Toxocara canis is a parasitic infection that may be contracted from exposure to puppies. Toxocara may travel via the bloodstream to the eye. The parasite usually dies inside the eye, but the eye nonetheless may develop a severe inflammatory reaction to the parasite.
Inflammation from toxocara tends to affect the back two-thirds of the eye: the vitreous, retina, and choroid. Toxocara is always a consideration when we see uveitis in a child that affects the back-two thirds of the eye. We can check for toxocara exposure with a blood test; usually we can trust a “negative” test but not always (1, 2), and we may repeat the test a few months later. It’s also important to keep in mind that 5-10% of the population will have a positive test, signifying previous exposure to toxocara, but a very small proportion, probably less than 1%, of those people will ever develop significant eye disease.
Toxocara inside the eye can affect vision in may ways. Patients may develop cataract or macular edema. Toxocara may cause a severe scarring response inside the eye resulting in retinal detachment. Toxocara may also affect the optic nerve.
We usually treat inflammation from toxocara with steroids, often pills or under-the-skin-layer-of-the-eye injections. Drops alone are usually insufficient. We may sometimes advise taking a special toxocara antibiotic called albendazole.
Some patients may present with tiny inactive scars in the retina. These patients do not need any treatment. We can never know absolutely for sure but these scars may have been from a toxocara (or toxoplasma) exposure.
As a patient, be sure to tell us if you have had exposure to puppy dogs in the past five years!