New studies seem to indicate that cannabinoids stimulate CB1 receptors in the brain to increase vision, including at night.
It has long been known that use of cannabis positively affects eye function. Some of the first modern medical activists for reform included those with glaucoma – a condition that causes damage to the optic nerve. Evidence also now seems to suggest that cannabis also may positively affect the night vision of those who use it – with implications that cannabinoids may improve overall visual acuity.
One of the earliest studies on the same came out of the University of the West Indies. A pharmacologist noted that fishermen who either smoked cannabis or drank rum infused with leaves of the plant had "an uncanny ability to see in the dark". Researchers in Morocco using a scotopic sensitivity tester – a machine that tests for the development of glaucoma, also found that both synthetic and natural THC seemed to improve the night vision of their test subjects.
Recently, another study provides even more evidence that cannabis can actually improve night vision. The findings, published in the journal eLife, are potentially a breakthrough in how cannabis might be used to treat a range of patients with degenerative eye diseases.
It has been common knowledge since the discovery of the endocannabinoid system, that marijuana works by stimulating both CB1 and CB2 receptors found throughout the body. CB1 receptors are primarily found in the brain and nervous system.
However, what is interesting about this latest study is that it seems to fundamentally refute earlier hypotheses about why cannabis acts the way it does to improve vision overall – not just at night or in low light situations. Investigators in the West Indies hypothesized that cannabis, since its use dilated the pupils, it also allowed more light to fall on the retina. Researchers also theorized, that stimulation of the CB1 receptor, which is found deeper in the head, than the visual cortex, might be responsible for such improvements. This new study seems to quantify this second theory. By applying cannabinoids to the eye tissue of African toads, researchers found, that cannabis appears to stimulate the actions of retinal ganglion cells – making them more sensitive to light by inhibiting a protein called NKCC1 via the CB1 receptor.
NKCC1 is a transporter protein that moves sodium, potassium and chloride ions in and out of cells and in doing so, determines the electrical properties of nerve cells.
What these latest studies seem to indicate, is that cannabinoids make such cells more "excitable" and therefore more sensitive to light.
It has been known for quite some time, that use of cannabis can significantly slow down the progression of eye conditions leading to blindness and has overall neuroprotective effects. Researchers at the University of Spain conducted tests on rats with retinitis pigmentosa (a degenerative eye disease). After 90 days, the rats who were treated with cannabinoids had better results in vision tests and actually acquired 40% more photoreceptors than the rats that had not been treated with the drug. This is in line with other research that also confirms that cannabis actually causes cell growth in the brain – a process called neurogenesis.
Researchers at the University of Waterloo in Ontario also found evidence, that babies exposed to cannabis in the womb also seem to have better vision – specifically in their ability to track moving objects. Research showed, that exposure to marijuana in the womb improved global motion perception – a processing function within the brain's dorsal visual pathway. The children who were studied were all born to mothers who had used nicotine, other drugs like methylamphetamine or alcohol during pregnancy. In direct contrast, fetuses exposed to alcohol showed a negative effect, while nicotine and methamphetamine seemed to have no effect. Despite this of course, scientists in this study were quick to warn, that marijuana does not have an overall positive effect on prenatal development.
What the research clearly does indicate, no matter how inconclusive at this point, is that cannabis seems to improve vision in several different ways by stimulating the CB1 receptor. This effect has been noticed by both those with eye diseases and those without. As a result, the promise of cannabis for treating a large range of eye diseases seems highly promising.
THC acts within the brain to enhance the natural stimulation of vision in low light situations created by a naturally occurring endocannabinoid within the body called anandamide – the so-called "bliss molecule" also responsible for creating the "runner's high".
THC also seems to protect the inner layers of the retina. This is consistent with other findings, that show that using THC seems to help protect against both brain trauma and carbon monoxide poisoning.
A 2014 study showed that those with residual THC in their system were 80% less likely to die from traumatic brain injury. UCLA researchers reviewed data on 446 adults treated in Torrance, California for TBI. All were first tested for THC. Those who tested positive for the drug were about 80% less likely to die compared to those without THC in their systems.
What this research also confirms is the importance of the endocannabinoid system (ECS) in maintaining homeostasis – or the optimal balance in the body, particularly in changing circumstances. Endocannabinoids produced naturally by the body act as messengers, that either speed up or slow down processes in the body necessary for optimal functioning. Dysregulation of the ECS is thought to contribute to a number of diseases and conditions, from cancer to fibromyalgia.
The ECS theory of disease, which came out of the discovery of the endocannabinoid system itself, holds that when the body does not produce enough endocannabinoids on its own or cannot regulate them properly, the human body becomes more susceptible to conditions or illnesses like cancer, inflammatory diseases and vision loss.
The body creates endocannabinoids with the help of fatty acids – in particular omega-3 fatty acids.