TL;DR: Eyeworms (Thelaziasis) are parasites transmitted by flies that require veterinary removal within 24-48 hours to prevent pain and permanent vision damage.
What are eyeworms in dogs?
Seeing a thin, white, thread-like parasite moving across the surface of your dog's eye is most commonly a condition called Thelaziasis, or more simply, 'eyeworms.' These parasites are typically transmitted by certain species of fruit flies that feed on eye secretions, depositing larvae that grow into visible adult worms on the conjunctiva or under the eyelids.
Are eyeworms in my dog's eye a medical emergency?
- The urgency level for eyeworms is Medium; while not immediately life-threatening, it is a painful and distressing condition for your pet.
- You should schedule a veterinary appointment within 24 to 48 hours.
- Prompt treatment is necessary to prevent chronic inflammation, corneal ulcers, or secondary bacterial infections that could permanently impair your dog's vision.
How can a photo of my dog's eye help with veterinary triage?
- Capture a clear photo or a short video of the moving worm to provide visual evidence for your veterinary team.
- Documentation is helpful because these parasites often hide behind the third eyelid or in tear ducts when the eye is being manipulated during an exam.
- Having visual evidence ensures a faster diagnosis and helps the vet prepare the necessary tools for safe extraction.
Clinical Context (Merck Veterinary Manual)
Thelazia californiensis and Thelazia callipaeda are eyeworms found in dogs (and other animals) in the USA, Europe, and Asia. These whitish worms (7-19 mm long) move rapidly in a serpentine motion across the eye and up to 100 may be present in the conjunctival sac, tear ducts, and conjunctiva under the nictitating membrane and eyelids. Intermediate hosts are filth flies (Musca spp, Fannia spp) and zoophilic fruit flies (Phortica variegata, Amiota spp), which deposit infective larvae on the eye. Clinical signs include excessive lacrimation, epiphora, ocular pruritus, conjunctivitis, keratitis with corneal opacity and ulceration, hyperemia, and rarely blindness. Diagnosis and treatment involve observation and removal of the parasites with forceps after local anesthetic. Effective treatments include ivermectin (0.2 mg/kg SC), milbemycin oxime (minimum 0.5 mg/kg PO, two treatments 1 week apart), or moxidectin 2.5% spot-on. Ocular solutions (1% moxidectin or 2% levamisole) or ointments (1% levamisole or 4% morantel) may also be effective.
Chapter: Ophthalmology, Parasitology
Source: The Merck Veterinary Manual, 11th Edition (Page 512)