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Cannabis and Glaucoma - Then and Now

Glaucoma is known all over the world as one of the more serious causes of permanent and total blindness. While effective medical treatment options do exist, many glaucoma sufferers find them to be either useless for their condition or simply too expensive and out of their reach.

Thankfully, other, more affordable treatment options do exist, one of which is the usage of medical marijuana or cannabis. Along with its relaxing and psychoactive effects, marijuana has been proven to also have significant therapeutic benefits that can alleviate or manage certain conditions thought to be difficult to treat, glaucoma being one of them.   

In fact, the rise of cannabinoid use has its origins as treatment for glaucoma. Many patients have always inquired about the use of medical cannabis when all glaucoma medications have failed them. But why has cannabis grown to become the go-to drug for patients with glaucoma? Is it really as effective as advertised, or does it offer a placebo effect to its users instead?

History

It was 1971 when reports surfaced that the smoking of marijuana potentially lowered levels of IOP—Intraocular Pressure. Since then, cannabinoids have been catapulted into near-mythic status for being a miracle drug for glaucoma. When the age of medical marijuana started to blossom in 1974, a patient named Robert Randall saw that the lights and haloes he experienced due to his severe glaucoma would disappear whenever he smoked marijuana. He was then faced with federal criminal charges for planting and growing marijuana for his medical use, but he won the case. The federal judge was even persuaded to deem that marijuana use was a medical necessity.

Since then, many states have legalized the use of cannabis for medical purposes. It all started with California in 1996, growing to about 29 states and Washington, DC to date. Its legislation is introduced annually in remaining states, however it is still classified as a Schedule I controlled substance that retains a high potential for abuse. 

What is Glaucoma?

Glaucoma is a group of diseases to the eye that damages the nerve that is responsible for relaying visual information to the brain. Untreated, the visual information never reaches your brain, which causes eventual blindness. It has been recognized as one of the leading causes of permanent visual impairment and visual loss. In some cases, it can lead to complete and total blindness.

One of the main causes of glaucoma is an increased pressure to the eye that damages nerve fibers and blood vessels. This increased pressure is called intraocular pressure, or IOP. Normally, the fluid inside your eye, which is called aqueous humor, flows out of your eye through a mesh-like channel. If this channel gets blocked, the liquid builds up, and IOP in the eye increases. The reason why this channel is blocked is often unknown, but many doctors agree that it can be inherited. This means that children of glaucoma sufferers have an increased chance of getting the condition themselves sometime in their lives.

There are two types of glaucoma:

  • Open Angle Glaucoma – This is the most common type of glaucoma worldwide. In this kind of glaucoma, the mesh-like channel—called the trabecular meshwork—looks normal upon examination, but fluid doesn’t flow through it like it normally should. This causes increased IOP and thus nerve damage.
  • Closed Angle Glaucoma – the fluid passage is blocked even before it reaches the area of drainage, likely to a small distance between the iris and the lens. When they come into contact with one another, the fluid will be unable to pass, which in turn leads to an increased pressure. This condition is more common in Asia rather than in the West, and is linked to farsightedness and cataracts/

There is also evidence that suggests glaucoma is connected to other neurodegenerative diseases such as Alzheimer’s disease. One out of four patients with Alzheimer’s disease has glaucoma, which is in turn a predictor of Alzheimer’s disease. 

Research And Studies Show That Cannabis May Be Able To Help With Glaucoma.

Who is at risk for Glaucoma?

Glaucoma is known to affect middle- to old-age adults, usually over 40. However, young adults, children, and even infants are known to contract this condition. African-Americans are also more at risk of developing glaucoma at a young age and with greater loss of vision than any other race.

Besides this, some factors that increase the risk of glaucoma include the following:

  • Race. Those of Irish, Russian, Hispanic, Japanese, Inuit, or Scandinavian descent are known to have a higher chance of suffering glaucoma during their lifetimes.
  • Family history. Those with first-degree relatives who suffered from glaucoma are at an increased risk of contracting the condition themselves.
  • Poor vision. Individuals suffering from common vision issues may also be more at risk of contracting glaucoma.
  • Diabetes. Untreated diabetes can wreak havoc on many organs of the human body, the eyes included. Eye damage caused by untreated diabetes can easily lead to glaucoma.
  • Certain medications. The regular intake of certain medications such as prednisone or other steroids can present a higher risk of glaucoma.
  • Trauma. Blunt-force damage or trauma to the eyes can also cause glaucoma or the delayed onset of the condition if improperly treated.

Surgical procedures and treatments have improved drastically and significantly since 1980, which has cut the risk of irreversible blindness in half. However, as the treatment improves, the collection of effective topical solutions remains as limited as ever. Cost of treatment is also a significant concern, one that’s compounded with the lack of affordable healthcare and/or health insurance among the public. Cannabis is recognized almost universally as a treatment for glaucoma in medical cannabis states, but should this really be the case? Or should the public be dissuaded from seeing it as a viable alternative? 

Cannabis and Glaucoma

Cannabis is a combination of the dried up tops and flowering leaves of the plant known as Cannabis Sativa. THC (Delta-9 tetrahydrocannabinol) was identified and isolated as its most active component back in 1964, and is notorious for its psychoactive effects on users. Cannabis also has at least 400 known chemicals, whose related compounds are called cannabinoids.

