Pathogenic role of Demodex mites in blepharitis

Abstract

Purpose of review: To summarize the key literature and our research experience regarding Demodex infestation as a potential cause of ocular inflammatory diseases with a special emphasis on Demodex blepharitis.

Recent findings: Two distinct Demodex species have been confirmed as a cause of blepharitis: Demodex folliculorum can cause anterior blepharitis associated with disorders of eyelashes, and D. brevis can cause posterior blepharitis with meibomian gland dysfunction and keratoconjunctivitis. Tea tree oil treatments with either 50% lid scrubs or 5% lid massages are effective in eradicating mites and reducing ocular surface inflammation.

Summary: Demodex blepharitis is a common but overlooked external eye disease. The pathogenesis of Demodex blepharitis in eliciting ocular surface inflammation has been further clarified. The modified eyelash sampling and counting method makes it easier and more accurate to diagnose Demodex infestation. Tea tree oil shows promising potential to treat Demodex blepharitis by reducing Demodex counts with additional antibacterial, antifungal, and anti-inflammatory actions.

Figures

Figure 1. Microscopic photograph of Demodex mites

Demodex folliculorum (a), Demodex brevis (b), Demodex larva with three pairs of poorly developed legs (c) and Demodex egg (d).

Figure 2. Ocular manifestations of Demodex infestation

Photographs demonstrating the typical cylindrical dundraff at the root of the eyelashes (a, red arrow); misdirected lashes (b, blue arrow); meibomian gland dysfunction (c, green arrow); lid margin inflammation (d, black arrow); bulbar conjunctiva inflammation (e); corneal infiltration and pannus (f, yellow arrow).

Figure 3. Microscopic examination of lashes

Obscured Demodex mites in a compact dandruff (a, green arrows) were easily detected after adding 0.25% fluorescein solution (b, blue arrows). Reproduced from [28].

Figure 4. Photographs before and after TTO treatments

Cylindrical dandruff (a), lid margin inflammation and bulbar conjunctival injection (b) and marginal corneal vascularization (c; yellow arrows) were resolved with TTO regimen (d–f), respectively. Reproduced from [25].