Contact lenses improve your vision temporarily, but they may also make lasting changes to your eyes. Twenty volunteers, including nine daily contact wearers, allowed researchers to swab various parts of their eyes, plus the skin directly below. Scientists then performed genetic tests on the swabs and on the wearers' used contact lenses. The tests showed three times more Methylobacterium, Lactobacillus, Acinetobacter, and Pseudomonas bacteria—which may cause corneal ulcers—on the eye surface of contact lens wearers than on the eyes of the other study participants, Medical News Today reports. The tests also revealed 5,245 bacterial strains found in the eyes of contact wearers were more similar to those in eyelid skin than the 5,592 bacteria strains in the eyes of non-wearers, according to a news release. Researchers suggest the pressure of the lenses might change the bacteria in the eye, or the changes may appear due to repeated contact with fingers.
A doctor tells LiveScience that millions of people use contact lenses without issue, but complications that do arise are often serious. As the bacteria found in greater quantity in the eyes of lens wearers is believed to come from skin, "greater attention should be directed to eyelid and hand hygiene to decrease the incidence of this serious occurrence," the study author says. "Our research clearly shows that putting a foreign object, such as a contact lens, on the eye is not a neutral act," a researcher adds. "These findings should help scientists better understand the longstanding problem of why contact-lens wearers are more prone to eye infections than non-lens wearers." Interestingly, the study found Staphylococcus bacteria, often tied to eye infections, was actually more abundant in non-lens wearers—a discovery that has stumped researchers so far. (Researchers warn improper lens care could make you blind.)