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Eyeworm Infection in Dogs

Various health issues can cause a dog’s eyes to become red, swollen, and watery. Among the common culprits are wounds, infections, allergies, anatomical irregularities, and foreign objects stuck on the eye’s surface. However, it may surprise you to learn that a parasite known as an eyeworm could also be responsible. Keep reading to discover more about eyeworms in dogs and how they can be treated and prevented.

Symptoms and Types

Predictably, the presence of a worm residing on a dog’s eye can be highly irritating, particularly because Thelazia possess sharp serrations on their outer surface, capable of causing damage to the delicate structures of a dog’s eye. In response to this, the body generates significant inflammation, leading to redness in the eye and surrounding tissues, conjunctival swelling (mucous membranes around the eye), excessive tearing, itching, and squinting. In some cases, the cornea (the clear outer surface of the eye) may develop ulcers or scars. When a dog has only a few eyeworms, their eyes might appear nearly normal, whereas heavily infected dogs typically exhibit more severe symptoms. The worms themselves are often visible upon close examination of a dog with eyeworms. These worms are white to cream in color, slender, and can measure between 10 to 15 millimeters (approximately one-half of an inch) in length. Thelazia may be observed on the eye’s surface but can also be found beneath the eyelids (including the third eyelid) and within the ducts responsible for carrying tears to and from the eyes.


Eyeworms, with Thelazia californiensis being the most prevalent species, are transmitted to dogs through contact with specific types of flies. Research suggests that canyon flies (Fannia benjamini complex) serve as the primary carriers of eyeworms in the western United States, although other flies may play a role in different regions. Thelazia californiensis and other eyeworm varieties have been detected across various parts of the globe. The lifecycle of eyeworms is relatively simple: Adults residing in the eyes of an infected animal reproduce and lay eggs. When a fly feeds on the tears of the infected animal, it carries away larvae hatched from the eggs. These larvae mature within the fly and migrate to its mouthparts, eventually being transferred to the eyes of another animal when the fly feeds again. Eyeworms have the potential to infect dogs, cats, wildlife, livestock, and even humans.


Veterinarians typically diagnose eyeworms in dogs primarily through a physical examination. In some cases, it may be necessary to administer a topical anesthetic to numb the dog’s eyes or sedate the dog to facilitate a thorough examination under the eyelids.


To address eyeworms in dogs, the primary method involves physical extraction of the worms. Typically, a veterinarian administers a topical anesthetic to the eye’s surface or sedates the dog for the procedure. Using forceps or a sterile saline rinse, the worms are carefully removed. Additionally, veterinarians may recommend medications to eradicate the parasites, such as ivermectin, moxidectin, imidacloprid, or selamectin, depending on the circumstances.

For dogs experiencing severe eye inflammation due to eyeworms, topical or systemic anti-inflammatory drugs may be necessary to alleviate swelling, redness, and irritation. Antibiotics for dogs might also be prescribed to treat or prevent secondary bacterial infections. The selection of treatment modalities is at the discretion of the veterinarian, tailored to the individual case.

Living and Management

It’s important to closely observe dogs recovering from an eyeworm infection. If symptoms worsen at any time or show no signs of improvement within a week, it’s advisable to reach out to your veterinarian for guidance and further evaluation.


To prevent eyeworms in dogs, it’s recommended to keep pets indoors when flies are active, as this would significantly reduce the risk of infection. Studies have indicated that flies capable of transmitting eyeworms are present throughout the year in Southern California, though fly activity levels may vary in other regions.

If avoiding flies is not feasible, consider using a dog-friendly fly repellent or a medication designed to eliminate parasites, such as oral milbemycin, as part of a preventive regimen. Consult your veterinarian to determine the safest and most effective preventive measures for your dog.

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