Could Regular Pot Smoking Harm Vision?
Study suggests that it might slow signaling among cells that deliver visual information to the brain
THURSDAY, Dec. 8, 2016 (HealthDay News) — Smoking pot regularly may be linked to a limited degree of vision impairment, a new French study suggests.
The finding stems from very preliminary research involving just 52 participants, 28 of whom were regular marijuana users. That meant they used marijuana at least seven times a week.
The question posed in the study: Does marijuana affect the healthy functioning of retinal ganglion cells (RGCs), which are situated on the surface of the retina? These cells receive incoming visual information, and are considered the first link in the pathway that connects the retina to the part of the brain where eyesight is processed.
The answer: Regular pot users do appear to experience a slight delay in their RGC signaling. And that could indicate impaired vision, the study authors said.
Still, experts stressed that the findings remain preliminary and people shouldn’t be overly alarmed by the findings.
And, according to study author Dr. Vincent Laprevote, his team now have to “measure if this delay is permanent, or recedes with cannabis cessation.” Laprevote is a hospital practitioner at the Pole Hospitalo-Universitaire de Psychiatrie du Grand Nancy in Laxou, France.
His team noted that marijuana has long been known to have an impact on nervous system communications.
To explore the possibility that this might include vision function, the French scientists conducted neural signaling tests to compare RGC function between regular pot smokers and nonsmokers.
Those tests determined that regular pot users experienced a 10-millisecond delay in the speed with which their RGCs sent key signals to the brain via the optic nerve.
The findings were published online Dec. 8 in the journal JAMA Ophthalmology.
Although the result could signal the potential for vision trouble, the team noted that it did not necessarily prove that regular smokers do actually experience vision impairment. The association seen in the study also did not prove that pot use actually caused the delay in RGC signaling, the researchers said.
Laprevote also pointed out that most of the participants did not complain of any vision issues before the study began. He suggested, however, that smokers might be experiencing vision trouble without being consciously aware of it.
Dr. Christopher Lyons co-authored an editorial that accompanied the study. He said that “the evidence [in the study] for decreased retinal function is weak for several reasons.”
Lyons pointed to the extremely small pool of patients, as well as the lack of visual impairment symptoms prior to the study, and a lack of clarity on additional lifestyle factors that could have affected the results, such as diet and cigarette smoking history.
Lyons, who is a professor in the department of ophthalmology and visual sciences at the University of British Columbia in Vancouver, still described the research as “timely,” given the increasing trend towards legalization of marijuana in the United States, for both medical and recreational use.
Also, medical marijuana has been promoted as an alternative treatment for the vision-robbing condition glaucoma, because research has shown it can lower blood pressure in the optic nerve for short periods of time. However, the American Academy of Ophthalmology does not recommend medical marijuana for glaucoma patients.
Lyons suggested that “further, more robust studies are needed to test whether long-term use of cannabis has any effect on retinal or optic nerve function.”
But Paul Armentano, deputy director of NORML, the nonprofit marijuana advocacy organization, argued that “it remains unclear at this time whether or not these findings possess any real-world significance.”
Armentano said, “Given the reality that tens of millions of people consume cannabis regularly, and that people around the world have been consuming cannabis for generations, one would presume that any potential adverse effects on vision would have been previously documented. Or that they are, at worst, nominal to the overwhelming majority of those who consume the substance.”
Study suggests that it might slow signaling among cells that deliver visual information to the brain
Red, bloodshot eyes have always been a tell-tale sign of marijuana consumption—a temporary phenomenon that’s due to the effects of cannabis on blood pressure. But cannabis can also affect the eyes in other ways. Now, some research suggests that the neuroprotective and antioxidant properties of marijuana compounds cannabidiol (CBD) and tetrahydrocannabinol (THC) may be able to support vision and offer some protection against common diseases of the eye and optic nerve.
Cannabis & the Eyes: A Complicated Relationship
Relatively little research has been done on how—or whether—cannabis can affect vision, prevent any of the common eye diseases or relieve symptoms of those diseases. While some studies propose that cannabis has clear benefits for eye health, others claim the opposite, that cannabis can actually harm vision and the pathways for processing visual information in the brain. Complicating that picture are the many accounts by cannabis consumers themselves, who say that cannabis makes vision sharper and reduces the symptoms of glaucoma, a common eye disease.
