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How does the environment affect dry eye disease?

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As we move through life, our environments are often changing. Whether it be sitting in a snowy country or moving to a more urbanised country, we are constantly facing new circumstances. But oftentimes these changes have become second nature to us, and the repercussions that our environment can have on our health may not be at the forefront of our minds. One of the most common eye problems that may be caused or made worse by your environment is dry eye disease. Read on to find out how the environment can affect dry eye.

 

What is dry eye disease?

According to the Tear Film and Ocular Surface Society (TFOS) [1], dry eye disease (DED) is a multifactorial disease related to changes in the quality and quantity of tears on the surface of the eyes that causes symptoms of discomfort, visual disturbance, and tear film instability with potential damage and inflammation to the surface of the eye. While DED can be caused by multiple different situations and factors, the underlying reason for the symptoms is that the cornea isn’t being properly and adequately lubricated by the tear film that the eye is producing. The cornea is the transparent part of the eye that covers the front of your eye. Tears are produced by a gland behind your eye called the lacrimal gland. There are 3 layers that make up tears; the innermost mucous layer, the watery middle layer, and the oily outermost layer. These 3 layers combined are known as tear film.

There are several types of DED, the two most common being aqueous deficient dry eye (ADDE) and evaporative dry eye (EDE). ADDE is a failure in the lacrimal gland’s ability to secrete tears, or the conjunctiva failing to lubricate the cornea with the watery middle layer of the tear film. The conjunctiva is a transparent, thin membrane that covers the sclera (“white” of the eye) and is covered by the cornea. Because ADDE is normally caused by an internal problem within the eye, it is less likely to be connected to your environment. However, your environment can make you more susceptible to EDE.

EDE is the excessive loss of water from the surface of the eye, while the lacrimal gland’s secretion function is still intact. This means that an external factor or ocular habit, like blinking too little, is the likely cause of EDE.

Evaporative dry eye (EDE) and your environment:

There are two subcategories of EDE: intrinsic, and extrinsic. Intrinsic EDE is when the dry eye is caused by a more mechanical problem, such as a low blink rate or poor eyelid functionality. Extrinsic EDE is caused by other factors, such as a vitamin A deficiency to improper contact lens wear. However, weather conditions and season changes can also impact dry eye symptoms and can exacerbate symptoms of oxidative stress.

Oxidative stress is when there is a disturbance in the balance between single oxygen particles (free radicals) and antioxidant defences.  Free radicals cause damage to other cells in the body by trying to pair with one of the oxygen atoms from the surrounding healthy cells. Antioxidants are molecules that defend against the effects of free radicals. When there is an imbalance between free radicals and antioxidants, the free radicals cause damage to the body’s cells which can result in deterioration of those cells. There are specific environmental factors that can increase oxidative stress including: air pollutants, ultraviolet radiation (from the sun) and smoking [2].

In a study by Gysbert van Setten et al. [3], the researchers investigated the effects of seasons and weather on patients with dry eye and the impact on their symptoms. They interviewed 738 patients suffering from dry eye disease and asked them about the impacts of the four seasons, and a variety of weather conditions, and whether they felt that their symptoms were any different depending on these conditions. Their results showed that almost half (47%) of the respondents found that seasonal conditions had a high impact on their dry eye symptoms, with summer and winter being the two seasons most commonly associated with dry eye complaints (for 51% and 43% of participants, respectively). Wind was also reported to be the most aggravating condition to the participants’ dry eye symptoms with 71% noting this change, and sunshine close behind at 60%.

While wind is not known to have a direct link to DED, based on these results the researchers have hypothesised that the symptoms are more exaggerated under these conditions because of higher evaporation rates. Most people with DED and particularly EDE suffer from an accelerated evaporation rate [4]. A second-hand effect of wind is increased evaporation of the tear film and more rapid tear fluid flow. This correlation in symptoms, leads to increased dry eye complaints [5].

If you experience any of these signs and symptoms mentioned in the article, schedule an appointment with an eye health professional to get your eyes checked. It is also important to note that the development of eye conditions may even start before symptoms appear, which makes going for regular and timely eye checks that much more essential.

 

References:

[1] Michael A Lemp, M.D. and Gary N Foulks, M.D., F.A.C.S. The Definition and Classification of Dry Eye Disease: Guidelines from the 2007 International Dry Eye Workshop. Tear Film and Ocular Surface Society. 2007.

[2] Sophia Seen, Louis Tong. Dry Eye Disease and Oxidative Stress. Acta Ophthalmologica, volume 96, issue 4, page e412-e420. 2017.

[3] Gysbert van Setten, Marc Labetoulle, Christophe Baudoin, Maurizio Rolando. Evidence of Seasonality and Effects of Psychometry in Dry Eye Disease. Acta Ophthalmologica, volume 94, issue 5, page 499-506. 2016.

[4] M Rolando and M F Refojo. Tear Evaporimeter for Measuring Water Evaporation Rate from the Tear Fear Under Controlled Conditions in Humans. Exp. Eye Res. 36: 25-33. 1983.

[5] C C Peng, C Cerretani, R J Braun and C J Radke. Evaporation-Driven Instability of the Precorneal Tear Film. Adv Colloid Interface Sci 206: 250-264. 2014. 

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