Cannabis and CBD oil: a new “old” friend in optometry


What do CBD, cannabis, and marijuana have do with with optometric care? Find out.

Optometric training requires learning about bones, muscles, neurology, and the vascular and other systems. But have you heard of the endocannabinoid system (ECS)?

If the answer is no, that’s not surprising.

Robert Reed Jr,OD

Although the ECS is critical for human survival,1,2 cannabinoid receptors weren’t identified until 1964,1-4 when investigators were trying to locate where marijuana tetrahydrocannabinol (THC) interacted with the brain. It wasn’t until 1988 that the ECS was identified, and 1992 when it was officially acknowledged.2-4

Humans operate on the parasympathetic and sympathetic system. The parasympathetic system operates under “normal” conditions.
When the body perceives it is under attack, neurochemicals trigger the sympathetic system, activating the “fight or flight” response.5,6

Figure 1. The CB1 and CB2 receptors of the endocannabinoid system can be found throughout the body.

The ECS, simply put, disengages the sympathetic system. It is responsible for bringing the body back into balance (homeostasis).2,7 If it doesn’t, the body is faced with unresolved “danger” from the chemicals and processes that are designed to protect it. These chemicals cause inflammation and begin attacking and damaging the body,7,8,9 which is then labeled as “such and such” disease. Our rampant, epidemic health problems are self-inflicted,5,7,10 brought on by our diet, lifestyle, and technology.7,10,11

The ECS (Figure 1) is made up of 2 main receptor sites, CB1 and CB2.2,4,7,10

CB1 sites are primarily in the brain, heart, and lungs, and modulate the immune response. CB2 receptors are primarily located in the lymph system, detoxification organs, and peripheral systems to break down and clear out the toxic immune system chemicals and debris.1,3,7,14,24

The body produces its own chemical—anandamide, known as the bliss chemical—to regulate our systems via the ECS.7,13,14 Unfortunately, in today’s high-stress environment, it can’t create enough to keep up with the demand.10,14

Eating dark chocolate, exercising, or being “in the zone” are other ways to feed the CB1 and CB2 receptors.7,14 Cannabidiol (CBD) was removed from livestock feed when it was made schedule 1 in 1941, so it has not been in the food chain for 80 years. CBD is nature’s external equivalent to supplementing the body’s anandamide shortage.17,18,24


Technically, cannabis is not marijuana; nor is CBD. Cannabis is the botanical name for the common hemp plant, which has been cultivated for industrial purposes for more than 20,000 years.15,18,24

The medicinal properties of hemp have been utilized for over 10,000 years.15 The 2 main classes of cannabis are sativa, which is generally stimulating, and indica, which is generally calming.16,18

Figure 2. Tetrahydrocannabinol and cannabinoid molecular formulas.

Marijuana is a small subset of hemp that has been bred to produce more “high.” Hemp has over 400 different chemicals, with 100 compounds known as cannabinoids, each creating various effects.16,18

CBD is one of the most prevalent cannabinoids in the hemp plant; it has the most profound, diverse, and beneficial impact.16,18 The main takeaway is that cannabis is really just the hemp plant, and CBD is not marijuana.


THC and CBD originate from the same compound and have nearly identical chemical structures (Figure 2).16,22 Depending on the genetic strain, the hemp will have higher or lower THC and CBD levels. When the flower is beginning to bloom, however, growers must test the plants daily because the CBD in the plant will start to become THC.16,22

At that point, the growers only have 48 hours to harvest their crop. The legal amount for THC to not be considered marijuana is 0.3%.19,22

Figure 3. The benefits of using cannabinoids on the endocannabinoid system. (All images courtesy of Robert Reed Jr, OD.)

The CBD industry wants as high an amount of CBD as possible with the least THC possible. CBD’s profound effects on all bodily functions are not forced—unlike those of pharmaceutical agents—and nor does the chemical have their toxicities or unintended adverse effects (Figure 3).20,21,24

As of February 2022, 37 states in the United States have legalized marijuana for medical use and 18 have legalized it for recreational purposes.20 The medical and recreational marijuana market is projected to be $30 billion in 2022.21

Although marijuana still has legal hurdles to overcome, the CBD market is legal in all 50 states.22 CBD is also available OTC and thus is free from FDA regulations and red tape.22 The CBD market is projected to be $2 billion in 2022.23

This projection will result in both good and bad consequences. Because cannabis has been outlawed as a Schedule 1 drug for 80 years, little controlled research has been undertaken and no distinction made between the effects of THC and those of CBD.

Medical benefits, risks

Much of marijuana use is for the high it produces, but there are some documented medical benefits. These include the relief of pain and nausea related to cancer treatments, aiding of sleep issues, reduction of posttraumatic stress disorder symptoms, easing of symptoms in those withdrawing from opioid addiction, and a calming of symptoms of various neurological conditions.4,24

Unfortunately, according to more recent findings, marijuana does interfere with cognitive ability,24,29 damages memory function, and destroys brain tissue. It also causes heart attacks—even in younger people with no underlying conditions—may have negative effects on genetics and pregnancy, and, if ingested by vaping or smoking, increases cancer risks.24 Thus, marijuana is far from risk free.

Vision effects

Of more direct concern to optometrists are the negative effects of marijuana on the visual system. Both photopic and scotopic vision are impaired due to decreased macular and peripheral sensitivity.24-35

Neurologically, vision processing is compromised, creating selective scotomas and interfering with one’s ability to navigate in the environment.24,26-28,30,32-35

The eye is both a specialized neurologic receptor and a person’s primary connection to the physical world. It is important for optometrists to be aware of CBD, as eyes are packed with both CB1 and CB2 receptors.

Consider the major 5 medical conditions optometrists often encounter with when working with patients:

1. Cataracts37

2. Glaucoma38,39

3. Macular degeneration41-43

4. Allergies46

5. Meibomian gland disease47

Although each is a separate condition, all have inflammation as the root cause due to the eye being threatened by the environment.35,40 Many treatments are based on treating the symptoms or slowing the progression of damage by interfering with the ocular response process.

CBD works with the body’s natural system to decrease the inflammation process and restore homeostasis, avoiding the long-term results that define disease.

Peer-reviewed, evidence-based science is limited. However, I have heard anecdotally that some patients have experienced better vision with OTC supplementation of CBD and ocular nutraceuticals, backed by macular pigment ocular density (MPOD), optical coherence tomography (OCT), retinal photographs, and acuity.43,44

Looking ahead

We have accepted that ocular “aging” conditions are normal, inevitable, and unstoppable.45,57 Perhaps traditional medical treatments would be less necessary if we worked with the natural body system designed to minimize those issues.

Beyond ocular conditions, optometrists must step back and look at the larger medical issues facing humanity.

Obesity, diabetes, blood pressure, heart disease, cancer, Alzheimer disease/dementia, autoimmune conditions (lupus), rheumatoid arthritis, fibromyalgia, multiple sclerosis, neurologic disorders, depression, anxiety, panic attacks, migraines, attention-deficit/hyperactivity disorder, and concussions are all inflammation-related processes caused by an increased assault on our physical system.

This has overloaded the natural mechanism eyecare professionals were designed with to maintain health. Optometrists need to learn about ECS and CBD to augment their toolbox for taking care of patients’ well-being.6,9,36,48,51,55,56,59-63


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