Ocular surface inflammation is the most common reason for dry eye syndrome. Inflammation can come from a lot of sources, of which, the main culprit is what's happening on or inside the eyelids.
The most common eyelid issue is blepharitis, which can be broken down into the anterior and posterior varieties. Anterior blepharitis is inflammation of the skin near the eyelashes and inside the eyelash follicles. It can be caused by bacterial overload, seborrhea, rosacea, and/or demodex. Posterior blepharitis is when the conjunctival layer that lines the inside portions of the eyelids and the eyeball become inflamed. This typically occurs because whatever source is creating the anterior blepharitis, is also leaking into the eye and causing the same inflammatory issue. To top this off, the meibomian glands sit right underneath the conjunctiva, and are also predisposed to inflammation as well. This causes meibomian gland dysfunction, and a poor quality of oil on the tear film. So there really is a cascade of events that occur, and typically if you have anterior blepharitis, you also have posterior blepharitis and meibomian gland dysfunction.
The front surface of the eyelids and eyelash follicles are susceptible to infestation of bacteria and yes, mites. Mites?!?!?!? Ew.
Colonies of bacteria live around this area, and sometimes an over proliferation of some strains, namely the staphylococcal variety, occur. The biological byproducts of the bacteria cause an immune reaction on the skin that causes inflammation. The same is true with Demodex (mites), as they colonize the inner portions of the eyelash follicles and secrete toxins that end up causing inflammation. Studies suggest that past the age of 17, we all have mites that live on us. But some people are more prone to infestation because, similar to bacterial colonization, the environment of their skin provides a more friendly environment.
Chronic skin issues like seborrhea and rosacea will cause inflammation by themselves. Plus, just like Demodex, they create an environment that supports some bacterial strains more than others.
In my experience, Rosacea is more prone to causing dry eye than seborrhea, because it infiltrates the eyelids and conjunctiva. It causes new vascular growth below the skins surface and that includes the eyelids and conjunctiva. Those new vessels are leaky, and are more likely to dump pro-inflammatory mediators onto the ocular surface, causing chronic inflammation. If facial rosacea is present, more than likely, there will be an ocular component as well. Dry eye caused by rosacea can be difficult, because curing it is very difficult, if not impossible. However, there are some pulse light treatments available that treat the skin on the face, that are having positive benefits to dry eye from rosacea. More on that in Part 4 of this series.
Meibomian Gland Dysfunction
Because inflammatory conditions on the eyelids and lashes are typically chronic issues, inflammatory products have a greater opportunity to leak into the eye, causing chronic inflammation and dysfunction. This happens inside the meibomian glands as well. The inflammatory process changes the quality of the oil that is made and this changes the quality of the tear film, often creating a higher rate of aqueous evaporation. As the issue drags on, corneal or conjunctival injury occurs, causing them to send out more inflammatory mediators. Not to mention that the cornea is highly innervated with sensory nerves. When there is injury there, pain, burning, and excessive tearing begin.
When meibomian gland dysfunction is present, bacteria can infiltrate the glands causing hordeola, or styes. So the development of a stye or the recurrence of styes means that there is underlying gland dysfunction. And with gland dysfunction, the development of dry eye syndrome is most likely on its way. There may not be symptoms for years, but over time chronic inflammation will pave the way.
So you can see the domino effect that occurs when something goes wrong on the eyelids. Insidious issues that, as people, we really don't know are happening until we become symptomatic.
The next part of this series will be dedicated to some of the treatments available to dry eye caused by some of the issues I have discussed in this post.
Hope all is well!
Mike Morabito, O.D.
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