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Minimizing Demodex mite populations on the lids contribute toward a pro-inflammatory environment of the lids. Eliminating parasitic overpopulation in the lids and lashes decreases inflammation and provides a healthier environment for the ocular surface to function at its best.
Over the past 10 years we have witnessed a striking transformation in the way we as eye physicians approach ocular surface disease. We have seen definitions tighten and become more descriptive to better indicate what we should understand about the pathophysiologic disease process of each subcategory. And while the movement toward a more detailed understanding of meibomian gland dysfunction, dry eye, and blepharitis has brought us great advances, the truth is that due to the close proximity and continual interaction of the system as a whole, there is much overlap among these disease entities, and most patients have more than one of these processes occurring simultaneously.
Enter another “new” (yet surprisingly old) twist: the presence of a small ectoparasite which has been for the most part ignored for many decades: Demodex. This small creature is something we were briefly educated about in school; however chances are high that we never actually witnessed our attendings diagnose or present to us a patient with mites or even saw a photo of what they looked like. Yet prevalence studies indicate that by age 70, virtually 100% of our patients carry significant numbers of them in the lashes.1
How and why have we been missing this for so long? Recently, much more attention has been given to this tiny creature and the contributory role it may play in just about every form of ocular surface disease-pterygium,2 ocular rosacea, allergy, and meibomian gland dysfunction (MGD),3 to name but a few. On the opposite side of the argument is that a large number of patients present without significant symptoms, with the thought process being that it is an entity that can be dismissed. As a clinician who has a passion for ocular surface disease, the fact we may have been overlooking a potential piece of the ocular surface puzzle is amazing, demonstrating to me that there is still much opportunity to learn how all of these entities interact.
I have been baffled at the sheer number of patients in my clinic who have large infestations of this tiny mite. I have been pleased when we are able to minimize their level of infestation, and often their ocular surface health indicators, both symptoms and objective signs, seem to improve as well. Like many ocular surface patients, Demodex patients often present without symptoms, most likely due to damage to the nerves that conduct signals or simple adaptation to the constant irritation. Just as in dry eye and MGD, symptoms alone are not necessarily the best means to diagnose the problem and shouldn’t preclude these patients from treatment.
5 clinical clues
How do we best diagnose the presence of Demodex? There are several clinical signs that can alert us to the presence of Demodex in the lashes, and if we are aware of these clues, we can then perform one of two simple examination techniques that will confirm the presence of the mites and help us determine the best course of action.
1. Cylindrical dandruff (CD). This is the most obvious clinical sign and is the best indicator for mite infestation. Cylindrical dandruff is visible at the slit lamp, and it is different than the scaly, scurf-like debris seen with traditional anterior blepharitis. CD is a type of debris that tends to appear more waxy, similar to dripping candle wax. It forms a sheath on the lower portion of the lash as the lash emerges from the follicle and can be a millimeter or longer in length. It tends to be most pronounced on the lashes of the upper lid, but it may be found on the lashes of the lower lid as well. When present, it is nearly pathognomonic for Demodex infestation.4
2. Alterations of the skin surrounding the lash follicle. The skin near the opening of the follicle becomes distended and rises up, looking much like a pyramid. Also, there may be a greasy, oily appearance to the skin surrounding the follicle.1
3. Changes in lash appearance. In longstanding infestations, the lashes become thin and brittle, or they may begin to lose their color. Occasionally we may see misdirection and loss of lashes,5 which likely is the result of longstanding infestation and the effects of inflammatory damage to the structure of the lash follicle.
4. Lid hyperemia/telangiectasia. Because the presence of mites is associated with increases in interleukins and different types of pro-inflammatory cytokines,6 we can see increases in levels of lid inflammation as well. This may lead to increased vascularization along the lid margin.
5. Patient history/associations with other disease. Prevalence of Demodex increases with age. Systemically, we see a very strong association in patients with acne rosacea, seborrheic dermatitis, and other forms of inflammatory skin conditions,7 as well as diabetes.8,9 There is also an association symptomatically with allergic symptoms such as itching.10
Confirming mite presence
Those are the clinical signs that can alert us to the presence of Demodex overpopulation. However, each of these items is not truly diagnostic in its own right-with the possible exception of cylindrical dandruff. Confirmation of the presence of mites, as well as establishing a means of categorizing the degree of mite infestation, can be done through one of two simple steps:
• Lash epilation. This method involves removal of a lash from the lid along with any associated debris/cylindrical dandruff and viewing the complex under a light microscope. Lash selection is important because the number of mites may vary between adjacent follicles. Choose lashes which have a fair amount of CD visible at the base, and I tend to choose those lashes which are slightly thinned relative to the average lash. Many mites (mostly dead, but some live) may also be found within the CD debris, so it can be productive to look at that as well. Lash epilation is relatively easy to do, but there is a good possibility that several mites may be left behind in the follicle. However, most studies involving Demodex utilize this method, typically examining between two and four different lashes per lid.11
• Lash rotation. This method, first described by Mastrota,12 involves using a forceps to pinch a lash a few millimeters above the base of the follicle. Keep the lash follicle as the centerpoint, and use a combination of a gentle pull and rotation of the lash around the follicle like the hands of a clock. After a few turns, oily debris and mite tails will begin to emerge out of the follicle. This debris can also be transferred to a slide and examined under a light microscope, but is easy to visualize under high magnification at the slit lamp (25-40x). The technique of lash rotation is slightly more difficult to master; however, in a busy clinic it is more efficient to perform than lash epilation, and is my preferred method. The major drawback is if a lot of debris is exuded from the follicle, it may be more difficult to visualize all of the mites to get an accurate count.
While minimizing Demodex mite populations on the lids will likely not solve all forms of ocular surface disease, decreasing their ability to contribute toward a pro-inflammatory environment of the lids would logically carry benefit for patients and aid in any concurrent treatments. As clinicians, our primary goal should be to identify pathology and provide treatment, helping ensure that our patient’s visual systems continue to function at the highest level possible for as long as we can keep it there. Eliminating parasitic overpopulation in the lids and lashes decreases inflammation and provides a healthier environment for the ocular surface to function at its best.ODT
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