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How does marijuana affect vision?

Health experts agree that smoking marijuana can damage the lungs. The deleterious effect of chronic, frequent use of marijuana upon the brain is also well established. However, while more research is required regarding the potential beneficial and/or detrimental effects of marijuana on vision, we do know that the drug has a few key effects on the eyes.

One of the most noticeable effects occurs shortly after smoking the drug: red eyes. 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.

Researchers are still examining the potential negative impact of marijuana on peripheral vision, changing eye pressure, and visual processing. Using marijuana may have potentially serious impacts on these areas.

Some people wonder about the potential positive effects of the marijuana for glaucoma patients. Glaucoma is a disease of the optic nerve and patients with glaucoma have increased eye pressure. While marijuana does decrease pressure in the eyes, it does so for a relatively short time. Since marijuana also usually impacts people’s ability to concentrate, make decisions, drive, operate heavy machinery, etc., the drug is not currently a recommended treatment for the disease. 

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