CEDAR RAPIDS, IA (CNN) - When two dark spots appeared in his vision and his eyesight became a little blurry, John Matthews paid a visit to the doctor.
The Cedar Rapids, IA man loves to hunt turkeys and travel to foreign places like Mexico. But during one of those adventures, something crawled inside his body.
"It's so small, you couldn't even see it, feel it," Matthews said.
He described the sensation as "kind of like looking through a muddy lens."
Doctors struggled to diagnose what was wrong with Matthew's left eye. Dr. James Folk of University of Iowa Hospitals and Clinics found the problem: a worm invisible to the naked eye was damaging Matthew's eyesight.
"Just by luck," Folk said, "the first picture we looked at, we saw the worm right in the middle of the retina."
It turned out that a microscopic worm was swimming around inside Matthews' eye.
"The worm goes into the gut, digests in the gut, and actually doesn't crawl through the blood vessels but crawls through the tissue all the way to the eyes and the brain," Folk said.
Once the worm completed its journey, Folk said it was living underneath Matthews' retina and feeding on it.
As soon as he discovered the problem, Folk armed himself with a laser and put the worm in the cross-hairs.
Matthews was awake the whole time. He said that he was never scared. He just kept thinking, "Hurry up and kill the thing. Good luck shooting, doc."
Folk said that when he hit the worm with the laser, it got upset.
"The thing was just thrashing around violently. It would be like one of those titan movies of Iron Man or something," Folk laughed.
Although the worm is dead, Matthews must continue to do computer exercises to strengthen his eye. His vision has improved, but it may never return to normal.
"His sharp-shooting days are over," Folk noted.
For the rest of his life, John will be on a different kind of hunting expedition to see if any doctor can restore his eyesight.
As for the worm, it is decomposing inside John's eye because it was too dangerous to remove.
There are only about 15 known cases in the world like Matthews'.