Cannabis, as well as THC was shown to decrease IOP in up to 65% of normal individuals, as well as glaucoma patients. Studies in 1971 show that ingestion of cannabinoids lowered IOP by up to 30%. However, despite early research findings, there still remain very few ophthalmologists that support medicinal cannabinoid use for patients that have early to mid-stage glaucoma. The foremost issue is the potentially adverse side effects of cannabis—especially by smoking—that largely outweigh its short-term benefits. One example is that the act of smoking itself leads to unstable IOP, which increases the risk of blindness. Another example include the contraction of serious conditions such as cancer of the respiratory organs.

Since the therapeutic effects of cannabinoids on glaucoma are relatively short-term, this means that patients would have to consume cannabis more frequently—as frequent as every three hours. This frequency has a tendency to be unsustainable, and could lead to the development of cannabis use disorder.

Opinions tend to shift when it comes to late-stage glaucoma, however. Ophthalmologists are more welcoming to cannabinoid use towards the later stages of glaucoma as it’s more about alleviating accompanying symptoms rather than directly targeting glaucoma itself.

 

The exact mechanism of cannabis is yet unknown, but cannabinoid receptors have been located in the trabecular meshwork, ciliary muscle, and non-pigmented ciliary epithelium of the human eye. One study of aqueous humor dynamics shows that smoking cannabis actually improved uveoscleral outflow.  

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Alternative Uses

Smoking cannabis is not the only way of getting cannabinoids into your body to access their therapeutic benefits. Alternative methods include ingestion, cannabis oil, vaporization, as well as topical solutions. Since the cannabis plant has hundreds of cannabinoids that each have varying effects, medication and delivery can differentiate effects per strain.

  • Vaporization and/or Ingestion – this can sometimes be seen as an improvement over smoking cannabis as it avoids the toxicity of combustible by-products, the long-term use of which can be more damaging health-wise to patients.
  • Topical Administration – Eye drops, and other more localized and topical administrations such as cannabis oil is another potential solution. It reduces the probability of activating the body’s other cannabinoid receptors, which often lead to unwanted side effects.

Limitations of Cannabis for Glaucoma

Although the therapeutic effects of cannabis cannot be so easily dismissed, it has an alarming number of side effects for glaucoma patients who would be required to use it heavily. It can cause tachycardia and a decrease in blood pressure, thereby reducing the flow of blood to an already affected optic nerve. Aside from raising the risk of lung cancer, heavily smoking cannabis can lead to a variety of serious ocular and systemic side effects:

  • Ocular – Conjunctival hyperemia; decreased lacrimation; ptosis; photophobia; nystamagus, blepharospasms, accommodation impairment.
  • Systemic – Decreased blood pressure, tachycardia; orthostatic hypotension; either euphoria or dysphoria; decrease in testosterone; impaired immunity; difficulties with focus, memory, and solving problems.

The limitations of cannabis use for treating glaucoma led several ophthalmic organizations to oppose its use in treatment. In 2009 and 2014 alone, the American Academy of Ophthalmology’s Complementary Therapy Task Force said that there is no scientific evidence that demonstrate heightened benefits and less risk in treating glaucoma. 

The Future of Cannabis-Based Treatments for Glaucoma

The body’s endocannabinoid system or ECS is among our most important physiological systems. It affects many crucial aspects of our health including our immune response, inflammation, pain modulation, and neuroprotection. This vital role in our systems (when the body consumes cannabinoids, it affects our endocannabinoid system) leads scientists to believe that developing cannabinoid-based medications could lead in a breakthrough in the treatment and prevention of glaucoma.

The brain’s cannabinoid receptors are very prominent in the ocular tissues that regulate IOP. One area of research could be to develop specific cannabinoid-based medicines that target these tissues themselves, thereby lowering IOP, and protecting the retinal cells.

Studies suggest that there are actually some great candidates in cannabis to develop as therapeutic agents. These include two cannabinoid agonists: WIN 55212-2 and anandamide, as well as several cannabinoids that include cannabidiol (CBD) and cannabigerol (CBG). These compounds carry the therapeutic effects of cannabis without retaining the addictive and often excessively psychoactive qualities of THC, and are already in use today in milder cannabinoid medications such as cannabis oil. Administered topically—even directly onto the eye as medicated eye drops—they turned out effective and well tolerated.

Challenges still remain, however, and these are not unique to the use of cannabis. Oral medication if seen as a poor method as bioavailability is sub-par, and absorption is tricky and unpredictable. Inhalation via smoke is not ideal either, as the effects, though good, don’t last very well and require constant use, to the debilitation of the patient’s lifestyle and mobility. This leaves the possibilities open for topical preparations, which currently perform weakly—despite being a better method compared to oral and inhalation—when it comes to penetrating intraocular tissues, with up to 95% of administered dosages failing to reach their intended mark. 

Conclusion

While the therapeutic use of cannabis may be tempting, and has been a go-to cure for glaucoma, patients who inquire about its usage should be properly counseled. The drug does lower IOP, but it has many significant limitations as well, including short term benefits, variety in potency, a number of side effects, tolerance development, and health risks especially when consumed through smoke inhalation. Patients often take it as an adjunct form of therapy, but not as the primary treatment, as modern glaucoma medications have proven to be more consistent with the lowering of IOP, has even fewer side effects, and has a longer duration of action. For a better, longer term monitoring of glaucoma, patients are advised to continue to adhere with their prescribed therapy.