Fundus lesions in the rabbit eye following inoculation of onchocerca volvulus microfilariae into the posterior segment. I. The clinical picture.

Live microfilariae of the Cameroon forest and Sudan-savanna strains of Onchocerca volvulus were inoculated into the vitreous or into the subretinal layers of the eyes of rabbits. The lesions produced are described, and are compared with those seen in control animals, which had received inocula of microfilariae-free saline supernate introduced with a similar degree of operative trauma. Control rabbits showed only minor pigment disturbance in the retina and choroid, near the healed operation scars. Infected animals showed evidence of an inflammatory process in the eye, lasting for up to 4 weeks. Fundus lesions developed following inoculation of microfilariae into the vitreous, but they were more frequent and more severe following subretinal inoculation. The lesions produced were: pallor, vascular narrowing, and flattening of the optic disc; subretinal inflammatory exudate, giving rise to a disturbance of pigment in the retinal pigment epithelium; scattered, small choroidoretinal scars, and larger circumscribed areas of choroidoretinitis, sometimes accompanied by optic atrophy. In many eyes inoculated with microfilariae the wincing reflex was lost, indicating some visual impairment. Many of the lesions were similar to those seen in human patients with onchocerciasis, but they developed much more rapidly. Microfilariae inoculated intravenously, or into the periocular tissues, were not observed to penetrate into the eye-ball.