Dry Eye Syndrome: Causes
Everyone will experience dry eyes at some point, even if it is just a temporary situation. The burning, redness, grittiness, blurry vision, and even watering can usually be traced back to a source of dryness. Dry eye syndrome, or dry eye disease, can be caused by an overwhelming number of reasons. This blog is the first of our Dry Eye Series, which will explain the most common causes of this popular condition.
Composition of Tears
The tear film is composed of three major layers: mucin, aqueous, and lipid. If one of the layers is not doing its job, dryness can occur. There are different types of dry eye based on which layer is functioning poorly.
1. Mucin (mucus-like): The mucin layer is produced by the goblet cells of the conjunctiva (the clear, thin membrane on top of the white part of the eye). Its function is to resurface or fill in any irregularities of the cornea.
2. Aqueous (watery): The lacrimal (tear) gland produces the aqueous layer. It provides oxygen, nutrients, and antimicrobials to the tears.
3. Lipid (oily): The lipid layer comes from the meibomian glands that line the margin of the eyelid. Its oily consistency helps prevent tears from evaporating into open air and keeps the eyes feeling lubricated.
Common Causes of Dry Eye Syndrome
Decreased Tear Production
When the lacrimal gland does not make enough tears, the type of dry eye syndrome is classified as “aqueous deficiency dry eye.” There are many reasons why decreased tear production may occur. The most common, and simplest, cause is normal aging. Thyroid conditions and autoimmune disorders, such as rheumatoid arthritis, Sjogren’s syndrome, and lupus, can cause inflammation of the lacrimal gland. The inflammation can decrease the lacrimal gland’s ability to adequately produce tears. Tumors and radiation damage can also hinder tear production. Some medications (antihistamines, antidepressants, anti-hypertensives, etc.) can lead to dry eye syndrome as well.
Meibomian Gland Dysfunction
If the meibomian, or oil, glands lining the upper and lower eyelids become blocked or don’t produce enough oil, then “evaporative dry eye” may occur. The top layer of tears is composed of this oil, which acts as a barrier to help the tears from instantly evaporating when the eyes are open. Meibomian gland dysfunction is common in people with poor eyelid hygiene, blepharitis, and skin conditions like rosacea.
LASIK and cataract surgeries can lead to dry eye syndrome from the disturbance to the cornea. Sometimes the medicated drops, to minimize the risk of infection and swelling, can cause irritation to the front of the eye. The benefits of using the drops outweigh the risks, so it is very important to continue using all prescribed drops after surgery, unless told otherwise by your eye doctor. The dryness is usually temporary, however, some individuals may experience symptoms even long after the healing process has finished.
Computer Vision Syndrome
Digital eye strain, or computer vision syndrome, has been a popular cause of dry eye syndrome. When using a computer or tablet, the blink rate greatly decreases. If fresh tears are not spread over the cornea at an appropriate pace, the tears will evaporate and dryness ensues. We tend to focus so much on the screen that we forget to blink!
Evaporative dry eye can also be caused by being in certain environments, even just temporarily. Windy or dry air speeds up the evaporation of tears. Ceiling fans or air vents blowing on the face can expedite the process too. If the eyelids don’t fully close during a blink, there will be an area of the eye that doesn’t receive the necessary amount of lubrication. This can be due to poor elasticity of the eyelids from aging. Thyroid conditions and the aftermath of a stroke can also inhibit one’s ability to fully close the eyes. This can be a serious issue that leads to permanent scarring and vision loss in severe cases.
Stay tuned for our next blog in the Dry Eye Series to learn more about this ever-growing phenomenon!