Here’s Why You Might Experience Blurry Vision After Smoking Cannabis

close up of man's eye showing people get blurry vision after smoking cannabis

Entering a room full of stoners puffing on a cannabis peace pipe is sure to lead to some smoky eye, but what about cannabis causing blurred vision? Many people have experienced blurry vision after smoking cannabis, which leads one to wonder; does hitting the bong lead to blurred vision? It can, and here’s why.

Studies on Blurry Vision After Smoking Cannabis

man passing a joint for smoking cannabis

A study conducted in France found that cannabis slows the response of retinal cells to electrical signals being transmitted to the brain. The delay temporarily causes blurry vision after smoking cannabis as the signals travel to the visual cortex. Dr. Vincent Laprevote of the Pole Hospitalo-Universitaire de Psychiatrie du Grand Nancy was the head researcher of the study and wrote about the study in the Journal of American Medical Association for Ophthalmology.

Researchers studied 28 people who were regular cannabis users for the study along with 24 people who were not cannabis users. Cannabis users registered a response time of 98.6 milliseconds while non-cannabis users registered a response time of 88.4 milliseconds.

Laprevote noted that the delay is short but significant. "This finding provides evidence for a delay of approximately 10 milliseconds in the transmission of action potentials evoked by the retinal ganglion cells." Researchers believe that the study provides evidence of how cannabis affects the central nervous system and retinal processing.

More research needs to be conducted to fully understand exactly how cannabis affects vision, according to Laprevote. The doctor says that research is important for public health awareness as the legalization debate continues without the facts.

"Independent of debates about its legalization, it is necessary to gain more knowledge about the different effects of cannabis so that the public can be informed." Researchers say that driving, working and other activities are affected by the vision delay.

Laprevote went on to say that conducting further research would provide more knowledge of the potential consequences associated with cannabis and retinal dysfunctions. He also noted that more research was needed to determine if the retinal dysfunction is permanent or if they disappear after cannabis use ends.

Possible Study Issues

medical marijuana bud laying of medical marijuana bud

The French Interministerial Mission for Combating Drugs and Addictive Behavior provided the grant for the study, and other researchers pointed out that the study neglected to account for the dosages used for cannabis users as well as the purity of cannabis that the subjects used.

Dr. Christopher Lyons is an ophthalmologist at the University of British Columbia and Anthony G. Robson is an electrophysiologist at London's Moorfields Eye Hospital. Both researchers concede that the study is important to understand the potentially toxic effects of cannabis. However, the lack of dosage information along with the number of subjects used for the study proved problematic.

Leprevote, Lyons, and Robson all concluded that more research is needed and that the results of study are just preliminary.

Does Cannabis Improve Vision?

beautiful shot of woman's eyes

While the French study shows that cannabis may temporarily delay clear vision, rumor has it that cannabis may actually improve vision, so does cannabis improve vision or not? According to Jamaican fishermen and tadpoles, a little ganja can improve your night vision.

A team of researchers at the Montreal Neurological Institute and Hospital found that chemicals in cannabis improved low-light vision of tadpoles. Researchers were surprised to find that cannabis increased the activity the retinal ganglion cells of tadpoles.

Scientists used increased levels of cannabinoids on tadpoles for the research and Professor Ed Ruthazer says that he did not believe his own eyes at first while conducting the tadpole study.

"Initially you distrust yourself when you see something that goes against widely held ideas, but we tried the experiment so many times, using diverse techniques, and it was a consistent result," he said. "It was such a strong effect, we knew there was something important here," concluded Ruthazer.

The scientists found that CB1 receptors suppress the amount of chloride transported into the retinal ganglion cells. Chloride levels decrease as the receptor is activated and hyperpolarizes the cell and enabling stimulation. In a nutshell, increased levels of cannabinoids led to the tadpole's ability to see better at night.

Does It Apply to Humans?

cannabis plant in high def

Whether or not the same is true for people is up for debate, however, the tadpole study was prompted by evidence of fishermen in Jamaica and Morocco who used cannabis for improving night vision before fishing.

A pharmacologist in Jamaica wrote that the local fishermen were able to see better after consuming weed. M. E. West wrote that the fishermen who smoked cannabis or drank a rum made with cannabis stems and leaves could navigate without a compass due to their "uncanny ability to see in the dark."

West wrote that it seemed impossible that fishermen could find their way around coral reefs without a compass in the dark and was convinced that the fisherman he accompanied over two-decades ago had far better night vision because of cannabis. The fishermen told West about Moroccan fishermen who also had excellent night vision, which prompted a 2002 study.

Fishermen, as well as Moroccan mountain dwellers, experience improved night vision after smoking hashish, according to the studies. Research conducted during the 2002 study in the Moroccan Rif mountains found that cannabis did indeed improve the night vision in all research subjects.

The research subjects smoked cannabis sativa blended with tobacco, a concoction the locals call "Kif," and researcher used a device from LKC Technologies called a scotopic sensitivity tester to measure retina function of the mountain dwellers.

More Research is Needed

doctor checking eye health, checking about blurry vision after smoking cannabis

One thing that all researchers agree on is that more research is needed on the effect of cannabis on vision. Dr. Raj Maturi is an ophthalmologist at the Indiana University School of Medicine and says that the long-term effects of cannabis on eyesight are unknown.

"Marijuana might help some aspects of vision in the short term, but it might be harmful if used chronically. These findings suggest we need longer-term studies of the effects of chronic marijuana use on vision."

Maturi added that cannabis is effective in treating the symptoms of conditions like glaucoma by lowering pressure in the eye and providing pain relief, but that the brain and nervous system are also affected.

Glaucoma is a disease that can lead to blindness and damages the optic nerve with fluid building up in the front part of the eye, creating pressure. Glaucoma is the leading cause of blindness for people over 60. Cannabis can temporarily decrease this buildup and therefore relieves eye pressure and relieves pain.

The National Academy of Sciences also says that cannabis can improve vision for glaucoma patients for several hours but also notes that the effects are only temporary and therefore does not recommend cannabis as a treatment option for glaucoma.

Based on the few scientific studies available on the effects of cannabis on vision, it would appear that cannabis can have both negative and positive impacts on eyesight. People may experience blurred vision after smoking cannabis but may also have better night vision.

While you might experience a few seconds of blurry vision after smoking cannabis, if you smoke at nighttime and get the munchies, at least you'll be able find your way to the kitchen fridge in the dark, or to climb every mountain.