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Posted on 08-03-2015

After comparing the quantity and types of bacteria on the surface of the eyes in contact-lens wearers and non-wearers, those wearing contacts had higher microbial diversity. The contact wearers’ eye microbiome resembled more closely the microbiome of the skin than that of the eye, with three times more of the following:

Methylobacterium, found in soil, sewage, and leaves
Lactobacillus, found in the digestive and urinary tract
Acinetobacter, found in soil and water (and thought to be responsible for the majority of infections)
Pseudomonas, found widely in the environment and may lead to ear infections and other serious issues, including corneal infection
This is an important news for the 71 million contact lens wearers worldwide,3 as some of the increased microbes are linked to inflammatory eye conditions, such as conjunctivitis, keratitis (corneal infection), and endophthalmitis. This may be one mechanism by which using contact lenses increases the risk of eye diseases and infections.

The altered microbiome is thought to be the result of fingers habitually touching the eye, transferring in microbes that wouldn’t ordinarily exist in such high numbers. It could also be due to alterations to the eyes’ immune system due to the lens’ direct pressure on the eye.4 Another alternative is the contact lenses may favor skin-like bacteria in the eye.

Senior study investigator Maria Gloria Dominguez-Bello, a microbiologist at NYU Langone Medical Center, stated:

“Our research clearly shows that putting a foreign object, such as a contact lens, on the eye is not a neutral act.”

Is Your Eye Microbiome Linked to Dry Eye?

Although the eyes’ microbiome is only beginning to be understood, there’s reason to believe it may play a significant role in eye health. According to a proposed study being sponsored by the Singapore National Eye Center:

“Over the course of evolution, various microbes, especially bacteriae, have come to colonize the ocular [eye] surface as commensals. The commensals have a role to maintain the homeostasis of the ocular surface.

The innate immunity of the ocular surface is very active, and consists of active mechanisms to suppress inflammation. For example, there exist macrophages, dendritic cells, suppressor cells, regulatory cells, B cells, IgA, lysozyme, anti-microbial peptides and barriers against external agents.

The normal commensals of the ocular surface maintain a basal level of activation of innate defense by stimulating the pattern recognition receptors on ocular surface epithelial cells.

This normal composition of microbes is important since inflammation and infection will result if there is introduction of a pathogenic strain that overcomes the flora, or if a dominant strain secretes excessively immunogenic products.”

The proposed study wants to determine if dry eye may, in fact, be microbial in origin. “Since dry eye is a known inflammatory disease of the ocular surface, this is one way that microbes can contribute to the pathology,” they note.

The Ocular Microbiome Project

The Human Microbiome Project, which was initiated in 2008 and funded by the National Institutes of Health (NIH), aimed to “characterize microbial communities found at multiple human body sites and to look for correlations between changes in the microbiome and human health.”

Unfortunately, this multimillion-dollar effort did not include the surface of the eye. So, in 2009 researchers at Bascom Palmer Eye Institute in the US initiated the Ocular Microbiome Project.

While it was once believed the surface of the eye was relatively devoid of microbial life, due to tears and blinking “washing” it away, research from the Bascom Palmer Eye Institute found the opposite, that the surface is “populated densely” not only with bacteria (about a dozen different types were dominant) but also viruses.

“People can have a huge variation in microflora and still have healthy eyes, making our job difficult, but really amazing,” researcher Valery Shestopalov told The Scientist.

Also interesting, the researchers found that only about half as many bacterial varieties were presented during keratitis infections, which are serious infections of the cornea.

The most prominent strains were Pseudomonas, and the changes to the microbiome occurred long before the eye infections were diagnosed, which suggests such changes could be used to diagnose the infection earlier, or perhaps could one day be changed to prevent the infection entirely.

In this case, the researchers believe contact lens wearers may be more prone to infections, because the lenses provide a surface upon which pathogens can colonize. Separate researchers have developed an antimicrobial contact lens they believe will counteract the problem, without altering the normal, commensal bacteria of the eye.

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