Researchers have identified a diverse set of microbes in the eye of daily contact lens wearers.
These are not found normally in the eye and imply that wearing the lens increases exposure of eye to many new infections.
The study also identified a germ behind increasing cases of corneal ulcers in the skin, calling for more eye hygiene among lens users.
The team at NYU Langone Medical Center in New Orleans identified microorganisms in the contact lens users' eye which more closely resemble those found on the skin of non-wearers.
The eye surface, or conjunctiva, has surprisingly higher bacterial diversity than the skin directly beneath the eye. There was three times the usual proportion of Methylobacterium, Lactobacillus, Acinetobacter and Pseudomonas bacteria in the eyes of the study's nine contact lens wearers than is typically found on the surface of the eyeballs of 11 other men and women in the study who did not wear contact lenses.
In terms of germ diversity, the eye microbiome (range of organisms) of contact lens wearers had a composition more similar to that of the wearer's skin than the eye microbiome of non-lens wearers.
"Our research clearly shows that putting a foreign object, such as a contact lens, on the eye is not a neutral act," says senior study investigator and NYU Langone microbiologist Maria Gloria Dominguez-Bello.
The next step would be to see whether the changes in the eye microbiome of lens wearers are due to fingers touching the eye, or from the immune system being affected by lens's direct pressure.
"There has been an increase in the prevalence of corneal ulcers following the introduction of soft contact lenses in the 1970s," says study co-investigator Jack Dodick, MD, professor and chair of ophthalmology at NYU Langone.
"A common pathogen implicated has been Pseudomonas. This study suggests that because the offending organisms seem to emanate from the skin, greater attention should be directed to eyelid and hand hygiene to decrease the incidence of this serious occurrence," he says.
Researchers took swabs of various parts of the eye, including the eye conjunctiva, as well as along the skin directly beneath the eye. The swabs and used contact lenses were then subjected to genetic analysis to identify the bacteria.
Around 5,245 distinct bacterial strains and subtypes were identified in the eye conjunctiva of lens wearers, and 5,592 strains were identified in the eyes of non-lens wearers.
A similar but different composition of 2,133 strains and subtypes were identified in the skin directly beneath the eye of those with contact lenses, while 3,849 distinct bacteria were identified in non-lens wearers.
Surprisingly, more Staphylococcus bacteria, which are linked to eye infections and more prominent on the skin, were found in the eyes of non-lens wearers, and researchers do not yet have an explanation for the disparity.