Salmon Sperm and Bee Venom in Your Eye?

Excuse us, you have something in your eye: bacteria.

Pop quiz. Which part of your body is just about the same size now as it was on the day you were born?

In fact, you’re almost certainly making use of it right now.

Yup, an eyeball remains around one inch in diameter from the minute we’re born until the day we die, and it’s why the small head of an infant can make us believe that babies have big eyes. It’s actually a matter of scale.

Unless you’re reading this via some kind of whizzy text-to-speech gizmo, you’re now using your eyes, and reading our words through a thin biofilm that contains bacteria. That could explain the fuzziness.

Welcome to your ocular microbiome.

Until pretty recently, it was widely believed that, unless they were infected, our eyes were bacteria-free. But studies now show that a healthy eye does indeed contain its own ecosystem of microorganisms that remain in place despite tears and the approximately twelve times a minute that we blink.

It was in 2009 that scientist Valery Shestopalov, from the Bascom Palmer Eye Institute at the University of Miami, founded the Ocular Microbiome Project, an initiative that now has twelve collaborators in five universities.

Dr. Shestopalov’s early work showed that the surfaces of what he termed the “exposed mucosal epithelium” in the eye are densely populated with microorganisms.

In the eye, the mucosal epithelium is the wet membrane that forms the surface of the eye, and the insides of the eyelids.

Around a dozen bacterial genera dominate the eye’s conjunctiva, which is the white of the eye (the “sclera”) and the eyelids.

Interestingly, on the corneal surface (the transparent part of your eye, which covers your iris and pupil) there’s likely to be a slightly different microbial community, although again with about twelve predominant genera.

You see? Even when you’re healthy, there’s a barn load of bacteria in your eye.

But what happens when you get an infection, though?

Well, the two most common eye infections are styes and conjunctivitis (sometimes called “pink eye”).

Styes are those pesky little bumps that can form on the eyelid, generally the result of skin bacteria getting into the hair follicle of an eyelash.

Conjunctivitis can indeed be caused by bacteria, but it’s also possible that a virus or allergy could be the culprit.

Other causes can be substances that cause irritation, contact lens products, eye-drops, or eye ointments.

More on contact lenses in a moment, but first some intriguing findings about infections of the cornea, which are known as keratitis (the eye is a complicated space when it comes to naming infections).

Research has shown that during keratitis, bacterial diversity on the cornea actually reduces rather than increases, and these changes typically occur before eye infections are diagnosed, making it possible that monitoring of the ocular microbiome might form some kind of future diagnostic tool.

But what of contact lenses, then?

The US Food and Drug Administration (FDA) reports that around 30 million Americans wear them, so does this affect the bacteria in their eyes?

Yes indeedy.

A study at New York University School of Medicine (NYU) compared the ocular microbiomes of lens-wearers with those of non-wearers, and found considerable differences.

In fact, contact lens wearers tend to have an ocular microbiome which is more like their skin microbiome.

It’s tempting to jump to the conclusion that this is simply because contact lens wearers are frequently poking their fingers into their eyes (an idea many non-wearers probably flinch at), but although the NYU researchers acknowledge that this could indeed be the reason, they say it’s actually too early to be sure.

It is, however, a good time to remind all lens-wearers of the importance of thorough hand-washing before dealing with contacts.

Dr. Shestopalov’s team sequenced bacteria from contact lenses used for one day, finding relatively little diversity on their surfaces, as well as further evidence that contact lens wearers have an ocular microbiome that differs from those who don’t wear contacts.

Wearing lenses can, in and of itself, be a cause of eye problems, and estimates suggest that anywhere between 7% and 25% of contact lens wearers experience irritation and redness.

Actually, some researchers hypothesize that contact lenses make it easier for pathogens to colonize the eye by giving bacteria something to adhere to.

However, if this gives you a lightbulb moment, and makes you think about inventing an antimicrobial contact lens – well, sorry to tell you this – someone else got there first.

A medical microbiologist at the University of New South Wales in Australia is heading a team of scientists who are developing antimicrobial contact lenses by coating them with a synthetic peptide called melimine.

That’s melimine with an “i,” rather than Melamine with an “a.”

One’s an antimicrobial agent, while the other is, well, the stuff that unbreakable tableware is made from, and you wouldn’t want picnic plates in your eyes.

Although, when you read the following, you may well think the same about melimine (with an i.)

You see, melimine is a combination of two other substances – protomine, and milletin – hence its portmanteau name.

And somewhat unbelievably, protomine was originally isolated from salmon sperm, while mellitin is the principal active component of bee venom.

Quite honestly, two stranger substances to place in your eye are difficult to imagine.

Despite the thoroughly odd provenance of this antimicrobial agent, early tests on humans by the Australian scientists suggest that the melimine-coated contacts are as safe as regular lenses, and seem to be effective as an antimicrobial against two major pathogens – Pseudonymous aeruginosa and Staphylococcus aureus.

What do you get if you cross salmon sperm and bee venom?

There’s probably one heck of a good one-liner answer to that (and we’d love to hear your suggestions) but the real truth is that it’s antimicrobial contact lenses.


More Reading

Antimicrobial efficiency of covalently attached melimine onto contact lenses and in vivo safety in rabbit eyes

Biocompatibility of antimicrobial melimine lenses: rabbit and human studies.

Conjunctivitis

Eye Anatomy: Parts Of The Eye

Eye microbiome of contact lens wearers resembles that of skin

How Contact Lenses Change the Eye’s Microbiome

Ocular Microbiome Project

Pinkeye

Valery I. Shestopalov, Ph.D.

Visualizing the Ocular Microbiome

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