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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.

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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.

Smoking Weed Regularly May Cause Vision Problems

New research suggests that weed could mess up your vision beyond just bloodshot eyes.

Published in JAMA Ophthalmology this week, a 52-person study explores how pot might influence the function of the user’s retinal ganglion cells, or the nerve cells just behind the surface of the retina that transmit information back to the brain to create a visual image.

“We showed an association between regular cannabis use and a delay in the visual processing,” researcher Vincent Laprévote, M.D., Ph.D., from the Pole Hospitalo-Universitaire de Psychiatrie du Grand Nancy, Laxou, France, told Motherboard. “Our hypothesis is that regular cannabis use could slow down the transmission between retinal neural cells.”

The researchers found a delay in the transmission of action potentials, or neural signals, from the retina back to the brain—a result which ultimately could lead to a change in vision. Laprévote said it’s a long-term effect, since participants had to stop their consumption before the tests. On average, they’d been using cannabis for six years. Whether this effect has behavioral consequences, the researchers have yet to find out, he said.

“Our findings may be important from a public health perspective since they could highlight the neurotoxic effects of cannabis use on the central nervous system as a result of how it affects retinal processing,” the researchers wrote. Overall, this might indicate brain neurotransmission abnormalities in cannabis users.

To conduct their study, Laprévote and his colleagues used a standard electrophysiological measurement known as “pattern electroretinography (PERG).” An electroretinogram is a test that evaluates electrical activity among neural and non-neuronal retinal cells in response to light.

Of the study’s participants, 28 used cannabis regularly, while the other 24 functioned as controls. The researchers found that the pattern electroretinography took longer in regular cannabis users: a median of 98.6 milliseconds, as compared with 88.4 milliseconds for the controls.

With that said, though cannabis use may cause red eye upon getting stoned, it’s been proven helpful with eye issues like glaucoma, and to even make regular users better drivers than otherwise—which of course entails proper vision. Among glaucoma patients, cannabis helps alleviate the pressure they feel in their eyes, which otherwise causes damage to the optic nerve and potential vision loss.

So whatever the overall implications may be in regard to this study and cannabis’ effects on vision, as legalization sweeps the country, it’s important to conduct more research to get to the bottom of how smoking pot influences eyesight.

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