River blindness is caused by -

pathogenesis and clinical features The infective larvae deposited in the skin by the bite of the vector develop at the site to adult worms .Adult worms are seen singly, in pairs , or in tangled masses in the subcutaneous tissues ocular manifestations range from photophobia to gradual blurring of vision , progressing to total blindness. Ref : panikers textbook of medical parasitology 8th edition page 222