Eyeworms (Thelazia californiensis and T. callipaeda) are parasites found in dogs, cats, and other animals, including humans, in the western United States and Asia. They are whitish, 0.5 to 0.75 inches (7 to 19 millimeters) long, and move in a rapid snake-like motion across the eye. Up to 100 eyeworms may be seen in the conjunctival sac, tear ducts, and on the conjunctiva under the nictitating membrane (third eyelid) and eyelids. Filth flies (including the common house fly) serve as intermediate hosts and deposit the infective eyeworm larvae on the eye while feeding on secretions from the eyes.

Signs include excessive watering of the eyes, inflammation of the conjunctiva, opaque corneas with slow-healing sores, and rarely, blindness. After a local anesthetic is applied, diagnosis and treatment are accomplished by observing and carefully removing the parasites with forceps. Some veterinarians have reported the successful elimination of Thelazia infections from dogs with injected medication. Certain eye solutions or ointments also may be effective. Your veterinarian will evaluate your pet's situation and take the most appropriate treatment approach.

To diagnose, examine, and remove eyeworms, a veterinarian might numb the affected areas.

Last full review/revision July 2011 by Kirk N. Gelatt, VMD; David G. Baker, DVM, MS, PhD, DACLAM