Marijuana and the Eyes
Introduction
Since most states are passing more laws to legalize the sale of marijuana for recreational purposes, more questions are being brought to the attention of our optometrists about what it does to our eyes and vision. We see the effects of cannabis because we have cannabinoid receptors all over our body, including the eye.
While there is still much about how marijuana affects the eyes and body we do not know, there are some things we know about the beenfits and detriments to the eyes that everyone should be aware of before partaking.
Glaucoma
Some patients wonder about the potential positive effects of marijuana for glaucoma patients.
Glaucoma is a disease of the optic nerve, which causes a permanent loss of vision. This is generally controlled by decreasing the patient’s eye pressure. It has been an old wive’s tale for many years that marijuana can treat glaucoma, but here are some reasons why marijuana would not work:
While marijuana does decrease pressure in the eyes, it does so for only a relatively short time (30-180 minutes). With glaucoma, the internal pressure needs to be controlled 24 hours every day, which makes marijuana not an ideal treatment for glaucoma. To reduce and maintain eye pressure in a noticeable way, you would have to ingest about 18 to 20 mg of THC six to eight times a day, every day. Ingesting such a large amount of cannabis would dramatically affect your mood, mental clarity, and (if smoked) lung health.
Using enough THC to help reduce the eye’s pressure would also disable your ability to drive, operate machinery, or engage in many daily activities. When studying THC-containing pills and/or cigarettes, within nine months all patients asked to stop due to side effects.
The cost of this amount of marijuana is unaffordable for many patients.
Alcohol also lowers eye pressure for an hour or so after a drink. Yet no doctor would recommend that you drink alcohol every hour to treat glaucoma.
When studying CBD, a derivative of cannabis that does not have mood-altering effects, there is no compelling research that shows CBD to be an effective treatment for glaucoma. In fact, one recent study showed that CBD may actually increase eye pressure, which could make glaucoma worse.
Along with high eye pressure, the optic nerve can also be damaged by low blood flow. This is a problem because marijuana not only lowers eye pressure, but it lowers blood pressure throughout the body. While lowering the blood flow to the optic nerve, it can effectively cancel out the benefit of a lowered eye pressure.
And lastly, the long-term effects from cannabis use are not known, and could possibly damage the eyes or worsen vision in some patients.
Fortunately for glaucoma there are eye drops and surgical procedures that can usually lower the eye pressure with more accuracy, consistency, and less side effects.
Until more research is done, the American Academy of Optometry, the American Optometric Association, the American Glaucoma Society, and the American Academy of Ophthalmology do not recommend marijuana or other cannabis products for the treatment of glaucoma.
Red Eyes
The appearance of red eyes after having smoked cannabis is without a doubt the most visible and most well-known effect of the plant on ocular health. THC (tetrahydrocannabinol) in marijuana lowers blood pressure which dilates the blood vessels and increases blood flow throughout the body. This causes the blood vessels in the eyes to expand, causing redness or bloodshot eyes. Although it is alarming, this effect has no consequence on the health of your eyes. Selecting a strain with more CBD and less THC will lessen the redness, but also reduce the “high.”
Dry Eyes and Meibomian Gland Dysfunction (MGD)
Marijuana causes a decrease in tear production and reduces the blink rate, making the eyes feel dry. Decreased blinking then causes MGD, even furthering the symptoms of dryness. These symptoms can be uncomfortable for those who wear contact lenses or who have had laser refractive surgery, such as PRK and Lasik. This vasodilation also affects the salivary glands causing a dry mouth.
Visual Acuity
A 2021 research concludes that cannabis has significant adverse effects on certain visual functions, including:
Visual Acuity, which is the ability to identify shapes and details
Contrast Sensitivity
Nighttime Vision
Slowing Down the Image Processing By The Retina
Another effect of cannabis on vision is to slow down the brain’s treatment of images and information. Under the influence, spatial perception is altered, and eye-hand reflexes slow down. That is why it is more cautious to consume cannabis in a secure context that is favorable to relaxation. One should never take the wheel under the influence of cannabis, especially because of the deficit in ocular movements it provokes, especially when the eye scans the horizon to find its bearings.
A 2017 study compared the retinal function of people who used cannabis with those who did not. Researchers found a delayed response time for cannabis users, which may impair the eyesight of people who use cannabis regularly.
Eye Fatigue
Cannabis can modify ocular movements and tire out the eyes, which sometimes complicates reading small characters on a screen or even the ability to understand the information one reads.
Dazzlement and Imbalance of Near and Far Vision
More rarely, the pupil dilation provoked by cannabis can create dazzlements and imbalances between near vision and far vision. People who wear multifocal contact lenses can therefore suffer a diminution of their peripheral vision after having consumed cannabis.
Macular Degeneration
A 2022 review of studies recognizes CBD for its antioxidant and anti-inflammatory properties, which could make it a potential aid in treating macular degeneration.
Another 2022 study suggests that cannabis could accelerate the loss of blood vessels due to its anti-angiogenic properties. Therefore, using cannabis could cause macular degeneration to develop sooner in younger people because it speeds up blood vessel loss. Also, cannabis smoke, like tobacco smoke, contains a similar amount of carcinogenic and toxic compounds that may damage the eye’s blood vessels.
For these reasons, CBD is not recommended at this time as a formal line of treatment for macular degeneration, but it may be useful for other conditions, such as pain management.
Summary
More studies must be conducted to better understand the effects of cannabis on the anatomy of our eyes and vision, especially whether these effects of cannabis affect long-term eye health and vision. While we wait for those studies, simply be careful and cautious while consuming!
The Bottom Line About Marijuana and the Eyes
Marijuana does have many benefits that should not be overlooked. Yet the benefits for the eyes are not great.
The largest association of eye physicians and surgeons in the world does not endorse cannabis or its derivatives as a treatment for any eye disease, including glaucoma.
Do not self-medicate with marijuana in an attempt to treat an eye disease. You can lose your vision if you do not have a reliable, effective treatment.
Speak with our optometrists if you have any questions or need to find a treatment option that is best for you.
Tell your optometrist if you do use marijuana regularly. Be honest. We are not here to judge anyone.
Like everything else in life, please use marijuana responsibly.
