Outcomes of Vitrectomy Versus Suprachoroidal Steroid Injection in Cases of Presumed-trematode Induced Granulomatous Intermediate Uveitis

Microbial infections such as tuberculosis, toxocariasis, and toxoplasmosis can induce granulomatous uveitis in children. Also, it might be induced by non-infectious causes such as sarcoidosis, sympathetic ophthalmia, or Vogt-Koyanagi-Harada disease. Also, parasitic infestation of the eye can produce significant granulomatous uveitis with subsequent complications. Presumed trematode-induced uveitis most frequently observed in children who swim in nearby freshwater canals harboring trematode-infected snail. The term "presumed" is used to describe this type of uveitis as fragments and genetic material of the parasites could be isolated from only some of the surgically removed granulomas without signs of systemic parasitic disease. The hallmark of trematode-induced granulomatous inflammation is one or more pearl-like nodules almost always seen in the inferior quadrant of the anterior chamber (AC), which has been documented in Egypt and India. Sometimes, intermediate uveitis with snow banking and cilliary body granuloma, lens granuloma, iris granulomas and posterior uveitis could be the presenting feature of this disease. Less frequently, subconjunctival lesions or corneal lesions can also occur.

Ocular inflammation may be secondary to the reaction of the immune system of the host against the parasite or its toxic products.

Procerovum varium, a trematode, was identified as the causative agent responsible for AC granuloma in children in South India. Schistosomiasis, also known as bilharziasis, is an endemic disease caused by trematodes of the Schistosoma genus in Egypt. Relatively rare ocular involvement has been attributed to Bilharziasis, mainly in the form of granuloma reaction induced by the ova or adult worms in different ocular tissues. Schistosoma mansoni was also observed and isolated from the AC angle. The cercariae (infective stage) of the trematode can reach maturity and lay ova directly in the veins of the richly vascularized conjunctiva, which subsequently leads to the development of sub-conjunctival granuloma. In some cases, cercariae can penetrate limbal structures and gain access to the anterior chamber leading to the development of AC granuloma. This has been considered the most accepted theory that explains how the ova of the trematode or adult worms reach the eye.Case reports have traced the life cycle of the parasite Procerovum varium in patients with trematode granuloma. It is a trematode found in the conjunctival sac of the birds. When these birds come into contact with the water bodies, the adult worms from the conjunctival sac can release eggs into these reservoirs. These eggs can then hatch into miracidia. When miracidia infect the intermediate host, the snails, the miracidia mature to become cercariae. These cercariae to complete their life cycle have to reach the birds again. Humans are accidental hosts in this cycle. Children are affected when they come in contact with the water infested with the cercariae. The parasite directly enters the eyes penetrating the ocular tissues.

The ocular manifestations can be caused by either direct trauma from the parasite or secondary to the toxic products released by the organisms. There are multiple theories as to how the trematode reaches the ocular tissue. Alternatively, the trematode ova can also reach the ocular tissue from systemic circulation after it matures to cercariae. They lay eggs in the highly vascularized conjunctiva, deep episcleral plexus, limbus and anterior chamber.

Whatever be the mode of entry of these parasites, the final pathology is that the released ova cause inflammation which leads to a granulomatous reaction in the ocular tissue. The granuloma is found to have teguments or internal fragments of parasites in the centre of the lesion surrounded by neutrophils, eosinophils. mononuclear cells, lymphocytes, macrophages, multinucleated giant cells and fibroblasts. Splendore-Hoeppli phenomenon is described in the histopathological evaluation of a few granulomas in the study by Rathinam et al. and others. Splendore-Hoeppli phenomenon is characterized by the presence of radiating intensely eosinophilic material around the parasite. Finally, when the inflammation settles down, there is deposition of collagen in the places of granuloma.