Douglas K Devries, OD, illustrates the current prevalence of patients diagnosed with Demodex blepharitis.
Douglas K. Devries, OD: I’ve been aware of the prevalence of Demodex blepharitis for years. As I studied patients with dry eye and I was looking for underlying causes, I began to look at some of the research, and I was astounded by some of the early research. One particular paper out of the UK said that as somebody got into their sixth or seventh decade, [prevalance] could be as high as 85% or 90%. I started looking for Demodex blepharitis on a regular basis, and I found this tremendous prevalence. There are certain factors that we look at, which we’ll discuss as well.
When we examine the pathophysiology of Demodex blepharitis, it’s a mite. It’s a parasite. We tend to find a prevalence in patients with ocular rosacea. Patients with ocular or facial rosacea tend to be lighter-skinned, such as a Fitzpatrick type 1, type 2, or perhaps type 3. A lot of times, we find that it tends to be much more prevalent in individuals who are of Irish, English, or Scottish descent. How it presents when a patient becomes symptomatic is that these little mites in the eyelashes begin to proliferate. In some individuals, they proliferate because it’s the right physiologic environment to do so. Typically, a mite needs a food source. When we have a food source, such as polysaccharides from biofilm, they tend to start growing in numbers.
Many individuals have Demodex—not necessarily the blepharitis—but they aren’t symptomatic. But when the right physiologic environment gets set up—in other words, the polysaccharides—we see them increase in numbers. It’s very interesting with patients. They’ll want to scratch their eyelash margin. It isn’t an itch like you’d find in an allergic reaction. They’re very specific with where they’re bothered. The reason that they’re bothered and wanting to scratch the eyelash margin is because as those Demodex blepharitis proliferate, they release exotoxins. The exotoxins then have this whole reaction with the body in which the individual becomes inflamed and the eyelid margins become inflamed and thicken, so they want to scratch that. The pathophysiology dictates that it’s going to create additional inflammation on those patients. In those patients with dry eye, that’s 1 more source of inflammation that’s going to cause the patient discomfort.
Transcript edited for clarity.