Over the past decade, eyecare providers have been increasingly drawn to the presence of Demodex mites on the eyelid and lash follicles as potential contributors to a string of ocular health issues – from chronic styes to blepharitis to ocular rosacea. Current standard of care for eradicating Demodex associated blepharitis is treatment with 50% tea tree oil-based eyelid cleanser and 5% tea tree oil ointment for up to 4 weeks. “But there are almost no clinical studies looking at the impact of these treatments on the eye,” Dr. David Sullivan explains during this podcast.

Dr. David Sullivan, TFOS Founder

Dr. David Sullivan, founder of the Tear Film and Ocular Surface Society and current Chairman of the Board of Directors, is a PhD whose lab at Schepens Eye Research Institute/Harvard Medical School has brought forward many new insights into ocular surface disease treatment and management over the last 40 years. Working as a fellow in his lab, Di Chen, MD, PhD, had the idea to investigate what tea tree oil was doing to meibomian gland cells if we knew from prior research that tea tree oil had endocrine disruptive hormonal effects on human cells.  “We wanted to test if tea tree oil would have the same effect on meibomian gland cells because we know that a lot of doctors use tea tree oil products on eyelids, and we don’t know its’ effects,” Dr. Chen explains about the inspiration behind her research. “We know [tea tree oil] can kill Demodex, but we don’t know it’s effects on human cells so why don’t we test this on human meibomian gland cells. To our surprise it killed those cells.” 

Her new study demonstrates that tea tree oil at the concentrations currently used in commercially available eyelid cleansers (and even considerably lower strengths) will not only kill Demodex populations, but the healthy meibomian gland ocular tissue we are trying to preserve.

Terpinen-4-ol (T4O) is the active ingredient in tea tree oil that is most effective in killing Demodex; in vitro studies show that exposure to 1% T4O for 88 minutes or 4% T4O for 44 minutes can kill Demodex mites. In routine use today are eyelid cleansing wipes containing between 2-4% T4O for eyelid hygiene or even makeup removal. In this study, researchers tested cultured human meibomian gland epithelial cells in vitro with exposure to dose and time dependent concentrations of T4O. After just 15 minutes of exposure to 1% T4O, human meibomian gland epithelial cells exhibited cell morphology changes and atrophy, and after 90 minutes of such treatment, all cells died. At the same concentration and exposure time that it takes to kill Demodex mites, the human meibomian gland cells we are trying to “treat” with tea tree oil-based lid hygiene prescribed for posterior blepharitis or chronic styes or chalazion are also killed.

Dr. Di Chen, MD, PhD

There has been very little literature published on the effects of tea tree oil and T4O on the health of the ocular surface tissues being exposed during treatment. We do know that T4O is a small molecule that can rapidly penetrate through the skin epidermal tissue. Prior studies have demonstrated that after application of 2-4% tea tree oil ointment to the skin, tea tree oil components permeate the tissue and remain at concentrations of 0.23 – 0.37% after 24 hours. Extrapolated to eyelid skin, a concentration of 0.2% T4O for 24 hours would kill human meibomian gland cells based ...