Study Shows Clinical Utility of Demodex Mite Per Lash Measurement

Color enhanced image of a hair follicle mite (Demodex folliculorum) of a human. The mites, less than 0.4mm long, can be found in small hair follicles and eyelash follicles. They live head down in a follicle and are relatively harmless. Large numbers of demodex mites, though, can cause itching and skin disorders (Demodicosis). Enhancement of 9b2165.
Researchers offer guidance on managing, not completely exterminating, the last mites.

Decreasing Demodex count per lash, rather than total extermination of Demodex, may be a realistic clinical goal when treating patients with a Demodex infestation, according to a research letter published in Eye. 

Demodex infestation due to Demodex folliculorum or Demodex brevis is frequently underdiagnosed, and previous research has focused on total Demodex count as a measure of clinical improvement. In this study, researchers sought to evaluate the utility of Demodex mite count per lash, rather than total mite count, to determine the effect of tea tree oil treatment with clinical improvement in infection symptoms and signs. 

A total of 94 eyes in 47 patients (78.7% women; mean age, 65.97 years ± 12.62 years) were treated with 50% tea tree oil therapy under topical anesthesia in a clinical setting and 5% tea tree oil treatment twice daily at home. Participants were evaluated every 2 weeks for a 1-month period. 

At each follow-up visit, 3 lashes were removed from each eye. Investigators calculated Demodex count per lash using a light microscope, and graded lid margin abnormalities via the meibomian gland dysfunction/lid margin grading scale. Basal Schirmer and tear film break-up time tests were also performed. 

Within the cohort, the most commonly reported symptoms prior to treatment included discharge and itching, seen in 89.4% and 93% of patients, respectively, with itching reported as the most severe symptom. Following treatment, itching was still the most commonly reported, most severe symptom. 

Investigators observed significant improvements in itching, foreign body sensation, discharge, dryness, and lid margin crusting, and Demodex count per lash decreased significantly from 1.24 to 0.69 mites per lash (P =.00). Significant improvements were also seen in total lid margin score and meibomian gland plugging and thickening. Tear film break-up time significantly increased following the treatment regimen. 

Researchers conducted a multiple regression analysis adjusted for both age and sex. Findings of this analysis demonstrated that tea tree oil treatment “significantly improved” itching, foreign body sensation, discharge, and lash dandruff, which correlated with a decrease of roughly 0.63 Demodex per lash (P =.01). 

The researchers propose that “a change of about 1 mite/lash may be a clinical standard for improvement. Treatment of Demodex should require both the patient’s and clinician’s long-term dedication and persistence to keep Demodex count/lash down.” 


Lo K-S, Xie A, Yang JJ, Shen EP. Critical value of Demodex count per lash for symptomatic and clinical improvement of Demodex blepharitis. Published online February 19, 2021. Eye. doi:10.1038/s41433-021-01442-z