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    What is the coffee ring effect?

    The Line of Marx, cell physiology, and vital dyes

    I was once characterized as an “information parasite” by a colleague. I must admit that I do troll the Internet, particularly Pub Med, for new, intriguing information especially when its related to one of my two favorite ocular phenomenon that are pseudoexfoliation syndrome and the lid margin.

    Another non-sequetur confession: I am addicted to coffee. 

    More dry eye: What's all the craze about demodex?

    You can imagine my surprise, when in a Pub Med literature search, I discovered two of my favorite things, coffee and the lid margin, together, in the title of a 2016 article in Medicine. 1

    I know that you too find it hard to believe that coffee and the lid margin can be connected, however they certainly are in “‘Coffee Ring Effect’ in Ophthalmology: ‘Anionic Dye Deposition’ Hypothesis Explaining Normal Lid Margin Staining."

    More from Dr. Mastrota: How bacteria load creates biofilm

    The coffee ring effect

    To understand the article, I first had to understand the “coffee ring effect.” In physics, a "coffee ring" is a pattern left by a puddle of particle-laden liquid after it evaporates, as a droplet of coffee would. The edges of a coffee (or water) drop sitting on a table or a piece of paper, for example, are often “pinned” to the surface. This means that when the water evaporates, the drop can’t shrink in circumference but instead flattens out. That flattening motion pushes water, and anything suspended in it, such as coffee particles, to its edges. By the time the drop fully evaporates, most of the particles have reached the edge and are deposited on the surface, making a dark ring.

    Next: The coffee ring effect and the Line of Marx

    Katherine M. Mastrota, MS, OD, FAAO, Dipl ABO
    Director of Optometry, New York Hotel Trades Council, Hotel Association of New York City, Health Center, Inc.

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