Two reports in a week are driving home the reminder not to shower or swim with contact lenses.
A man and a woman, both in the United Kingdom, became blind in one eye due to an infection - called acanthamoeba keratitis.
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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.
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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.