Invasion of the mouse eye by Onchocerca microfilariae

Onchocerca cervicalis microfilariae (mf) were injected s.c. into the scalp between the eyes of CBA/H mice. Invasion was followed by slit-lamp biomicroscopy and H & E stained serial sections at varying times post infection. The first mf observed were found 24 hr p.i. on the corneal surface in tear fluid. At 48 hr mf were observed actively swimming in the anterior chamber and by 3 d in the corneal stroma. Histologically mf appeared in orbital muscle connective tissue, subcutaneously in the eyebrows at the eyelid/conjunctiva junction from 6 hr p.i. By 12 hr some mf had moved into the suprascleral muscle junctions, the sclera and into the superior corneal stroma. By 24 hr mf were present in larger numbers in all these sites. Mf were found in all eyes up to 42 d p.i. No mf were seen in any sections of the retina or optic nerve. Rabbit antiserum raised to mf, used in an avidin-biotin immunostain to check whether mf might have been hidden within the retinal nuclear layers, revealed no mf although they were plainly seen in other ocular tissues. Retinal invasion was induced by injection of mf into the lateral tail vein: serial sections revealed mf associated with blood vessels in the sclera, suprascleral muscle blocks and inner plexiform layer of the retina from 5 min p.i.