Cannabis and Eye Health: Glaucoma Relief, Redness, and Vision Effects

Cannabis products, which interact with the body’s endocannabinoid system, have been researched for their effects on vision and eye comfort. Ethos pharmacist Karen Breitenbach explains the science of cannabis and its influence on the eyes, offering practical advice for those considering it. Understanding how cannabis affects eye health enables informed decisions.

What is glaucoma?

Glaucoma is a group of eye disorders characterized by changes in the optic nerve (or optic disk) associated with loss of visual sensitivity and a reduction in the visual field. Traditionally thought to be due solely to increased intraocular pressure (IOP), but is now recognized to be only one cause of optic nerve damage. Other causes include ischemia (reduced or dysregulated blood flow to the optic nerve), autoimmune reactions, nerve damage, ocular hypertension, and other abnormal physiological processes. Glaucoma is degenerative, first causing a reduction in peripheral vision, and over time, can lead to total blindness.

Can cannabis help with glaucoma?

Inhaled cannabis has been shown to provide short-term (3-4 hours) reduction in intraocular pressure (IOP), which can benefit some patients with elevated IOP. Since the effects are short-term, cannabis has to be dosed from six to eight times per day to achieve consistent pressure reduction. While topical applications, such as eyedrops, show the most promise, they are challenging to formulate because of the highly lipophilic nature of cannabis as well as the physiological and structural barriers of the eye. Ingested cannabis products do not produce the same level of IOP reduction due to the differences in how they are metabolized. Pharmacological treatments for glaucoma, most commonly as eyedrops, are generally longer-acting than cannabis and usually require once or twice daily dosing, making them more practical for long-term management. While cannabis eyedrops are not currently available, there is ongoing research into their formulation and other topical applications for the treatment of glaucoma and other conditions (keratitis and uveitis).

Why does cannabis give me red eyes?

Cannabis causes vasodilation—or the widening of blood vessels—by activating cannabinoid receptors in the eyes. The process that lowers IOP also increases blood flow to eye vessels, resulting in redness. Models indicate that the degree of redness correlates with the dose of THC used.

Can cannabis affect my visual reaction time?

Cannabis may slow visual reaction times, but data suggests reaction times return to baseline within a few hours later after dosing. Impairment is primarily linked with changes in how the brain processes visual information and how the eyes respond to stimuli.

Is consuming cannabis harmful to my eyes?

No long-term studies have assessed cannabis and its effects on vision. Case studies indicate no long-lasting harmful effects, although some data suggest reductions in visual acuity (the ability to see fine details). Data suggest effects resolve after cessation of cannabis use. Cannabis may reduce tear production, potentially leading to dry eyes, so individuals who wear contact lenses or have had certain eye surgeries (such as LASIK) may have increased sensitivity to this side effect.

Can cannabis make my eyes more sensitive to light?

Current data suggests cannabis may increase light sensitivity, with some research indicating a possible improvement in night vision. However, the relationship between cannabis and retinal light sensitivity is complex, and further studies are needed for conclusive data.

Conclusion

Cannabis has multiple effects on the eye, some of which are the subject of ongoing research. While cannabis may offer short-term benefits for certain eye conditions, current evidence suggests that established pharmaceutical treatments are more effective and practical for long-term management. Patients should consult their eye care provider with any concerns about cannabis use and eye health.