noun Medical Definition of EYE WORM: a parasitic worm found in the eye: as a : either of two slender nematode worms of the genus Oxyspirura (O. mansoni and O. petrowi) living beneath the nictitating membrane of the eyes of birds and especially chickens b : any member of the nematode genus Thelazia living in the tear duct and beneath the eyelid of dogs, cats, sheep, humans, and other mammals and so