Why are your eyes dry?

-All about the glands

Many people come to the eye clinic complaining of dry eye—burning, sandy, foreign body sensation, tearing, and redness. Many don’t complain, but their eyes look dry under slit lamp—a magnifying device eye doctors use to examine eye health. So why are my eyes dry? You ask.

You probably know that our tears are made and secreted by a tear gland, or lacrimal gland. We have a main lacrimal gland that is above the eye, and several smaller glands scattered throughout conjunctiva, the clear membrane that covers the white part of the eye as well lining the inside of the eye lids. These glands produce the water part of the tears, and when you cry, a large amount is produced. This is the water or aqueous layer of the tear film. Do you know that there is another layer covering this water layer and that layer is actually made of fat? It is much thinner than the water layer, but it is there to prevent the evaporation of the water layer, in other words, seal the moisture. Without this fat layer, tear will quickly evaporate, leaving the surface of the eye dry. It turns out, that majority, or 70% of all dry eye cases are caused by deficiency or problem with the fat layer.

meibomian-glands-660x573

So what makes the fat layer of the tear film? Large sebaceous gland inside the upper and lower eye lids make them. These are called Meibomian glands. These are just like sebaceous glands in the skin, making oil and secreting it to lubricate the skin, or in the case of Meibomian glands, seal the moisture on the surface of the eye. The oil is released each time you blink, onto the lid margin via small ducts, then mixes with the tear and forms the outer layer.

You may have heard your eye doctor say to perform warm compress and lid scrub to your eyelids to alleviate dry eye. This is actually the standard first line treatment for mild dry eye. Ever wonder why? The warm compress warms up the oil and makes it more fluid like just like when you heat up butter to make it liquid, then the scrubbing action exfoliates debri and other materials that block the meibomian gland duct opening on the lid margin, allowing the lipid to flow out of the duct to the eye surface. Many people who suffer from dry eye have their Meibomian gland duct blocked, not unlike clogged sebaceous gland of the skin which when inflamed gives you acne. Warm compress and lid scrub can effectively open up those glands again so you get lipid in the tear to make tear film longer-lasting. Some doctors will recommend using baby shampoo, some recommend using mineral oil when doing the scrubbing. As long as you consistently do it at least twice a day for 2-4 weeks, for just 5 min each time, you will experience the difference, even if you just use clean warm water and a clean wash cloth without any additional product. After dry eye is resolved, you want to maintain this routine for once a day every day to keep your Meibomian glands open and happy and keep dry eye at bay.

So why do the Meibomian gland ducts get clogged up? It is not known why, but as we get older, there is more keratinization going on in that ductal area, making the duct opening narrower, which causes some accumulation of the fat at the opening, sometimes ‘capping’ the duct opening. Once that happens, oil can no longer come out and you experience dry eye. Long-term clogging of ducts lead to increased oil accumulation and increased pressure inside the gland, which may cause gland atrophy, which means the gland gets smaller and under functions. If this goes on for long enough, the entire gland can drop out, so no more oil can be produced.

I have an analogy that breast-feeding mums may appreciate. When your milk ducts are clogged, you get engorgement. After painfully massaging, squeezing, warm or cold compressing, you notice your milk production decreases, which you have to pump a whole lot to restore the production, or in some situations, you never get that amount of mild back. Sometimes in addition to engorgement, you can also get mastitis, painful inflammation with fever that is actually quite dangerous. For Meibomian glands, clogged ducts sometimes can also lead to a bump on the lid, or chalazion. The treatment again is warm compress, lid scrub for many days, sometimes weeks to months, to open the duct, allowing fat to come out; or if it’s very severe, a small surgery is needed to drain the fat out. For some people, chalazion can recur, and it is not a pleasant thing to have.

Oh I forgot to mention that all this problem with the Meibomian gland which results in dry eye is called Meibomian gland dysfunction, or MGD for short. When MGD is caused by clogging of duct, it is termed obstructive MGD. In some cases though, the duct is open, but the gland just fails to produce enough amount or quality of fat to lubricate the eye. Why so? It is not clear, but scientists hypothesize that when we get older, our hormones, specifically sex hormones, growth hormone, and IGF-1 decline, and since these hormones drive the sebaceous glands to produce oil, our skin gets dryer, as is our tear less ‘oily’ and more evaporative. It is noteworthy that some people’s Meibomian gland produces too much oil, or oil that is too viscous, which is prone to clogging, leading to MGD and dry eye. Therefore, a healthy Meibomian gland that produces proper amount and good quality oil is key to eye surface health.

What about the water part of the tear? Isn’t the bulk of the tear film actually water? It turns out that dry eye solely due to water or aqueous deficiency is much less common than MGD or evaporative dry eye. One example is Sojgren’s syndrome, an autoimmune condition where the body’s immune system attacks the lacrimal gland (as well as salivary gland), leading to dry eye and dry mouth. But this is a rare disease.

What about artificial tears? You may ask. They certainly are a good substitute if your own tears are drying out too quickly. And I will talk about them in a separate article. Here is the thing though, while they relieve the symptoms for some, for others, they may need to be put in too many times a day to be helpful. This is because whatever is put in the eye, drains out pretty fast into the nose. You know this after you cry, your tears come out of your nose so that your eyes are not flooded. There are all sorts of formulas and some of them stay on the eye for longer than others. But if your own gland is healthy, it will be constantly pumping out good oil to make the tear long-lasting.

So do not forget to blink. We stare at the computer or our phones for too long, and forget to blink. Remember that blinking is necessary to bring out the oil and distribute the tear film evenly across the surface of the eye. So blinking frequently helps the dry eye.

 

Here is how to do warm compress and lid scrub:

  1. soak a clean wash cloth with clean and warm water, semi-dry out the cloth like when you wash your face
  2. close eyes and put the cloth on eyelids till it’s no longer warm
  3. now scrub eye lids along the entire lids while eyes are closed for a few seconds
  4. repeat above and do this for 5 min.
  5. do this twice to four times a day.

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