What Causes Chronic Dry Eye?
It is often difficult to find the precise cause of dry eyes. There tends to be multiple factors involved, and, when they occur simultaneously, they can cause further problems.
Dry eyes promote inflammation, which in turn can also cause dry eyes. This leads to a vicious cycle where the symptoms get worse over time.1 It is therefore important to understand what is causing your dry eyes so that you can protect your eyes from damage.
Problems with the Tear Film
Dry eyes primarily occur when not enough tear fluid is produced or when the fluid evaporates too quickly. To better understand how dry eyes develop, you need to know about the three layers of the tear film.
1. The inner mucus layer
The mucus layer lies directly on the cornea and forms the foundation of the tear film. It helps the tear film to spread evenly over the ocular surface and to stay attached.2 Disruptions of this layer can not only lead to dry eyes, but also watery eyes.
2. The middle aqueous layer
The aqueous layer represents the main fluid part of the tear film. When not enough tear fluid is produced, eyes quickly get dry. However, this is rarely the only cause of dry eyes.3
3. The outer lipid layer
The outer lipid layer prevents the tear film from evaporating too quickly. It is produced by the meibomian gland, which is located at the inner lid edge. If this gland becomes inflamed, it can impact the composition of the outer layer and destabilize the tear film. When the lipid layer is too thin, it quickly ruptures, promoting the development of dry eyes. Problems with this layer are the most common cause of dry eyes.4
Multiple risk factors can influence the layers of the tear film and therefore lead to dry eyes:
- Certain medical conditions: Some diseases, such as diabetes, autoimmune diseases, or hypothyroidism, can cause dry eyes to develop.5,6,7
- Allergies: An allergy is an overreaction of the immune system to technically harmless substances. This is associated with inflammatory responses that can lead to dry eyes.8
- Medications: Some medications, such as antidepressants, cholesterol-lowering medications, beta-blockers, neuroleptics, and antihistamines, can cause dry eyes as a side effect.9
- Age: Tear production decreases with age.10 Older people also tend to take medications that can cause dry eyes.
- Hormones: Women are more likely to experience dry eyes than men, and this is usually because of hormonal changes. Women primarily experience dry eyes during pregnancy or menopause.11
- Vitamin A deficiency: Vitamin A is vital for eye health and function. A lack of this vitamin can consequently cause dry eyes.12
- Incomplete eyelid closure: The eyelids are necessary to moisturize the eyes. When the eyelids don’t close completely (for example after surgical intervention), dry eyes can easily develop.13
- Non-corrected, poor eyesight: People who don’t see well tend to stare and blink less frequently.14 This leads to an insufficient moistening of the eye.
- Refractive eye surgery: Dry eyes are one of the most common symptoms after refractive eye surgery. This is usually temporary but can be permanent.15
- Contact lenses: Contact lenses can damage the outer lipid layer of the tear film, which protects against evaporation.16 People who wear contact lenses daily for many hours are at high risk of developing dry eyes.
As mentioned, dry eyes are usually caused by multiple factors. Environmental conditions can cause dry eyes to develop by irritating the eyes or by promoting the evaporation of the tear fluid.17
- Dry air, due to either heating or air-conditioning, causes the tear fluid to evaporate too quickly.
- Fumes from air pollution irritate not only the airways but also the eyes and can thereby indirectly trigger dry eyes.
- Direct sunlight, orUV-light, can damage the cornea, which can cause dry eyes.18
- Cosmetics, such as eye make-up, foundation or face cream, can damage the tear film if they run into the eye.
- Working in front of a screen for many hours is also a risk factor. The ocular surface gets moisturized with each eyelid movement. Your blinking rate is highly individual, but the average is around 17 eyelid movements per minute.19 This rate can go down to a few movements per minute when working at a computer.20
The Causes of Dry Eyes Are Multifaceted
Dry eyes are often caused by a high evaporation rate, which is caused by an instability of the tear film’s outer lipid layer. Several factors can influence the composition of this layer. In many cases, a combination of environmental and physical factors leads to dry eyes. Inflammatory responses play a vital role because they are both caused by dry eyes and can also aggravate dry eyes.
As there are many different causes of dry eye, there are also different promising treatment options, like artificial tears. When working at the computer, using a software like BlinkGuard to increase your blink rate can cause strong improvements as well.
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2. Zhang X, M VJ, Qu Y, et al. Dry Eye Management: Targeting the Ocular Surface Microenvironment. International Journal of Molecular Sciences. 2017;18(7):1398. doi:10.3390/ijms18071398
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