Retinal pigment epitheliopathy and neuroretinal degeneration in ascarid-infected eyes.

The generalized choroidal and retinal response to a focal nonreplicating infection of the eye with ascarid larvae was examined in an animal model. Intravitreal injection of Ascaris suum larvae in guinea pigs induced a diffuse eosinophilic choroiditis, retinal pigment epitheliopathy and neuroretinal degeneration, distant from focal reactions about larvae. As the choroiditis progressed, inflammatory cells separated the choriocapillaris from Bruch's membrane, and the endothelial cells lost their fenestrations. Focal disruption of the elastic and outer collagenous layers of Bruch's membrane occurred, but inflammatory cells rarely invaded the retina. Progressive generalized degenerative and proliferative RPE changes produced a multilayered RPE with loss of cell polarity, RPE basal infoldings and apical microvilli, formation of multiple giant cystic spaces, and proliferation of subretinal fibroblasts. Early loss of photoreceptor outer segments progressed to a generalized disruption of the outer neural retina and cystoid retinal degeneration. Eosinophil mediators and alterations of the choriocapillaris may contribute to the generalized progressive retinal degeneration distant from a parasite larva in ascarid-infected eyes.