Demodex mites frequently inhabit human hair follicles, and an over-abundance of them tends to be associated with risk factors such as smoking, obesity, malignancy, diabetes mellitus and AIDS—all related to impaired immunity, in addition to immunomodulatory medications. Studies have also noted that demodicosis may have a genetic component.
Ocular demodicosis tends to be age-dependent and linked to anterior blepharitis, meibomian gland dysfunction, chalazia and keratoconjunctivitis. To better understand the impact Demodex has on dry eye patients, a recent study evaluated Demodex in relation to a number of ocular surface parameters.
The cross-sectional study consisted of 119 individuals with dry eye symptoms from the Miami Veterans Administration Medical Center, grouped by presence of ocular demodicosis. Each participant filled out a questionnaire and underwent an ocular surface examination.
The researchers noted that Demodex was highly prevalent in the study population, affecting almost 70%. Regardless of the presence of Demodex, all participants had comparable demographics and symptom profiles, as recorded on the Dry Eye Questionnaire 5 and Ocular Surface Disease Index, as well as similar tear production and corneal staining. However, those with Demodex were far more likely to report itching (58.5% vs. 35.1%), with increasing frequency of itching with higher Demodex counts. Those with Demodex also had more severe eyelid abnormalities, such as cylindrical dandruff and lid vascularity, and a more unstable tear film, but neither Demodex nor ocular surface findings related to dry eye symptoms.
The researchers concluded that Demodex is highly prevalent in older populations with dry eye. They wrote that itching and cylindrical dandruff were the findings most specific for Demodex.
Cheng AM, Hwang J, Dermer H and Galor A. Prevalence of ocular demodicosis in an older population and its association with symptoms and signs of dry eye. Cornea. 2020:1-7.