In vitro and in vivo killing of ocular Demodex by tea tree oil

Abstract

Aims: To compare the in vitro killing effect of different agents on Demodex and to report the in vivo killing effect of tea tree oil (TTO) on ocular Demodex.

Methods: Survival time of Demodex was measured under the microscope. Sampling and counting of Demodex was performed by a modified method.

Results: Demodex folliculorum survived for more than 150 minutes in 10% povidone-iodine, 75% alcohol, 50% baby shampoo, and 4% pilocarpine. However, the survival time was significantly shortened to within 15 minutes in 100% alcohol, 100% TTO, 100% caraway oil, or 100% dill weed oil. TTO's in vitro killing effect was dose dependent. Lid scrub with 50% TTO, but not with 50% baby shampoo, can further stimulate Demodex to move out to the skin. The Demodex count did not reach zero in any of the seven patients receiving daily lid scrub with baby shampoo for 40-350 days. In contrast, the Demodex count dropped to zero in seven of nine patients receiving TTO scrub in 4 weeks without recurrence.

Conclusions: Demodex is resistant to a wide range of antiseptic solutions. Weekly lid scrub with 50% TTO and daily lid scrub with tea tree shampoo is effective in eradicating ocular Demodex.

Figures

Figure 1

In vitro live and dead status of Demodex. The same Demodex was photographed before (A, C, and E) and 5 minutes later (B, D, and F). The Demodex was judged to be “live” by vivid movement of the body (A, B) or legs (C, D). In contrast, the Demodex was judged to be “dead” by the lack of movement (E, F). Furthermore, all eight legs of the dead mite were stretched apart (E, F) distinctively different from the live one (C, D).

Figure 2

Demodex counts in patients receiving lid scrub by diluted baby shampoo. In these seven patients, their serial Demodex counts did not drop to zero despite daily lid scrub with diluted baby shampoo when practised for more than 1 month. Cases 3, 4, and 5 maintained a constant Demodex count around 7–10 after 40–350 days of lid scrub. Cases 1 and 7 had an increase of Demodex count after 110 and 350 days of lid scrub. Cases 2 and 6 showed a decrease of Demodex count after 64 and 125 days of lid hygiene, respectively, but did not reach zero.

Figure 3

Different results of lid scrub by TTO and baby shampoo. In a patient presenting with symmetrical signs of CD in both eyelids, lid scrub was performed in the office by 50% TTO in the right eye (A) and by 50% baby shampoo in the left eye (B). In either eye, CD was clean after scrub (C, D), however, Demodex could be found on the lid margin adjacent to the lashes (C, arrows), and a Demodex tail could be visualised protruding from the lash root (C, arrowheads) after TTO scrub. These findings were not detected in the eye after baby shampoo scrub although the skin surface was less red (D).

Figure 4

Migration of Demodex by lid scrub with TTO. In this eye with diffuse CD found in the lashes before treatment (A), the lash to be epilated (marked by arrow) showed a fragment of CD attached to the lash and abundant Demodex embedded close to the lash follicle (D). After office lid scrub with 50% TTO, the lashes became clean, and totally free of CD, but tails of Demodex were protruding from the lash roots (B, arrow). Three minutes after lid scrub, free Demodex were found on the trunk close to the skin surface—that is, away from the lash follicle in the epilated lash (E). Rotating these lashes (shown in B) before epilation allowed us to detect a group of Demodex migrating along the lash trunk (F and G). If no lid scrub was carried out at home for 1 week, CD returned to the lashes 1 week later (C).

Figure 5

Demodex counts in patients receiving lid scrub with TTO. In these nine patients who received weekly TTO lid scrub plus daily lid scrub with TT shampoo, the Demodex counts dropped sharply in the first week after TTO treatment for all patients. Demodex counts drop to zero in 3 weeks for five patients and in 4 weeks in another two patients, but did not reach zero in two patients at day 35 and day 63.