Ocular Demodicosis as a Potential Cause of Ocular Surface Inflammation

Abstract

Among different species of mites, Demodex folliculorum and Demodex brevis are the only 2 that affect the human eye. Because demodicosis is highly age-dependent and can be found in asymptomatic adults, the pathogenicity of these mites has long been debated. In this study, we summarize our research experience including our most recent study regarding Demodex infestation as a potential cause of ocular inflammatory diseases. Specifically, we describe the pathogenesis of demodicosis and then discuss the results of work investigating the associations and relationships between ocular demodicosis and blepharitis, meibomian gland diseases, and keratitis, in turn. This is followed by some discussion of the diagnosis of demodicosis and concludes with a brief discussion of evidence for different treatments for ocular demodicosis. Collectively, our studies suggest a strong correlation between ocular demodicosis and ocular surface inflammatory conditions, such as blepharitis, chalazia, meibomian gland dysfunction, and keratitis. Further investigation of the underlying pathogenic mechanism is warranted.

Figure 1

Microscopic features of D. folliculorum (A) and D. brevis (B). These obligate mites are transparent, elongated in shape, and divided into head-neck and body-tail parts, with eight short legs attached to the former body segment. The head-body ratio is 1:2 to 1:4 for D. folliculorum, but close to 1:1 for D. brevis.

Figure 2

Slit-lamp photographs of a case with demodicosis and blepharoconjunctivitis. A 23-year-old female presented with itching in both eyes for 6 years. Four D. folliculorum mites were detected by eyelash sampling. Cylindrical dandruff (CD) was present around the eyelash roots (A, B). Follicular reaction was predominant (B). After a TTO eyelid scrub, with reduction in the Demodex count, the symptoms were relieved and the CD and the conjunctival follicles disappeared (C, D).

Figure 3

A case with ocular demodicosis and MGD. A 16-year-old female complained of irritation and dryness in both eyes for 4 years. She also had a past history of chalazia in both eyes. Two D. folliculorum and two D. brevis mites were detected. Slit-lamp examination revealed irregular, thickened, and inflamed eyelid margins and conjunctival injection in both eyes (A, B). Meibography showed meibomian gland dropout in both eyes (C, D).

Figure 4

A case with ocular demodicosis and corneal ulcer. An 18-year-old female complained of recurrent redness and irritation in her left eye for 9 years. Two years previously, she underwent penetrating keratoplasty in the left eye for corneal perforation caused by presumed herpes simplex keratitis. Two months previously, the keratitis recurred in the left eye, but failed to respond to antiviral and antibiotic regimens. Examination revealed blepharitis (A) and corneal stromal infiltration with epithelial defect and neovascularization (B). Eyelash sampling revealed two D. brevis and two D. folliculorum mites. After performing eyelid scrubs with Cliradex^® for 6 days, the ocular surface inflammation was significantly reduced (C) with healing of the corneal ulcer (D).