5 things you may not know about your tear film

January 18, 2019

Our tears are very important. Tears always form a shield called the "tear film" which covers our eyes, even when we are not crying. Abnormal functioning of tear film could lead to eye problems, such as dry eye disease (DED). Given the significance of tear film, here are five things you should know to get a better understanding of your eye health.

under-hidden-thing01 — Usually, graphic designer’s eyes forcus on screen more than 8 hours everydays

1. Tear film is the frontline defense of our eyes

Tear film is formed and spreads over the eye surface when we blink, covering our cornea. It plays a vital role in keeping the eye surface smooth, clear and moisturized, preventing damage caused by dust, bacteria, or dry air.^1-3

under-hidden-thing02 — Tear film is the frontline defense of our eyes

References

C Stephen Foster. What is the anatomy of tear film relevant to dry eye disease (keratoconjunctivitis sicca)? Medscape. Latest accessed August 25, 2019.
Facts About Dry Eye. The national eye institute. https://nei.nih.gov/health/dryeye/dryeye. Last accessed August 25, 2019.
Dartt, D A, and M D P Willcox. Complexity of the tear film: importance in homeostasis and dysfunction during disease. Experimental eye research vol. 117 (2013): 1-3. doi:10.1016/j.exer.2013.10.008. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4225770/

2. Tear film is not just a saline layer

Have you ever tasted your own tears? Salty right? However, the tear film is not just made of saline fluid. It is a three-layer coating: the outer layer (oil layer), the middle layer (water layer), and the inner layer (mucin/protein layer).^1-3

under-hidden-thing03 — Tear film is not just a saline layer

References

C Stephen Foster. What is the anatomy of tear film relevant to dry eye disease (keratoconjunctivitis sicca)? Medscape. Latest accessed August 25, 2019.
Facts About Dry Eye. The national eye institute. https://nei.nih.gov/health/dryeye/dryeye. Last accessed August 25, 2019.
Dartt, D A, and M D P Willcox. Complexity of the tear film: importance in homeostasis and dysfunction during disease. Experimental eye research vol. 117 (2013): 1-3. doi:10.1016/j.exer.2013.10.008. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4225770/

3. Each layer of tear film has distinctive functions

The outer layer, which is primarily produced by the meibomian gland (oil gland), protects the water layer underneath from evaporating, thus serving as a defense barrier.^1-6

under-hidden-thing04 — Each layer of tear film has distinctive functions

The middle layer, which is produced by the lacrimal gland (tear gland), keeps the eye surface moist, protecting the cornea, and “washing out” pathogens.^1-6
The inner layer is produced by special cells on the eye surface, connecting with the corneal surface and holding the three-layer structure together. It also helps the middle water layer lubricate after every blink.^1-6

References

C Stephen Foster. What is the anatomy of tear film relevant to dry eye disease (keratoconjunctivitis sicca)? Medscape. Latest accessed August 25, 2019.
Facts About Dry Eye. The national eye institute. https://nei.nih.gov/health/dryeye/dryeye. Last accessed August 25, 2019.
Dartt, D A, and M D P Willcox. Complexity of the tear film: importance in homeostasis and dysfunction during disease. Experimental eye research vol. 117 (2013): 1-3. doi:10.1016/j.exer.2013.10.008. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4225770/
Arita R, Fukuoka S, Morishige N. Functional Morphology of the Lipid Layer of the Tear Film. Cornea. 2017 Nov;36 Suppl 1:S60-S66. doi: 10.1097/ICO.0000000000001367. https://www.ncbi.nlm.nih.gov/pubmed/28957980
Jennifer P. Craig, Laura E. Downie. Contact Lenses. (6ed). 2019, pp97-116.
Dilly P.N. (1994) Structure and Function of the Tear Film. In: Sullivan D.A. (eds) Lacrimal Gland, Tear Film, and Dry Eye Syndromes. Advances in Experimental Medicine and Biology, vol 350. Springer, Boston, MA.

4. What happens to tear film in DED?

There are two main types of DED caused by:
Increased evaporation, which could be the result of meibomian gland impairment and outer oil layer dysfunction. Excessive evaporation from the eye surface leads to dryness and even inflammation.^1-6

under-hidden-thing05 — Increased evaporation

Decreased tear production, which could be the result of lacrimal gland impairment and leads to reduced quality of the middle water layer. The tear film becomes unstable and allows dry spots to form on the corneal surface.^1-6

under-hidden-thing06 — Decreased tear production

In the last years, eye doctors in Asia have uncovered a new type of DED, which is called short Tear film Breakup Time (TBUT). If your TBUT is less than 5 seconds in the diagnosis test, you may have one.⁷ In general, one type or another, an unstable tear film is the underlying cause of DED.⁸ Efforts to protect your tear film, therefore, are needed.

References

Suvarna P. Phadatare, et al. A Comprehensive Review on Dry Eye Disease: Diagnosis, Medical Management, Recent Developments, and Future Challenges. Advances in Pharmaceutics. http://dx.doi.org/10.1155/2015/704946
Dry eyes. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/dry-eyes. Last accessed August 25, 2019.
Facts About Dry Eye. The national eye institute. https://nei.nih.gov/health/dryeye/dryeye. Last accessed August 25, 2019.
C Stephen Foster. Dry Eye Disease (Keratoconjunctivitis Sicca). Medscape. Last accessed August 25, 2019.
Li DQ¹, Chen Z, Song XJ, Luo L, Pflugfelder SC. Stimulation of matrix metalloproteinases by hyperosmolarity via a JNK pathway in human corneal epithelial cells. Invest Ophthalmol Vis Sci. 2004 Dec;45(12):4302-11. https://www.ncbi.nlm.nih.gov/pubmed?term=15557436
The definition and classification of dry eye disease: report of the Definition and Classification Subcommittee of the International Dry Eye WorkShop (2007). Ocul Surf. 2007 Apr;5(2):75-92. https://www.ncbi.nlm.nih.gov/pubmed?term=17508116
Tsubota K. Short tear film breakup time-type dry eye. Invest Ophthalmol Vis Sci. 2018;59:DES64–DES70.
Tsubota K, et al. New Perspectives on Dry Eye Definition and Diagnosis: A Consensus Report by the Asia Dry Eye Society. The Ocular Surface. 2017;15(1):65-76.

5. How to protect tear film?

Our tear film can be protected by using these practical tips:^1-2

Reduce screen time and take breaks regularly.
Use eyeglasses/sunglasses to protect the eyes from the sunlight, wind or dry air.
If you have meibomian gland dysfunction, warm pads might help.
Avoid smoking cigarettes and exposure to passive smoking.
Drink enough water and avoid dry, hot air.

References

Dry eyes. Mayo Clinic.https://www.mayoclinic.org/diseases-conditions/dry-eyes. Last accessed August 25, 2019.
Facts About Dry Eye. The national eye institute. https://nei.nih.gov/health/dryeye/dryeye. Last accessed August 25, 2019.

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