Thursday, January 13, 2011

Itchy eyelids? Crusty eyelids? The reality of Demodex

What's Demodex? They are mites, which are microscopic little critters with eight legs. They belong in the same class  of animals as spiders. While most have heard of house dust mites, few have heard or come across demodex, except maybe dog owners. This is despite Demodex infesting many of us, only we are unaware of their presence most of the time.

Demodex are readily accessible to inspection by most ophthalmologists, only many ophthalmologists are also unaware of their presence. When they infest the lash follicles, they are readily visible on high power with the slit lamp microscope. The video shows how I look for them-by pulling lightly and twirling the eyelashes. Before I do this I clean away all debris and dandruff like material with an alcohol swab. Then, pulling lightly on the lashes causes their tails to poke out, and further twirling the lash will cause the mass of demodeces to come out and lie on the skin surface. They look like tiny shiny rod shaped objects. They can then be scooped up with the tip of a forceps and I touch them lightly on the sticky side of a cellophane tape. I then stick them on a microscope slide and have a look on a compound microscope. The picture shows one that I caught recently. However, now that I've seen quite a few of them, I can readily identify them on the slit lamp alone.

So what? It seems to me that most people with blepharitis, especially anterior blepharitis and lots of debris near the eyelashes also have lots of demodex. Coincidence? Some people say demodeces are commensals. Well, I would say it's too much of a coincidence. Several papers by Scheffer Tseng have now come out about the pathological role of demodex in ocular surface disease. I still wonder about posterior blepharitis and meibomian gland disease. I often see this without demodex infestation of the lashes. It could be that there is deeper infestation within the Meibomian gland itself, by D Brevis, but we won't know for sure unless we can somehow put a scope up the gland or maybe test the Meibum by PCR for the demodex.

If you see Demodex, what do you do? Some would do nothing. I think that is reasonable if you see one or two of them in the odd follicle, and the patient is not symptomatic. But if there are lots, and the patient is itching like crazy or the lids are inflamed, then steps should be taken. Tea tree oil has been touted as being a great mite killer-but that would only work for the ones on the lashes. If there are any in the Meibomian glands one might have to resort to something  systemic like ivermectin. I don't see how the tea tree oil would get into the Meibomian glands. So there you have it-in a nutshell. My thoughts on Demodex and blepharitis. I do welcome your comments.

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