Demodex Blepharitis: A Comprehensive Review of the Disease, Current Management, and Emerging Therapies

Demodex blepharitis is a common disease of the eyelid, affecting approximately 25 million Americans. This article reviews what is known about the mechanisms and impact of Demodex blepharitis, risk factors, signs and symptoms, diagnostic techniques, current management options, and emerging treatments. Demodex mites contribute to blepharitis in several ways: direct mechanical damage, as a vector for bacteria, and by inducing hypersensitivity and inflammation. Risk factors for Demodex blepharitis include increasing age, rosacea, and diabetes. The costs, symptom burden, and psychosocial effects of Demodex blepharitis are considerable. The presence of collarettes is pathognomonic for Demodex blepharitis. Redness, dryness, discomfort, foreign body sensation, lash anomalies, and itching are also hallmarks of the disease. Although a number of oral, topical, eyelid hygiene and device-based options have been used clinically and evaluated in studies for the management of Demodex blepharitis, none have been FDA approved to treat the disease. Recent randomized controlled clinical trials suggest that lotilaner ophthalmic solution, 0.25%, is a topical treatment with the potential to eradicate Demodex mites and eliminate collarettes and eyelid redness for an extended period.

Blepharitis is a chronic inflammation of the eyelid margin characterized by erythema, ocular irritation and discomfort, discharge and debris on the eyelids and lashes, and eyelash anomalies.1,2 In more advanced stages, there may be corneal involvement, such as punctate epithelial erosions, infiltrates, epithelial defects, or keratitis.

Although blepharitis can have various etiologies, including allergic, staphylococcal, and seborrheic, one of the most common etiologies is Demodex mite infestation.3,4 The presence of Demodex mites in eyelid tissue was first reported in 1876, and its association with blepharitis was established in 1967, but the number of published articles on Demodex blepharitis has increased dramatically in the past 5 years.5

This literature review presents the available evidence and knowledge about Demodex blepharitis. We review what is known about the epidemiology, mechanisms and impact of the disease, risk factors, signs and symptoms, diagnostic techniques, current management options, and emerging treatments.

EPIDEMIOLOGY

It has long been accepted that the prevalence of Demodex increases with age, affecting more than 80% of those older than 60 years and 100% of those older than 70 years.6 Among younger, university-based populations, Demodex prevalence has been reported as consistently low, between 2% and 27%.7–9

Researchers who have studied patient populations with clinical signs and symptoms of blepharitis find high rates of Demodex infestation, with prevalence ranging from 29% to 90%.4 Most authors in the past 5 years report that Demodex blepharitis accounts for ≥60% of those with blepharitis.3,10–13

Recently, two studies independently reported similar rates of Demodex blepharitis among patients of all ages visiting US eye care clinics.14,15 The Titan study, a multicenter retrospective chart review, found that 58% of 1,032 consecutive patients (and 69% of those with a blepharitis diagnosis) presented with collarettes—waxy, cylindrical debris at the base of the lashes that are the pathognomonic sign of Demodex blepharitis.14 Similarly, Teo et al.15 found that 55% of all patients and 62% of blepharitis patients examined in two tertiary care clinics presented with Demodex based on lash epilation.

Demodex blepharitis is equally prevalent in both sexes.10,14 Among older Americans referred to a Veterans Administration (VA) Medical Center dry eye clinic, the rate of Demodex infestation was similar regardless of ethnicity, with 72% of white patients, 65% of black patients, and 69% of Hispanic patients affected.3

MECHANISMS OF DISEASE

Demodex mites, the most common ectoparasite on humans, have been implicated in blepharitis. Two species, Demodex folliculorum and Demodex brevis, are found in human skin, especially the cheeks, nose, and eyelids. Both species are translucent, elongated microscopic mites with four pairs of short, clawed legs. Demodex folliculorum (Fig. 1) is approximately 0.3 to 0.4 mm in length and can be found in clusters around the lash root and lash follicle, where D. folliculorum feeds on sebum and follicular epithelial cells.16Demodex brevis is shorter, more solitary, and prefers sebaceous glands.16 Although Demodex mites are found on healthy, asymptomatic individuals of all ages,10 it has been suggested that the mites may play a pathogenic role at higher density, when the mites reach a state of demodicosis.16

FIG. 1.:

Demodex folliculorum is found in human skin, especially the cheeks, nose, and eyelids. Image courtesy of Patrick Vollmer, OD.

Demodex folliculorum is believed to be more active and therefore more implicated in type 1 allergic reactions.17 Researchers have surmised that male and female mites mate outside the follicles or glands, after which the female mites lay their eggs inside the hair follicles or sebaceous glands.18

Demodex mites secrete digestive enzymes onto nearby tissues to break down the epithelial cells to consume as food.16 Although it has previously been reported that digested material is retained in the gut and spilled onto surrounding tissues at the end of the life cycle,17 a recent microbiology report suggests that is not the case and that digested material may be excreted.19 The full life cycle of a mite is estimated to be from 14 to 23 days, progressing from egg to larva to nymph and finally to the adult stage.18,20

There are several plausible mechanisms by which Demodex contribute to blepharitis, including direct damage, acting as a vector for bacteria, and inducing hypersensitivity and inflammation.17,21,22 Rest of Article here: https://journals.lww.com/claojournal/fulltext/2023/08000/demodex_blepharitis__a_comprehensive_review_of_the.1.aspx