophthalmology, Jan-Feb; 60(1): 36-50