At the completion of this CPD activity, optometrists will understand the clinical aspects Demodex infestation. Including: 

Many patients are surprised to learn their red, uncomfortable eyes could be caused by a species of parasites living on their eyelids. DR MARIA MARKOULLI and ZAHRA TAJBAKHSH explore the clinical implication of Demodex infestation. They provide an overview of the condition, clinical management strategies, and patient education tips to encourage understanding and compliance.  

Zahra Tajbakhsh Optom MSc PhD candidate School of Optometry and Vision Science, UNSW Sydney A/Prof Maria Markoulli PhD MOptom GradCertOcTher FBCLA FAAO Associate Professor | Postgraduate Research Coordinator | Academic lead UNSW Dry Eye clinic | School of Optometry and Vision Science Deputy Editor | Clinical and Experimental Optometry Board Member | The Optical Foundation TFOS Ambassador 

Co lourless, hairless and cylindrical-shaped, Demodex mites are the most common ectoparasite in humans. They are extremely small (0.15 mm – 0.4 mm), and, despite their eight legs, they have limited motility. 

Two species of Demodex have been identified in humans: Demodex folliculorum (D. folliculorum) and Demodex brevis (D. brevis). 

D.folliculorum gather in clusters in the superficial structures of the follicles of the eyelashes – they tend to be larger than D. brevis, which reside alone, anchored deeper in the sebaceous glands.1 

Sensitive to light, Demodex mites are more mobile in a dark environment. They are also host-dependent and can survive only a few days ex-vivo. The complete life cycle of each mite is about 15 days, after which the mite bursts and spills its contents into the surrounding tissue. 

Demodex can be both commensal and opportunistic. As commensal organisms, they have a symbiotic relationship with humans without causing any harm to their host. However, they have the potential to change their role from ‘commensals’ to ‘parasites’ if the host’s skin environment facilitates their proliferation.2 

Once the population of Demodex mites on the skin exceeds a critical level, they can become pathogenic, known as ‘demodicosis’.2 Demodicosis can affect the facial skin as well as eyelids. In a study of participants with Demodex blepharitis, a high density of Demodex mites in the facial skin was also found.3 Demodex can also play a role in pterygium or exacerbate pre-existing dry eye.4,5 Daily personal hygiene is not helpful in treating ocular Demodex as it is difficult to reach them because of the deep-set position of eye and eyelid margin.  

Interestingly, Demodex mites are not found in the skin of newborn infants; however, they can be found later in childhood – likely due to transmission from family members. Generally, there is a lower risk of Demodex infestation in children, possibly due to their lower level of sebaceous gland secretions, which result in fewer secretions for the mites.

Demodex mites and associated factors

The prevalence of ocular Demodex has been reported to range between 14% to 89% in different populations with an increased prevalence with age, dermatological conditions and systemic diseases without any difference between genders.6 

Depending on the Demodex infection type (D. folliculorum or D. brevis type), the eyelid appearance and severity can be different. When meibomian gland dysfunction (MGD) and chalazia are present, an overpopulation of D. brevis in the meibomian gland can be observed. 

D. folliculorum can be seen in 90% of anterior blepharitis and 60-88% of MGD cases.7,8 This is because of the close proximity of eyelash follicles to the meibomian glands which can affect one another.

There are several associated factors that facilitate the proliferation of Demodex including acne rosacea, leukemia, HIV infection and AIDS, immunosuppression medication, chemotherapy, phototherapy, and chronic dialysis.2,9 Predisposing factors such as contact lens wear, depression, emotional stress, malnutrition, sleep deprivation and skin tumours also have an effect.10,11

Notably, because the concomitance of facial and palpebral Demodex infestation has been reported in patients with Demodex blepharitis,3  a co-management approach between eyecare professionals and dermatologists is important in order to successfully manage both the ocular and facial forms of this condition. 

