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BLOG: Explaining tearing in dry eye
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In a recent OSN column, “SkyVision enters age of LipiFlow,” I was in a confessional mode. As long as that’s the case, I suppose I should just run with it. I confess, I am finding and actually reading more and more dry eye/ocular surface disease articles in honest-to-goodness scientific journals. Seriously, I almost don’t know who I am anymore.
The latest is in Ophthalmology by Arita and colleagues, and it may provide the answer to two perplexing questions we all have faced, one age-old and the other rather new. Why do dry eye patients tear? Why do symptomatic dry eye patients sometimes have a low tear osmolarity? Indeed, the title of the article pretty much tells the tale: “Increased tear fluid production as a compensatory response to meibomian gland loss.” This is a very nice companion piece to Dr. Lindstrom’s thoughts on meibomian gland dysfunction (MGD) in the June 10 edition of OSN.
The authors compare patients with aqueous deficient dry eye with those having MGD. Not surprisingly, both groups had very similar symptom severity or load, while differing significantly in clinical signs. Tear secretion in the MGD group was inversely proportional to the degree of meibomian gland loss. In other words, the fewer healthy meibomian glands documented, the greater the amount of tear production measured. This explains not only the paradoxical tearing with the dysfunctional tear variety of dry eye, but also the suppression of this symptom by treating tearing with artificial tears.
This would also explain why we often see a low tear osmolarity in patients who clearly have dry eye symptoms. Dr. Michael Lemp v1.0 ca. 2009 said this was due to “reflex tearing” that diluted the tears, lowering osmolarity. Arita and colleagues confirm Dr. Lemp’s conjecture. Dr. Lemp v2.0 ca. 2014 (quoted by Dr. Lindstrom) states that 87% of dry eye is associated with MGD. Not surprising in light of that number, tearing is a rather common symptom in dry eye patients.
Simply put, the dry eye produces more of whatever it can to make up for that which it can’t.
Disclosure: White reports he is a consultant for Bausch + Lomb, Allergan, Shire and Eyemaginations and on the speakers board for Bausch + Lomb and Allergan.