Demodex Blepharitis 101
What is Demodex?
Demodex is a mite. A mite is a living, moving organism. Mites are cousins to spiders and ticks. They live in hair follicles and in oil glands. Almost everyone is colonized with Demodex mites, but only rarely do the mites cause symptoms or disease.
Demodex mites are extremely small. It would take several of them to cover a pin head.
When you sleep, mites come out of follicles, mate, and then go back into the follicles to lay eggs.
How does Demodex affect the eyes?
A number of years ago Demodex was identified in the eye lash follicles of patients with blepharitis. Demodex can also live in oil glands such as Meibomian glands.
Demodex mites living in eyelash follicles generate waste products which accumulate at the base of the eyelashes, in a characteristic pattern called collarettes.
Demodex mites living in Meibomian glands generate waste products which can clog the orifices, leading to inadequate oil production.
What are the symptoms of Demodex infestation of my eyelids?
Demodex is one cause of blepharitis, both anterior blepharitis (primarily involving the eyelashes and the outer edge of the eyelid) and posterior blepharitis (primarily involving the Meibomian glands). Both types can be present at the same time.
The symptoms of Demodex are indistinguishable from symptoms of blepharitis from other causes.
How does my doctor diagnose Demodex?
Your doctor can pull several eyelashes and examine them for the presence of Demodex mites using a microscope.
In reality, this is rarely performed. Instead, your doctor suspects Demodex based on failure to respond to other treatments for blepharitis and the presence of collarettes on the eyelashes.
If I have collarettes, do I automatically need treatment for Demodex?
No. Occasional collarettes can be seen in the eyelashes of patients who do not have any symptoms of blepharitis.
If I don’t have collarettes, does this mean that I don’t have Demodex?
No.
First, if you scrub your eyelashes frequently you may be removing the collarettes.
Second, although collarettes are felt to be typical of Demodex, other kinds of build-up on the base of the eyelashes can also occur with Demodex that fall short of the appearance of collarettes.
Can I remove the Demodex with eyelid scrubs?
No. Demodex mites spend most of their time hiding inside the eyelash follicles and the Meibomian glands. You can’t scrub them out of those locations.
Excessive scrubbing to remove eyelash debris can be irritating in itself (especially if you are using a tea tree product) and will not kill the Demodex.
When should I be treated for Demodex?
The answer to this question is evolving as eye care providers expand their understanding of the role of Demodex mites in chronic blepharitis.
If you have symptomatic blepharitis and have numerous collarettes, and have never been treated for blepharitis in any way, it is reasonable to treat for Demodex mites as a first line approach at the same time that other topical treatments are begun (such as drops, ointments, and hot compresses).
If you have been treated for blepharitis using multiple modalities (heat, scrubs, topical and oral medications, devices) and nothing seems to work consistently, it is reasonable to treat for Demodex mites because until the mites are killed, you will not have long term success. This is true whether or not you have classic collarettes.
How should I be treated for Demodex?
The FDA very recently approved (July 25, 2023) an eye drop called Xdemvy for Demodex. The drop is used twice a day for 6 weeks only. It works by paralyzing the mites. Insurance coverage and cost to the patient are yet to be determined.
It is critical to understand that if you use this eye drop as directed for 6 weeks, you have gotten all the benefit you are going to get from the medication. It works by killing a living organism and it will either kill it or not kill it. Extending the treatment for 12 or 18 weeks is not indicated. Combining Xdemvy with tea tree lid scrubs is not indicated. Repeating Xdemvy if it did not help the first time is not indicated.
Remember also that unless your doctor has pulled eyelashes and confirmed that Demodex is in your lash follicles, this treatment is presumptive. You may not have Demodex. Extending or repeating treatment with a Demodex killing medication when you don’t have Demodex has no benefit.
An oral medication which is effective, cheap and readily available is ivermectin. Ivermectin has been used for decades for a wide range of parasitic diseases in humans and animals and has an excellent safety profile. It was the first oral medication attempted for treatment of Demodex blepharitis. It can be used in children for presumed Demodex blepharitis. Demodex mites also cause unpleasant skin conditions (collectively called demodicosis), and dermatologists have used oral ivermectin to treat these conditions.
Can Demodex mites come back?
Yes. Mites can travel from person to person. Local treatment with Xdemvy only eradicates mites living on the eyelids, not elsewhere on your body (skin oil glands, hair follicles).
If you are treated for Demodex and have significant relief that can be directly ascribed to the Demodex treatment (either you were not also started on numerous other blepharitis treatments, or Demodex treatment finally made you better) and months or years later your blepharitis returns or becomes difficult to control, repeat treatment for Demodex may be indicated.
If your eye care provider prescribes Xdemvy and then suggests repeating treatment in less than 1 year, consider whether you may not have Demodex at all, or whether instead you need ivermectin to decrease the overall colonization of Demodex on your skin and in your hair follicles.
Ivermectin Treatment
Ivermectin is the mainstay of the global eradication campaigns for Onchocerciasis and lymphatic Filariasis. Hundreds of millions of doses have been administered worldwide.
There is no firmly established treatment protocol for Demodex blepharitis, however a common approach is to treat with a single weight-adjusted dose of ivermectin, wait two weeks and repeat the dose (kill the adults, then kill the eggs that have hatched after the first dose).
If your doctor recommends treatment for Demodex, but you can’t afford Xdemvy, don’t hesitate to ask about ivermectin. In the US, ten 3 mg tablets of ivermectin costs less than $20.
Ivermectin 3 mg tablet dosing from the Physician’s Drug Reference:
(to convert from pounds to kg, divide your weight in pounds by 2.2)
Weight Dose
15 – 25 kg 1 tablet
26 – 44 kg 2 tablets
45 – 64 kg 3 tablets
65 – 84 kg 4 tablets
Typical schedule: one weight-adjusted dose, or two weight adjusted doses separated by 2 weeks.
For a fascinating explanation of the discovery of ivermectin and its use in combatting global scourge infections in humans and animals, see this link (it is possible to understand while skipping the science).