Cylindrical dandruff at the base of the eyelash is the main clinical presentation of Demodex.12 In order to observe an individual mite in the clinical setting using a slit-lamp, the lash can be rotated at its base several times using tweezers, (termed the ‘Mastrota rotation’) until its tail emerges partially from the follicle. Another method is to exert ‘lateral tension’ on the lash to observe the emerging tail from the follicle opening without lash epilation.13

Lash epilation and in-vivo confocal microscopy are two research techniques used to count Demodex. In-vivo confocal microscopy involves applying the probe of the instrument to the eyelid margin. It provides complete observation of the lash contents, without the need to epilate the lash.10 In the lash epilation method, a lash with cylindrical dandruff is epilated and observed under a microscope for the quantification of the mites attached to it. Both techniques are restricted to the research setting and are influenced by the lash chosen for observation, hence yielding variable results.14 

Clinical presentation of ocular Demodex

The clinical presentation includes itching, especially along the lid margin, swollen eyelids, and ocular discomfort, symptoms typical of blepharitis. Cylindrical dandruff surrounding the base of the lash are pathognomonic of ocular Demodex. Some patients may present with loose lashes, and misdirected lashes or trichiasis due to Demodex infestation that impact nutrients and follicle structure.6 In more severe cases, Demodex can block the openings of follicles and gland ducts, leading to epithelial hyperplasia and hyperkeratinisation.  

It is important to manage Demodex to prevent contact lens discomfort and dropout. There has been a positive correlation between the presence of Demodex and intolerance to contact lens wear.15 Contact lenses may encourage microorganism accumulation, which provides a more favourable environment for Demodex proliferation.  

The aim of management of Demodex is not to eradicate the mites, but rather to reduce their population in order to restore normal ocular surface ecology. There are several management options for Demodex infestation: 

1. Lid scrubs containing tea tree oil (TTO)

2. Combined therapy of both high concentration TTO in-office and exfoliation, and at-home therapy 

The recommended duration of treatment is for at least two Demodex mite lifecycles. Considering each mite lifecycle is approximately 15 days, a duration of 4-6 weeks of treatment is recommended. 

Tee tree oil (TTO) is an essential oil derived from the leaves of a small tree known as Australian Melaleuca alternifolia. It is used topically, applied directly to the eyelid and lash follicles, and it is highly toxic if ingested. Terpinene-4-ol (T40) is the most active TTO molecular compound against Demodex mites (an ingredient found in many lid wipes). 

The full mechanism of TTO against Demodex remains largely unknown, however, it is thought that TTO encourages the Demodex mites to migrate out of the follicle, enabling better access for lid wipes and other forms of therapy. 

Hygiene products and delivery mechanisms

We have a range of products available to us now for the management of eyelid disease. Despite the range, they have certain key ingredients in common: most contain mild cleansing surfactants and antimicrobial ingredients. Many also contain TTO. A variety of delivery mechanisms of these products are available, including wipes, pumps, gels and sprays. It is not clear which of these mechanisms is superior and there are no studies on the optimal regimen (once versus twice a day), technique and duration of the procedure (5, 10 or 15 minutes) for eyelid hygiene.  

Each delivery mechanism has its own pros and cons. 

Wipes – these are single-use and sterile which limits cross-contamination. The application involves gentle pressure along the lash line. Patients need to be trained in-office on how to apply wipes as forceful rubbing may irritate the delicate eyelid skin. In-office education and trial are recommended so that the patient can be warned to expect a cooling or burning sensation. (It is reported that a pre-soaked wipe with T40 can cause ‘transient discomfort’).16 

In a study that applied a type of T40 wipe twice a day, signs and symptoms of blepharitis significantly decreased with a reduction of debris along the lash line, and an improvement in meibum quality.17

Pumps – Some patients prefer the pump delivery system. Pumps deliver the product as a foam, cream or liquid which then needs to be rinsed off the eyelid. Foam eyelid cleanser containing TTO and linalool was found to be more effective at alleviating both the signs and symptoms related to ocular surface inflammation over baby shampoo.18 Other studies have shown that this delivery mechanism can improve tear break up time, decrease meibomian gland obstruction and, despite variable compliance, it’s well-tolerated by patients.19,20 

Gels – An advantage of gels over other delivery mechanisms is that the gel formulation reduces the degree of friction on the sensitive eyelid skin compared to wipes, and 85% of patients have rated this delivery mechanism as acceptable.21 Gel formulations are applied to the fingertips and, similar to pumps, patients need to be educated regarding proper hand hygiene prior to the use of gel.

