Understanding the Microbiome of the Eye

There has been a lot of talk the past several years about the human body’s microbiome. This is the complex network of [beneficial] bacteria (and fungi and viruses even) that help to protect the body and ensure optimum function.  Most of this discussion, though, has been about the microbiome of the gut and, more recently, the skin. 

But a new discussion is entering the fray:  the microbiome of the eye.  Indeed, your eyes are also home to a unique community of microbes that, when out of balance, can lead to a handful of different types of eye-related disease.

A recent study indicates that bacteria live on the surface of the eye, acting as a stimulant for protective immunity functions. Scientist are now starting to learn more about the microbial factors that we may be able to exploit, and in so doing develop innovative therapies for a wide range of eye disorders. This might lead to emerging treatments for things like Dry Eye Disease, corneal scarring, and Sjogren’s Syndrome.

The theory, then, is that we may one day be able to engineer bacteria to directly and effectively treat human eye diseases. 

All of this comes after about a decade of research involving the human microbiome and ocular health.  As a matter of fact, the idea that a microbiome contributes to ocular health has been controversial at best.  Actually, scientists used to believe—indeed even just a few years ago—that healthy eyes do not have an organized microbiome. Newer studies now show that bacteria from the air, hands, and even the eyelid margins could also be present in the eye.  Of course, those who did believe that these bacteria existed also thought they were easily killed or washed away (by tears, etc).

It is actually only very recently that scientists have identified how the human eye harbors a “core” microbiome. Furthermore, since determining this microbiome, scientists have also found that this “core” microbiome is dependent on age, contact lens wear, ethnicity, geographic region, and state of disease.  

This “core” microbiome is limited to only four genera of bacteria:  Staphylococci, Diphteroids, Propionibacteria, and Streptococci.  The core microbiome is also, apparently home to the torque teno virus—which is often implicated in intraocular diseases—because it is present on approximately two-thirds of the surface of healthy eyes. 

Essentially, this discovery can lead to better treatment by understanding what conditions are related to bacterial and viral infection. By balancing the eye microbiome, researchers say, it could prevent up to 1 million eye doctor visits and save upwards of $174 million in the US every year.