Long-term studies of Demodex and its role in chronic blepharits have been carried out in recent years. Demodex are intradermal parasites that thrive in hair follicles, meibomian and sebaceous glands. Demodex is spread through direct contact and probably by dust that contains eggs.
Demodex folliculorum is the tiny parasitic mite that lives primarily in eyelash follicles and the meibomian glands. Demodex brevis mites live primarily in sebaceous glands connected to hair follicles and the glands of Zeis. These mites are now linked to some forms of rosacea. Both species are primarily found in the face, near the nose, the eyelashes and eyebrows.
The Demodex mites try to avoid light. Mating takes place in hair follicle openings at night and eggs are often laid deep inside the sebaceous and meibomian glands. The larvae hatch in the glands after 3-4 days, and it takes about seven days for the larvae to develop into adults that venture out at night.
In the vast majority of cases, Demodex mites go unobserved, without any adverse symptoms. However, in some people with suppressed immune systems, mite populations can dramatically increase, resulting in a condition know as demodicosis. The symptoms include ocular irritation including dry eyes, itching, scaling of lids, decreased vision and madarosis (loss of lashes).
It is now thought that pathological changes in the course of demodicosis of the eyelids are consequences of:
- Blockage of follicles, and by reactive hyperkeratinization and epithelial hyperplasia
- A mechanical vector role of bacteria
- Host’s inflammatory reaction to the presence of parasite’s chitine (a long-chain polysaccharide that serves as an armor or cell wall for fungi and parasites)
- Stimulation of the host’s humoral responses and cell-mediated immunological reactions under the influence of the mites and their waste products
- Increased age – demodicosis may be the result of age-related decrease of immunity
It has been speculated that a large amount of blepharitis (meibomian gland inflammation) associated dry eye disease, as well as ocular surface and conjunctival inflammation, could be caused by infestation of Demodex mites. This infestation interferes with meibomian gland lipid (oil) output, which is necessary to hold lacrimal gland liquid (water) output on the ocular surface.
Demodex infestation can also lead to corneal manifestations including superficial corneal vascularization, marginal corneal infiltration, superficial corneal opacity and nodular corneal scaring.
One study of 435 people examined eyelashes from people aged 2 to 96 years. Samples of the eyelashes were removed from each subject and studied under a light microscope. Infection of Demodex was classified on the basis of presence of mature and larval forms, and after observing chitinous exuviae affixed to the subjects eyelashes.
This study concluded that Demodex occures among:
- 13% of subject aged 3 to 15 years
- 34% of subjects aged 19 to 25 years
- 69% of subjects aged 31 to 50 years
- 87% of subjects aged 51 to 70 years
- 95% of subjects aged 71-96 years
Treatment of demodicosis of the eyelids can last for months. It includes tea tree oil, yellow mercurial ointment, sulphur ointment, camphorated oil, steroids, antibiotics and metronidazole gel or ointment.
Prevention: Many attribute tear function and ocular surface improvements to suppression of inflammatory mediators by the iron-binding protein, lactoferrin. Through its unique combination of antimicrobial action and anti-inflammatory activities, lactoferrin in the tear film provides a protective effect against a large variety of microorganisms including parasites, bacteria, viruses, and fungi.
Lactoferrin is produced by neutrophils, lacrimal glands, ocular surface epithelial cells, and meibomian glands. Lactoferrin has been suggested to dampen the complement activation pathway by binding to markers of inflammation (think Il-1 and Il-6), while pathogen-associated molecular patterns, such as lipopolysaccharides are targeted by lactoferrin for removal through tears and hydrodynamic flushing.
From Friday Pearls Ellen Troyer, MT MA Biosyntrx Chief Research Officer