A small but intriguing new study may shed light on why people who wear contact lenses are more likely to get certain eye infections.
Using sophisticated genetic testing, researchers from NYU Langone Medical Center analyzed thousands of types of microorganisms and bacteria found in people's eyes, and discovered that contact lens wearers tend to harbor different bacteria than people who don't wear contacts -- including several types of bacteria that don't normally live in the eye.
"It's a very interesting study and there were some very interesting results," Dr. Christopher Starr, associate professor of ophthalmology at Weill Cornell Medical Center in New York, told CBS News, though he noted that the findings should be considered preliminary, since the study involved only 20 people and has not been published in a peer-reviewed journal.
"They found upwards of -- over 5,000 unique types of bacteria that reside on the eyeballs of contact lens wearers and non-contact lens wearers," Starr said. "A lot of those bacteria are ubiquitous, they're everywhere, they're on different parts of the body. And I suspect that if you tested other parts of the body you'd find a large variety of bacteria as well."
But the number alone was only part of the story. "One of the interesting discrepancies between contact lens wearers and non-contact lens wearers was that the bacteria in the surface of the eye in those who wear contacts was very similar to what we find in the eyelids and the skin," Starr said.
The study singled out four types of bacteria that were three times more common in contact lens wearers. Two of them -- Methylobacterium, typically found in soil, sewage and leaves; and Lactobacillus, a "friendly" bacteria that lives in the digestive and urinary tract -- "that sounds gross," Starr said, but they're not normally harmful.
The other two -- Acinetobacter and Pseudomonas -- are greater cause for concern. Starr said Acinetobacter only occasionally causes infections, but "Pseudomonas, that worries me. That scares me....Pseudomonas is a well known, very aggressive cause of really bad eye infections." It can cause corneal ulcers, he added, commonly associated with people who wear contact lenses. In extreme cases, patients can lose their eyesight.
The NYU researchers said their findings could help explain why contact lens wearers are more prone to eye infections, and suggested that a better understanding of the microbiome might someday help prevent infections.
In the meantime, Starr offered some practical advice to minimize the risk.
"It's very easy to look at this story and say I'm never going to wear contact lenses," he said, but with proper precautions they can be used safely.
"Probably the safest bet with contact lenses is the daily lenses -- you put in a fresh pair in the morning; at the end of the day, toss it in the garbage," Starr said.
For longer-lasting lenses that are worn day after day for two weeks or a month at a time, he advised, "It's very important that those lenses be cleaned appropriately." Never rinse lenses with tap water or bottled water, which are full of bacteria.
Do contact lens wearers ever need to give their eyes a break? Not necessarily, Starr said. "If you're tolerating the lenses well, and you don't have any symptoms, and you can go a whole day with no fatigue or irritation or dryness at the end of the day, it's OK to wear your contact lenses. If they fit well, if you're tolerating the solutions and the materials, there's no reason to not wear your lenses all day, every day."