Sunday, October 2, 2011

Let's Talk About Tears!

Before we get to the topic of how to treat Dry Eye let's take a couple of minutes to learn about tears. We have two kinds of tears lubricating the front of our eyes. We have our reflex, or emotional tears. These tears are created by the lacrimal gland that sits up and above our eyes. The lacrimal gland  makes the tears that we cry when we watch a sad movie, or if something gets in our eye.

It's the tears that lubricate our eyes from minute to minute that we are more interested in when we are talking about dry eye. These tears are made by different types of microscopic glands on the surface of our eyes, as well as deep within our eyelids. These tiny glands can be affected by all kinds of medical problems like arthritis, lupus, and the hormonal changes that come with getting older.

Normal tears consist of three different, separate substances. We  have mucin which is created by the goblet cells on the front surface of our eyes. We also have a salt water or aqueous component created by the glands of moll and zeiss. Lastly, we have an oily substance called meibum which is created by the tiny glands that sit just inside our eyelashes on the upper and lower eyelids. These three substances are mixed together, kind of like Italian salad dressing, to form a lubricating layer between our eye and the air.

Shake up a bottle of salad dressing and let it sit for a minute or two. Notice how there is a little bit more oil on the top surface, a thicker middle layer that is a mixture of everything in the salad dressing, and then a layer on the bottom that is really thick. This is a good way to visualize our tears. We have more mucin close to the eye, a mixture or emulsion of mucin and aqueous in the thicker middle, and then a layer which is mostly oil sitting on the surface and preventing evaporation of our tears.

When our tears are healthy we have just the right amount, and we have just the right proportion of the three different components. We start to have problems with dry eye when we either have too few tears, or when the three components do not mix well. Next, we'll talk about the different types of dry. See you soon!

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