The effect of the cannabinoid CBD on glaucoma has been studied for a long time. Eye pressure disease, even causing permanent blindness, is an unfortunate, incurable disease in humans, which fortunately progresses slowly in most cases. In this article, we will get to know glaucoma as a disease, the endocannabinoid system behind it, and also whether CBD oil could be helpful in lowering eye pressure or other factors behind the disease.
What is glaucoma?
Glaucoma, i.e. intraocular pressure or cataract, is a disease affecting the optic nerve, which is the most common cause behind permanent visual impairment. In Finland, it affects just under 100,000 people, and it is more common only in people over 65. However, approx. 1% of people aged 40+ have glaucoma, often without knowing it. The risk of getting sick increases with age, but the disease is also sometimes found in children and young people. (1)
The cause of eye pressure is not known, but the eye pressure is usually elevated for a long time before the onset of the disease. The increase in pressure causes metabolic and blood circulation disturbances in the optic nerve, which eventually damages the optic nerve. Pressure on nerve fibers also affects the onset of the disease. (1)
Glaucoma in children always has a clear cause behind it, such as eye damage or an inflammatory disease . (2)
Glaucoma symptoms
Glaucoma is usually asymptomatic until the disease is already too advanced to stop it. The first symptoms are observations that you cannot see properly with the other eye. As the disease progresses, vision deteriorates in areas of both eyes, sometimes faster in one than the other. Glaucoma is also associated with tube vision, i.e. a condition where the field of vision has shrunk to a small tube in the middle of the field of vision. (1)
A sudden attack of intraocular pressure (acute angle-closure glaucoma) is accompanied by strong symptoms. The eye pressure suddenly rises dangerously high and then the symptoms are a severe headache and pain in the eye area, redness of the eye and reduced vision in the affected eye. Sometimes the seizure is not triggered by medication, but it is necessary to open the corner of the eye with the help of a laser. (1)
The first symptoms of glaucoma are usually a loss of vision in one eye. As the disease progresses, the vision usually deteriorates in areas of both eyes.
Prevention of intraocular pressure
Ocular pressure is partly hereditary and myopia may also contribute to its occurrence. There is not much that can be done to prevent it, but you can and should take the best possible care of eye health in general.
Some factors may have an effect on the development of glaucoma. For example, activities that put pressure on the head, such as weight lifting, high blood pressure, stress and even playing fans may make it possible for the intraocular pressure to rise permanently, but these have not actually been classified as risk factors, and they do not directly lead to the onset of glaucoma.
Glaucoma diagnosis and treatment
Most of the time, the eye pressure is elevated if there is reason to suspect glaucoma, but this is not always the case. Eye pressures can be at a normal level and therefore just measuring the eye pressure is not enough to confirm the diagnosis. Usually, studies use a combination of several methods, which take into account intraocular pressure, visual field, nerve pressure layer and the chamber angle of the eye. (1)
Glaucoma is treated both with eye drops that equalize the eye pressure and with drugs taken internally that affect the pressure. Keeping the pressure as low as possible is its most important treatment method. Treatment of the ventricular angle with laser and pressure surgeries are also used alongside medical treatment. (3)
Glaucoma cannot be completely cured, but medications slow down the progression and alleviate the symptoms. Glaucoma usually progresses slowly, and in almost all cases it does not lead to complete blindness.
Endocannabinoid system underlying glaucoma
The endocannabinoid system balances all body functions. Its most important task is to maintain and ensure the functionality of vital functions. The endocannabinoid system consists of the body’s endogenous cannabinoids (endocannabinoids), their corresponding cannabinoid receptors (CB1 and CB2), and their decomposers.
The body’s endogenous cannabinoids have numerous important functions in the eye area, and both of them have been observed in the eye area, excluding the lens (4). Endocannabinoid in glaucoma with anandamide (AEA) has a role e.g. in keeping intraocular pressure steady and low. The functions of arachidonylglycerol (2AG) in glaucoma are not yet completely clear, but they are related to anti-inflammatory and neuroprotective effects (4).
Cannabinoid receptors are also found throughout the eye area. On the retina, their activation improves e.g. nerve flexibility. The background of glaucoma seems to be influenced especially by the CB1 receptor, which has been widely observed throughout the entire eye area. (5)
Does CBD help glaucoma symptoms?
CBD is a well-known and researched compound called cannabinoid found in hemp, which naturally has several therapeutic effects. CBD oil may not directly affect eye pressure by lowering it, but its certain properties may slow down the progression of glaucoma.
At first it was thought that cannabinoids, both endo- and exocannabinoids, would affect the eye and intraocular pressure via the central nervous system. Studies have since shown that cannabinoids act locally through the direct mediation of receptors (5). CBD does not work through the known cannabinoid receptors CB1 and CB2, but through other receptors in the body such as e.g. through the serotonin receptor.
