Pathology of ocular onchocerciasis: human and experimental.

Involvement of the outer eye in Onchocerca volvulus infection is characterized by an inflammatory process around degenerating microfilariae. Individual microfilariae in the cornea may be associated with localized punctate lesions or, especially when present in large numbers, may provoke a sclerosing keratitis due to invasion by fibrovascular pannus from the limbal conjunctiva. Anterior uveitis develops in some patients and can be either granulomatous, probably as a result of direct microfilarial invasion of the iris and ciliary body, or non-granulomatous, in which case the inflammation is likely to be a response to free microfilarial antigens. Posterior segment involvement takes the form of either inflammatory or atrophic lesions, or both. It is possible that the marked atrophy of the retina and choriocapillaris seen in some cases is largely attributable to preceding choroiditis and that the optic nerve atrophy has a similar pathogenesis.