Ocular Disease and Eye Function – Medical Cannabis for the Treatment of Macular Degeneration

Nature has many ways of making it hard for people to see. As we age, we notice subtle little signs that tell us that our vision is changing. Perhaps you need glasses to see up close or you have trouble adjusting to glare or distinguishing some colours. These changes are a normal part of ageing. They should not stop you from enjoying an active lifestyle or stop you from maintaining your independence. In fact, many people can live an active life well into their golden years without ever experiencing severe vision loss. But, as you age, you are at a higher risk of developing age-related diseases and conditions. They include age-related macular degeneration, cataracts, diabetic eye disease, glaucoma, low vision and dry eyes.

AGE-RELATED MACULAR DEGENERATION (AMD)

AMD is a common eye condition and a leading cause of vision loss among people aged 50 and older. It causes damage to the macula, a small spot near the centre of the retina and the part of the eye needed for sharp, central vision, which lets us see objects that are straight ahead.

In some people, AMD advances so slowly that vision loss does not occur for a long time. In others, the disease progresses faster and may lead to a loss of vision in either one eye, or both eyes. As AMD progresses, a blurred area near the centre of vision is a common symptom. Over time, the blurred area may grow larger or you may develop blank spots in your central vision. Objects may also not appear to be as bright as they used to be.

AMD itself does not lead to complete blindness. However, the loss of central vision in AMD can interfere with simple, everyday activities, such as the ability to see faces, drive, read, write, or do work that require up-close vision.

THE MACULA

The macula is responsible for focusing the central vision of the eye.  Without the macula, we couldn’t recognise colours or faces, which would make us unable to drive, read or see objects in detail. With macular degeneration, the macular generally deteriorates. As the cells begin to fail, images aren’t received properly, leading to blurred and distorted vision. Eventually, a blind spot will develop in the centre of a patient’s vision. As MD progresses, the blind spot expands until all central sight is completely lost, although peripheral vision remains intact.

Macular degeneration occurs in two basic type – dry and wet MD.

  1. DRY MACULAR DEGENERATION

Almost all MD is considered dry, or atrophic – around 85 to 90% of macular degeneration cases fall into this category.  In dry MD, blood serum doesn’t leak into the retina.  Instead, the deterioration of the macula is due to small, yellow deposits of amorphous and acellular debris called drusen.  The formation of drusen causes the macula to thin and dry out, which ultimately leads to loss of function.  Almost all people over the age of 50 will have at least some drusen in their retina, but only large drusen deposits lead to MD.  Dry MD tends to progress more slowly than wet MD and vision loss is often less serious.

  • WET MACULAR DEGENERATION

Wet or exudative macular degeneration occurs in roughly 10 to 15% of MD cases.  This form progresses rapidly, often leading to severe vision loss and impairment.  In wet MD, abnormal blood vessels called choroidal neovascularization (CNV) form under the retina.  As they grow, CBN vessels tend to bleed and leak fluid into the macula.  This influx of fluid makes the macula lift or bulge – which damages and distorts central sight.  A sign of wet MD is a dark blind spot in the middle of the person’s vision.  Often, straight, clear lines appear distorted, blurred, or wavy.  While peripheral vision is typically unaffected by wet MD, people can lose most or all of their central sight.

STAGES OF MACULAR DEGENERATION

Macular degeneration is grouped into three stages of progression – early, intermediate and late MD.

  • Early MD:  In the early stages of macular degeneration, most people do not experience any significant vision loss.  Doctors diagnose early MD by looking for the presence of medium-sized drusen beneath the retina.
  • Intermediate MD: During the intermediate stage of MD, some vision loss is common, but is often not noticeable enough to cause alarm.  In this stage, drusen deposits are large, and the retina often exhibits changes in pigment.
  • Late MD: At this stage of MD, vision loss is noticeable and affects normal, daily function.

CAUSES OF MACULAR DEGENERATION

The exact causes of macular degeneration are unknown, and we need more research to fully understand the disease.  However, the cause of MD is thought to be a combination of both hereditary and environmental factors.

According to the Mayo Clinic, researchers have identified several risk factors for developing MD, including the following:

  • Smoking:  Individuals who smoke double their chances of developing MD later in life;
  • Race:  Caucasians have a higher chance of developing MD than other races;
  • Genetics:  If you have a family history of MD, you are at higher risk of developing the disease;
  • Age:  The risk of MD increases as you age – macular degeneration most often develops in people who are 55 years old or older.

SYMPTOMS OF MACULAR DEGENERATION

The symptoms of macular degeneration revolve around vision.  In dry MD, the light-sensitive retina cells deteriorate, leading to blind spots.  Alternatively, people with MD are more likely to notice wavy and distorted lines and details as fluid leaks into the macula.

The most common symptoms of macular degeneration:

  •  Difficulty recognising faces, words and details;
  • Blurred and distorted vision;
  • Decreased brightness of colours;
  • Reduced central vision;
  • Straight lines appearing wavy or curved;
  • Difficulty adapting to low light;

Typically, dry MD occurs in both eyes.  If only one eye is affected, the patient may not notice any significant vision changes – the good eye will compensate for the affected one.