The effects of cannabis on the eyes and the overall visual system come from the interaction of a number of factors, including the unique responses of a person’s endocannabinoid system (ECS) and the type of cannabis they use. All these things can affect the various parts of the visual system, including the tissues of the eye itself, the optic nerve, and the neural pathways in the brain that process and store visual information.
The ECS is a vast network of receptors found in tissues and organs throughout the body. These receptors are activated both by cannabinoids produced by the body itself and by the very similar ones found in cannabis, which is why consuming cannabis has such a diverse range of health benefits. The tissues of the eye contain large numbers of the most common cannabinoid receptor, CB1, and so do many areas of the brain. This means that consuming cannabis in any form can trigger responses in various parts of that visual system—but those responses can be highly variable.
New Research Suggests Marijuana May Improve Vision
The first studies on how cannabis affects vision seemed to demonstrate that those effects were either non-existent or negative. This research proposed that cannabis causes a delay in the processing of visual information in the brain, so that there could be a lag time between seeing something and taking action in response to it, such as making decisions while driving, moving or picking up objects. Other research based on interviewing cannabis consumers about their vision revealed that some people felt that they saw better while taking cannabis, others felt their vision was worse, and some didn’t report any change at all.
But those differences could be explained by factors including the kind of cannabis a person used, how often they used it and under what circumstances—and even the amount of CB1 receptors an individual has in given areas of the body. What’s more, the activity of those receptors can be affected by numerous factors such as the number of natural cannabinoids in a person’s system or other health conditions that affect the ECS in general. Those variations mean that cannabis can have a range of different effects on different people.
Now, though, recent research that takes into account new discoveries about the ECS reveals a different and far more positive picture. The action of cannabinoids on CB1 receptors in the eye, particularly the retina, seems to increase visual sensitivity in low light and may also increase visual contrast—the ability to pick out things from their background. Though the research involved tadpoles, not humans, these insights could have implications for people whose work requires good night vision, or for those who have problems with distinguishing between things of similar color or brightness.
Cannabis May Treat Glaucoma
Cannabis has also shown promise in treating glaucoma—a serious eye disorder in which intraocular pressure is too high. This can cause fluid to build up inside the eye, which can damage the optic nerve and lead to blindness. The conventional treatment for glaucoma is medicated eye drops, which work to bring intraocular pressure down to normal levels. But some glaucoma patients and eye specialists report that cannabis can also help reduce intraocular pressure and help preserve eyesight.
This is because cannabis, particularly THC, lowers blood pressure—the same effect that’s responsible for the famous red eyes that accompany cannabis use. Cannabis relaxes and dilates blood vessels, allowing more blood to flow. And in the eye, it appears to have the same pressure-reducing effects.
But ophthalmologists and other vision specialists have been reluctant to embrace marijuana as a treatment for glaucoma. They say that its effects are only temporary and that cannabis has too many other effects on the brain and the rest of the body for them to recommend it.
Marijuana & Other Eye Diseases
Research on the impact of cannabis on eye health has been limited and that includes studies about whether cannabis can affect other common eye problems such as cataracts and macular degeneration, a condition that tends to affect older adults.
But marijuana has documented effects as a neuroprotectant, capable of supporting the health of nerves and the neurons that transmit information within the brain. This means it may also be able protect the optic nerve in general.
Cannabis, especially strains high in CBD also have potent antioxidant and anti-inflammatory properties. This allows cannabis to help protect cells from oxidative stress and other processes that contribute to their breakdown and death.
These properties may mean that cannabis can increase the rate of cell survival in the eyes and support the overall health of eye tissues. In this way, cannabis helps to protect the eyes against factors that contribute to the development of cataracts or macular degeneration, as well as less-common kinds of retinopathies.
Many conditions can affect the eyes as well as the entire visual processing system. But because this system is rich in ECS receptors, the well-known properties of cannabis as a neuroprotectant and antioxidant may have an important role to play in keeping eyes healthy for life.
If you’re new to cannabis and want to learn more, take a look at our Cannabis 101 post. HelloMD can help you get your medical marijuana recommendation; it’s easy, private and 100% online.
- Health Conditions
Your trusted source for cannabis information.
Red, bloodshot eyes have always been a common sign of marijuana consumption. But cannabis can affect the eyes in other ways. Some research suggests the neuroprotective and antioxidant properties of CBD and THC may support vision and offer some protection against common eye diseases like glaucoma.