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    What’s all the craze about demodex?

    Alleviate confusion on prevalence, morbidity, and treatment

    While many eyecare practitioners (ECPs) are just now learning about demodex infestation of the eyelids and adnexa, the fact is that this condition has been around for as long as mankind. The entomologists Johannsen and Riley from Cornell University first described the species in detail anatomically as early as 1915,1 but it wasn’t until the 1960s that clinical reports of demodex-related blepharitis began to emerge in the literature.2

    Yet this common condition largely flew under the radar in terms of clinical recognition despite its ubiquitous nature and nebulous but certain contributor to ocular surface inflammation and disease. The craze of ECPs diagnosing and treating demodex-related blepharitis has a lot of “craze” to it—there are many misperceptions out there from prevalence to morbidity, treatment, and beyond. Here, we will review the current thinking around this hysterical phenomenon.

    Related: A different approach to treating demodex blepharitis 

    Two types of Demodex

    Demodex mites are microscopic ectoparasites found in human skin. They are extremely common, and their rate of infestation increases with age. The life span of demodex outside the living body is very limited. Direct contact is thought to be required for transmission of the mites. The lifecycle of demodex from egg/molt to an adult is quite short and no longer than two to three weeks. The adult stage is less than a week, and this is when mating occurs.

    There has been much discussion about the means of mating for demodex, from mass reproduction on the host eyelid during sleep to microscopic size differences in genitalia.3 The fact is, demodex are proficient and efficient at reproducing. What it isn’t well understood is why so many people don’t have symptoms of obvious clinical demodex.

    There are two species: Demodex folliculorum and Demodex brevis. D. folliculorum involves infestation of the hair follicles, most commonly the eyelash follicle. This type can also be found in adnexal infestations involving the small hair follicles around the eye and face. Anatomically, D. folliculorum is longer and thinner than its brother D. brevis.

    D. brevis prefers sebaceous glands of the face as well as the meibomian glands. Sebum (and presumably meibum) is the main food source for the brevis variety. D. brevis has been implicated as a causative factor in several subtypes of rosacea.4 Indeed, rosacea affects the same sebaceous glands that brevis like so well. Demodex have been implicated as the cause of many other dermatological conditions including perioral dermatitis.5

    Next: Demodex and ocular involvement

    Ben Gaddie, OD, FAAO
    Dr. Gaddie is the owner and director of Gaddie Eye Centers, a multi-location, full-service practice in Louisville, KY. He is a Fellow of ...


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