There are a number of eye diseases in animals that can be challenging to manage and, if not successfully treated, can result in chronic pain and/or loss of vision. These include a wide variety of conditions including corneal disease, uveitis, glaucoma, as well as diseases of the retina and/or optic nerve. With the growing interest in the use of cannabinoids for treating a variety of medical conditions (e.g. epilepsy, osteoarthritis, neuropathic pain, etc.) many have also wondered about the possible benefit of using cannabis-derived products for treating ocular disease in pets.

Cannabis has been used medically in humans for years. The two most commonly used cannabinoids are Δ9-tetrahydrocannabidiol (THC) and cannabidiol (CBD). THC is toxic in pets and only CBD products containing less than 0.3% THC (dry weight) can be used in our companion animals. CBD can be extracted from the cannabis plant but can also be produced synthetically in the laboratory setting; In recent years, many CBD products have made their way into the commercial marketplace.

There are many cannabinoid receptors located in tissues throughout the body and modulating these receptors can have beneficial effects including anti-inflammatory, antioxidant, and neuroprotective effects. The most common cannabinoid receptors found in ocular tissues include:

- Cannabinoid receptor type 1 and 2 (CB₁R and CB₂R)

- G protein-coupled receptor (GRP)

- Transient receptor potential vanilloid-1 (TRPV1)

- Serotonin 5HT_1A receptors (Serotonin 5HT_1A)

While there are a number of scientific studies and a growing body of evidence to support the use of CBD for treating a variety of diseases, the research that has been done to date - exploring the possible benefits of cannabidiol for treating ocular disease in animals - is limited.

A review of the body of evidence (peer-reviewed, published data) into the use of CBD products for treating ocular diseases – specifically in dogs – was conducted and published in 2024^[1]. They found that very few controlled clinical trials had been conducted to date and that there is insufficient evidence to recommend CBD products as a standard or conventional therapy for treating any eye disease in dogs. Key findings and limitations reported include the following:

• CBD, after given systemically, was detectable in canine tears but had no significant effect on intraocular pressure (IOP) or on tear production (STT).
• Topical administration of CBD is challenging given the biphasic properties of the corneal anatomy (layers of the cornea differ between being hydrophilic or lipophilic), its cytoxicity on corneal epithelial and endothelial cells, and pH (which causes irritation).
• Systemic administration of CBD did not demonstrate a significant effect on intraocular inflammation in dogs following cataract surgery (phacoemulsification) when compared to control dogs.
• While neuroprotective and anti-inflammatory effects on the retina have been seen in diabetic rats treated with CBD, no studies evaluating the effect of CBD on retinal or optic nerve diseases have been conducted in dogs (to date).
  
  

In summary, while CBD might be considered an interesting adjunct for treating a variety of inflammatory or neurodegenerative eye diseases in dogs, the current evidence to support its benefit is fairly limited – findings have been inconsistent between animal models, ocular-specific pharmacokinetic data is lacking, and future controlled clinical trials are warranted.

Reference:
[1] Growing interest but limited evidence on the usefulness of cannabidiol in treating ophthalmic disease in dogs: a review. JAVMA (2024)Vol 262:2;S25-S31.  https://doi.org/10.2460/javma.24.06.0360