The effect of CBD is transmitted through body receptors
Endocannabinoids respond to the endocannabinoid system’s own receptors, but they also have other receptors in the body through which they act. Listed below are a few receptors outside of the endocannabinoid system that have some role in glaucoma.
5-HT1A, a member of the serotonin receptor family, has been found in animal experiments to be a pathway that alleviates keratitis, through which CBD can influence. (6,7)
The GRP18 receptor is a newly identified and even suspected cannabinoid receptor, which has been widely observed e.g. in eye tissues and retina. CBD might have an eye pressure-lowering effect through the GPR18 receptor (6). GRP18 is also activated by anandamide (4).
GPR55, assumed to be the third cannabinoid receptor, is activated by both phyto-, endo- and synthetic cannabinoids. CBD also acts through this receptor and it has been found that this connection would have an inhibitory effect on the growth of the growth cone of the eye. (6,7)
TRPV channels are relevant channels in the CBDin the background of the effect of , both in the eyes and in the body. In the eyes, they are at least involved in the background of the anti-inflammatory properties. (6,7)
CBD protects the nervous system and reduces inflammation
CBD has been found to have nervous-protective and calming properties. Glaucoma is caused by nerve damage, the calming of which could reduce the strain on the optic nerve and nerve fibers (7). Antioxidative and anti-inflammatory, i.e. anti- inflammatory, effects are also behind the eye health-related healing properties.
CBD is best absorbed through the skin
It is often recommended to dose CBD through the skin, because it is quickly absorbed directly into the bloodstream and travels quickly throughout the body.
In relation to eye pressure, in order to get the best results, it has been thought that CBD should be dosed locally through the skin, as the absorption is not optimal when taken orally. It seems that not enough CBD reaches the eye to easily detect a drop in eye pressure. Another challenge associated with lowering intraocular pressure with CBD is that CBD has such a short duration of action that it should be dosed practically all the time. (6,7)
You can read more about the transdermal effect of CBD here .
Ocular pressure can also occur in cats, dogs and other animals.
Glaucoma in cats and dogs
Eye pressure also occurs in animals. Glaucoma in cats and dogs is similar to that in humans; it is accompanied by visual impairment and possible blindness. Glaucoma in animals is also treated with drugs and, in extreme cases, with surgery. Interestingly, cat glaucoma usually gets better, but dog glaucoma does not. Glaucoma in animals can be difficult to detect at first, and they have the same challenge as humans, i.e. it is often diagnosed too late. Regular eye examinations for animals are also important, so that possible diseases, including glaucoma, are noticed in time. (8,9)
In summary
Glaucoma is a common sight-damaging disease that unfortunately is often diagnosed only when the disease has already progressed far. It is initially asymptomatic and as a slowly progressing disease does not initially cause such a great harm to life that it would be investigated. CBD has been found to affect e.g. the properties that protect the nervous system and affect glaucoma mainly come from them and the properties that reduce inflammation.
Sources
- Seppänen M.. 2021. Health Library Duodecim. Eye pressure (glaucoma). https://www.terveyskirjasto.fi/dlk00452. Referred on 5/11/2022.
- Vaajanen A., Gielen F. and Tuulonen A.. 2017. Period book Duodecim. Glaucoma and alternative treatments. https://www.duodecimlehti.fi/duo13857. Referred on 5/11/2022.
- Rotten. M.. 2018. Period book Duodecim. Glaucoma treatment – fine art between efficacy and adverse effects. https://www.duodecimlehti.fi/duo14506. Referred on 5/11/2022.
- Cairns EA, Baldridge WH and Kelly MEM. 2016. Neural Plast. The Endocannabinoid System as a Therapeutic Target in Glaucoma. https://pubmed.ncbi.nlm.nih.gov/26881140/. Referred on 5/11/2022.
- Tomida I., Pertwee RG and Azuara-Blanco A.. 2004. Cannabinoids and glaucoma. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1772142/. Referred on 5/11/2022.
- Aebersold A., Duff M., Sloan L. and Song ZH.. International journal of experimental cellular physiology, Biochemistry and pharmacology. Cannabidiol Signaling in the Eye and Its Potential as an Ocular Therapeutic Agent. https://www.cellphysiolbiochem.com/Articles/000371/. Referred on 5/11/2022.
- Passani A., Posarelli C., Sframeli A., Percipalli L., Pellegrini M., Guidi G and Figus M.. 2020. Journal of medicine. Cannabinoids in Glaucoma Patients: The Never-Ending Story. https://www.mdpi.com/2077-0383/9/12/3978/htm. Referred on 5/11/2022.
- Evidence. 2019. Glaucoma or eye pressure disease in dogs. https://evidensia.fi/hoitovinkit/glaukooma-eli-silmanpainetauti/. Referred on 5/11/2022
- Bauhaus JM 2018. Hill’s Pet. Cat Eye Care: Identifying and Preventing Six Common Cat Eye Problems. https://www.hillspet.fi/cat-care/healthcare/common-cat-eye-problems. Referred on 5/11/2022
