Thelazia gulosa: a type of worm that very rarely has been reported to infest human eyes. T. gulosa is known as the cattle eyeworm. Dogs, cattle, and horses are the usual hosts for this worm; the larvae (immature forms) are shed from the affected animal's eyes and are ingested by flies. The infested fly then transfers the larvae to the eyes of the next host. Rare cases of transmission to humans have been described, in which the larvae mature, causing adult worms to be found in the lining tissues of the human eyes. Symptoms can include irritation, excess tear production, inflammation, photophobia, and even blindness in severe cases. The condition is known as thelaziasis.