New research has discovered that people who wear contact lenses have different microorganisms living on the surface of their eyeballs than those who do not.

Researchers believe that these differences may explain why people who wear contacts tend to have more eye infections than those who do not.

"As other body sites such as gut, skin and mouth, the eye has a normal community of bacteria, expected to confer resistance to invaders," said senior author Maria G. Dominguez-Bello of New York University School of Medicine.

"Despite being important in ophthalmology, the eye microbiome has been largely neglected, and its functions remain unknown."

For the new study, researchers swabbed various parts of the eyes, including both the surface of the eyeball and the skin directly beneath the eye of nine contact lens wearers and 11 people who don't wear contacts at three different times. They then used metagenomic sequencing to identify the specific microorganisms in each swab.

For people who wore contacts, the micoorganism population living on the eye was more similar to what was found on the eyelid skin compared to non-lens wearers. Researchers believe that the contacts may transfer bacteria from the skin of the finger to the surface of the eye.

Researchers also found that there were more than 5,000 bacterial strains on the eye's surface and there are 2,000 strains on the skin directly beneath the eye. This was unexpected since human tears contain antibacterial compounds, Dominguez-Bello said.

People who didn't wear contacts tended to have more bacterial strains compared to those who do wear contacts, but for lens wearers the proportion of bacteria from the Methylobacterium, Lactobacillus, Acinetobacter and Pseudomonas families was three times as great as for non-lens wearers.

"The findings indicate there are significant differences in diversity of bacterial sequences between contact and non-contact lens wearing subjects and that taxonomic units in the contact lens wearing group were more like the skin than the normal eye," said Dr. Stephen Pflugfelder, who studies cornea and ocular surface diseases at Baylor College of Medicine in Houston, Texas.

"Because they did not perform cultures, the study didn't determine if these sequences were from live viable bacteria or dead bacteria that may have been transmitted by the finger skin," Pflugfelder, who was not part of the new research, said.

Further studies will have to be performed to determine if these bacteria are transferred to the lens from the fingers or if the lenses simply act to favor skin-like bacteria in the eye. "It's too early to give advice yet, but the results start to indicate why contact lens wearers are more prone to have eye infections than non wearers," Dominguez-Bello said.

The findings were reported at the annual meeting of the American Society for Microbiology held on May 31 in New Orleans.