A man and a woman, both in the United Kingdom, became blind in one eye due to an infection - called acanthamoeba keratitis.
To see the extent of the infection, doctors used a special green dye.
The picture was published with an account of the infection in the New England Journal of Medicine.
The parasite is common in water, air, and soil, but doesn't normally cause problems unless it gets trapped under contact lenses.
The woman had a partial cornea transplant, but still lost vision.