John Matthews of Bellevue, Iowa didn't know why he continuously suffered last year from hazy vision and kept seeing dark spots.
His ophthalmologist, Dr. James Folk of the University of Iowa Hospitals and Clinics, gave Matthew the shocking diagnosis back in December: Matthew had a parasitic worm in his eye that was eating away at his retina.
While hearing about a worm eating a person's eye may be stomach-churning, experts say parasitic infections occur frequently around the world -- and even in the United States. Such cases often serve as an unsettling reminder that despite modern medicine, humans are not always at the top of the food chain.
Though the eyes are not usually the most commonly infected organs, eye worms are certainly not unheard of.
"The three most common parasitic infections affecting the eyes are toxocariasis, loaiasis [infection with the Loa loa worm] and African river blindness," said Dr. Peter Hotez, chair of the Department of Microbiology, Immunology and Tropical Diseases at George Washington University in Washington, D.C.
On the next few pages, ABC News takes a look at this case of parasitic infection, as well as other cases of parasites that have taken up residence in other parts of the body -- along with some expert advice on how to rid yourself of the worms.
Matthews told ABC's Cedar Rapids, Iowa affiliate KCRG that while the diagnosis didn't freak him out, he definitely wanted the worm out of his eye.
"I was like, 'Get it out. What do we do now?'"
After looking at photos of Matthews' eye, Folk saw the worm.
"It was only about a twentieth of an inch long, and it went under the retina," said Folk. "I was pretty sure it was Baylisascaris procyonis."
Baylisacaris procyonis is a parasite that seems to have a fondness for the eyes.
"It hatches in the gut and somehow makes its way to the eye and the brain," said Folk.
It's very rare, and because an infection with the worm could cause blindness, Folk said he was very happy to see it so he could kill it. He took aim at it with a medical laser.
"It was writhing and wriggling and trying to get out of the way," said Folk. "When we started to heat up the laser, it got very mad."
Folk's laser won the battle and killed the worm. Unfortunately, the worm did permanent damage to the retina and the optic nerve, though Folk said Matthews' vision seems to be improving.
Folk said he doesn't know how Matthews may have come in contact with Baylisacaris procyonis, but said raccoons often carry millions of worm eggs with them. Matthews may have accidentally ingested something while while on one of his frequent hunting expeditions or trips to foreign countries.
"I'm surprised it's not more frequent. Those eggs can last a long time," said Folk.
Matthews' story is just one of many that make the rounds of medical journals and media reports.
Take the case of 21-year-old Kenneth Watson, who was also infected by a retina-eating parasite.
When Watson was 16 and living in Hardy, Ark., a gnat flew into his eye. He thought nothing of it, because gnats and other insects are a part of life in the southern U.S.
But two weeks later, he knew something was wrong when suddenly, he couldn't see anything except for a large, dark dot.