Eyeworms are a type of parasite that are either Thelazia californiensis or T. callipaeda parasites. They are found in cats, dogs, and other animals as well as humans. Usually this parasite is found in the western United States and Asia. Measuring about 0.5 to 0.75 inches, or seven to 19 millimeters, and a white color they move rapidly in snake-like motions across the eye. In a single conjunctival sac up to 100 eyeworms can exist, and they can also be found in the sac, tear ducts, or even on the conjunctiva under the third eyelid, or nictitating membrane, and eyelids. The common house fly and other filth flies act as migrating hosts between the parasite and the target. They deposit infective eyeworm lawvae on the eye while feeding on secretions from the eyes of dogs and other animals.
The most apparent symptoms of eyeworm disease include opaque corneas, slow-healing sores on the corneas, inflammation, excessively watery eyes, inflammation of the conjunctiva, and, in very rare cases, blindness. Forceps are used to observe and remove the parasites after applying local anesthetic to the eye and surrounding area. In some cases medication given by injection has been shown to effectively rid the eye of Thelazia. Specific ointments or eye solutions might also be successful at eliminating the parasite. It is important for caretakers of dogs who have this condition to consult a veterinarian as soon as possible, as each case is different and only a trained veterinarian can design and administer the proper treatment plan.