Available treatments for Macular Degeneration:

  1. Laser Photocoagulation Treatments;
  2. Anti-VEGF Therapy

MEDICAL CANNABIS AS AN ALTERNATIVE TREATMENT FOR MACULAR DEGENERATION

Before exploring the possibility of using medical cannabis as an alternative treatment for macular degeneration, we must first understand how cannabis works:

Cannabis interacts with the body’s natural endocannabinoid system (ECS).  Researchers are still analysing the role of the ECS, but what we have learned so far is astonishing.  According to current research, the endocannabinoid system plays a role in maintaining homeostasis in the body.  It helps regulate a wide range of functions, including metabolism, appetite, immune response, memory, and intercellular communication.

The endocannabinoid system has two different types of receptors – CB1 and CB2.  While CB2 receptors occur throughout the peripheral nervous system and the immune system, CB1 receptors primarily cluster in the brain and spinal cord.  When you consume cannabis, it enters the bloodstream and binds to either CB1 or CB2 receptors.  Cannabis is filled with chemical compounds called cannabinoids.  Researchers have identified at least 85 cannabinoids within cannabis, and each one has a slightly different effect.  The two primary cannabinoids are tetrahydrocannabinol (THC) and cannabidiol (CBD).  Their main difference revolves around with endocannabinoid receptors they bind to – while THC primarily targets CB1 receptors, CBD mainly binds with CB2 receptors.

Because it binds to the receptors in the brain and spinal cord, THC is known as the cannabinoid that causes psychoactive effects.  Alternately, CBD doesn’t affect the brain – primarily targeting the immune system, CBD gives all the therapeutic benefits of cannabis, without the “high”.

Symptoms of macular degeneration

HOW MEDICAL CANNABIS CAN TREAT MACULAR DEGENERATION

Until recently, cannabis has been considered an illegal substance across most of the world.  Historically, it has been difficult to acquire research permits, making the study of cannabis near impossible.  Cannabis research, while not new, is a growing field, and currently, no research has been directly conducted on the effect of cannabis on MD.

However, what we do know about cannabis indicated that it may help manage and reduce the symptoms of macular degeneration. Recent studies have produced promising results – endocannabinoid receptors have been found around the ocular region, and consuming cannabis has been found to reduce inflammation, inhibit vascular endothelial growth factor and lower intraocular pressure.

  1. REDUCING INFLAMMATION

Cannabis is a known anti-inflammatory substance, helping a wide range of inflammatory disorders including arthritis and Crohn’s disease.  However, cannabis doesn’t just target system-wide inflammation – cannabis has shown anti-inflammatory properties specifically for the area around the retina.  This effect is especially seen when the inflammation is connected with diabetes or endotoxin exposure, and both conditions have correlations with Macular Degeneration.  Bacterial endotoxins can often be the instigating cause of macular degeneration, and diabetes is shown to be a risk factor of MD.

CBD, in particular, reduces the body’s production of cytokines, which are pro-inflammatory proteins.  Additionally, the cannabinoid decreases the activation of vital factors in the inflammation response, lowering the activity of primary pathways that help regulate pro-inflammatory genes.

  • INHIBITING VASCULAR ENDOTHELIAL GROWTH FACTOR (VEGF)

Many treatments for MD patients involve injections directly into the eye.  These medications aim to halt the growth of vascular endothelial growth factor.  But, while these treatments often come with harsh side-effects, cannabis has been shown to have the same effect with little to no negative repercussions.  In a 2004 study of brain tumours, researchers found that cannabinoids blocked and inhibited VEGF pathways through the body, showing incredible promise for cannabis as a treatment for macular degeneration.  THC seems to be especially effective at targeting VEGF progression, so for balanced results, a full-spectrum cannabis extract that is THC-rich would be advisable.

  • LOWERING INTRAOCULAR PRESSURE

Medical cannabis has been shown to lower intraocular pressure for patients with glaucoma.  Glaucoma is associated with macular degeneration, and many patients will develop both conditions.  The implications of this research are exciting – while researchers need to conduct further studies, medical cannabis appears to significantly help both eye conditions.  Since ocular endocannabinoid receptors have been discovered, researchers hypothesise that topical application of medical cannabis may be just as effective in reducing pressure around the eye.

  • REDUCING SYMPTOMS OF DEPRESSION

Many people with macular degeneration develop depression as a reaction to learning that they may lose their eyesight.  Older adults are particularly at risk, with studies showing nearly 40% of older adults with MD also suffer from depression.  This is 6% higher than depression rates among individuals with other visual impairments and 24% higher than rates in normally-sighted individuals.  CBD has been shown to have antidepressant qualities and can ease many of the symptoms of depression and anxiety.

While more studies need to be conducted on the effects of macular degeneration, anecdotal evidence suggests that cannabis can profoundly help people who suffer from MD.  As with any medication, cannabis will affect each person differently.  However, from all the research conducted, together with the anecdotal evidence, we can conclude that medical cannabis shows great promise in treating the symptoms of macular degeneration.