Sprays – Relatively new to the market, sprays are either applied directly to the eyelid or to a cotton pad and then rubbed onto the closed eyelids, with no need to rinse. This delivery mechanism is well tolerated by patients.20 A significant reduction in the overall bacterial load, especially S.epidermidis has been reported, however there is no report about the efficacy of sprays on Demodex as yet.22 

Although the majority of the aforementioned products are well-tolerated, each of these products would benefit from demonstration and trial in the clinic. Demonstrations will help set patient expectations regarding any possible transient discomfort that they might experience, and provide clarification as to precisely how the product should be applied to the eyelid, including location, amount of pressure and necessary hand hygiene. 

Warm compresses and their effect on ocular Demodex – Eyecare practitioners often recommend lid hygiene along with the use of a warm compress, especially for the management of meibomian gland dysfunction. An obvious question is whether these warm compresses are beneficial or detrimental in the management of Demodex. 

Both D. brevis and D. folliculorum prefer lower temperatures, and temperatures above 37°C are damaging, especially for D. folliculorum,9 with the higher temperature eventually paralysing the D. folliculorum’s nervous system.

One study investigated the efficacy of warm compress on Demodex infestation using three devices: a face cloth, the MGDRx eyebag (The EyeBag Company, Halifax, UK) and OPTASE moist heat mask (Scope Ophthalmics Ltd., Dublin, Ireland), over a period of eight weeks. The quantity of Demodex decreased significantly in the group using the OPTASE moist heat mask. While the MGDRx eyebag did not appear to have a significant impact on Demodex quantity, the proportion of Demodex infestation improved significantly by 25 per cent, which suggests that heat may be an important addition to managing Demodex.23 

Intense pulsed light (IPL) – Recently, IPL has been recommended as an in-office treatment for Demodex infestation. In a 2019 study, 40 patients were treated with either 5% TTO or IPL over a three-month period.24 Compared with the TTO group, the IPL group had faster improvement. The average number of Demodex decreased significantly after both one and three months of IPL and the overall Demodex eradication rate was 100% compared to 75% for the TTO group. 

These results suggest that IPL treatment is efficacious in eradicating Demodex, and patients may accept it more readily since it takes effect more quickly, with minimal effort on their part. A possible mechanism of IPL is that the light produced by the IPL is directed to the skin tissue and absorbed, resulting in the production of heat, which eliminate mites effectively.24 

Manuka honey – Topical use of manuka honey has been recently proposed for Demodex treatment. In a clinical trial study, 53 participants with blepharitis were randomly assigned to apply manuka honey microemulsion eye cream to one eye, with the other eye serving as the control eye. After three months of therapy, the eyes treated with manuka honey had a significant decrease in Demodex infestation compared to the control eye. Several factors may attribute to the clinical efficacy of manuka honey, including the established antibacterial, anti-Demodex, and anti-inflammatory properties of manuka honey.25

Micro-blepharoexfoliation – The BlephEx is a device, which consists of a hand-held electromechanical unit and a disposable micro-sponge that spins rapidly to provide debridement and exfoliation at the lash margin. For the purpose of Demodex blepharitis treatment, the sponge is soaked in a lid-cleaning solution, such as TTO, and then applied to the lid margin for approximately 20-30 seconds. The aim is to remove as much debris as possible, and to debride the lid margin. The eyes are rinsed with saline at the end to remove any debris or solution. 

The in-house use of this method has been shown to give a greater improvement in symptoms and has been recommended as a starting point in the management of blepharitis.