Case description: A 4-year-old Hanoverian gelding was evaluated because of a mobile worm-like structure in the right eye.
Clinical findings: Ophthalmologic examination of the right eye revealed a white, thin, coiled, mobile parasite, which was presumed to be a nematode, located in the ventral portion of the anterior chamber of the eye; there also were vitreal strands located temporally and inferiorly near the margin of the pupil. Results of ophthalmologic examination of the left eye were unremarkable.
Treatment and outcome: The horse was treated with a neomycin-polymyxin B-dexamethasone ophthalmic solution applied topically (1 drop, q 8 h) to the right eye and penicillin V potassium (22,000 U/kg [10,000 U/lb], IV, q 6 h). The horse was anesthetized. A stab incision was made in the cornea, and a viscoelastic agent was infused around the parasite. The parasite was extracted via the incision by use of an iris hook and tying forceps. The horse had an uncomplicated recovery from the procedure and retained vision in the right eye. Gross and microscopic examination was used to identify the parasite as an adult metastrongyloid nematode consistent with a fully developed male Parelaphostrongylus tenuis.
Clinical relevance: To the authors' knowledge, this is the first report of intraocular parelaphostrongylosis in a horse. This report provided evidence that vision could be retained after treatment for intraocular P tenuis infection in a horse.