Thelaziasis is an ocular infection of several mammals caused by nematodes of the 
genus Thelazia (Spirurida, Thelaziidae). The adults live in the lachrymal ducts 
and conjunctival sacs of infected animals, and transmission occurs by means of 
different species of muscids. T. rhodesi, T. skrjabini, and T. gulosa affect 
mainly cattle, inducing conjunctivitis, keratitis, and ocular discharge. This 
article describes the morphological features of adult T. rhodesi, T. skrjabini, 
and T. gulosa by scanning electron microscopy and highlights the most relevant 
differences for their identification.