The importance of tears for eye health
In humans, tears form and fall for a variety of different, sometimes inexplicable, reasons – in the aftermath of a painful break-up, after a particularly nasty fall, or even when you are exceedingly happy. Sometimes they even form from non-emotional reasons, such as while cutting up onions while cooking or if you are braving particularly strong windy weather conditions.
In fact, whether you are crying or not, your eyes are actually producing tears all the time. According to the American Academy of Ophthalmology (AAO), your eyes produce as much as 15 to 30 gallons of tears each year. This production of tears is important because tears are essential for clear vision and good eye health, as will be explained later in the article.
How are tears produced?
Lacrimal glands, as seen in the image above, sit above each eye. These are the glands responsible for producing lacrimal fluid, otherwise known as tears. These tears then get distributed across the surface of our eyes when we blink. They get drained through the puncta, tiny holes in the corners of our upper and lower eyelids. From there, tears travel through small canals in the eyelids into the lacrimal sac, and down the nasolacrimal duct. From there, the tears either evaporate or get reabsorbed.
When you are crying, there is an overproduction of tears and this carefully structured lacrimal drainage system gets overwhelmed, causing the tears to spill out of your eyes, run down your cheeks and sometimes even dribble out of your nose.
When you have a blocked tear duct, also known as a nasolacrimal obstruction, the tears being produced constantly in your eyes cannot drain normally, which can cause a watery, irritated or infected eye.
Blocked tear ducts are pretty common in new-born babies – in fact, according to the American Academy of Ophthalmology (AAO), it is estimated that as many as 20 percent of babies are born with a blocked tear duct, and the condition usually gets better without any treatment. In adults, a blocked tear duct may be due to an injury, an infection or a tumour.
Did you know that not all tears are the same?
Yes! In fact, humans actually produce 3 different types of tears – basal tears, reflex tears, and emotional tears. These 3 types of tears are produced in response to different stimuli, and have different functions.
Basal tears are the ones that are constantly being produced all the time to help us lubricate, nourish and protect our cornea (the transparent part of the eye that is in contact with the external surrounding). Basal tears act as a constant shield between our eyes and our surroundings, and help us by keeping dirt and debris away.
Have you ever teared up while cutting onions or while having a smoky barbeque? Or had an eyelash fall into your eye and started tearing up? The tears that form when our eyes are irritated are known as reflex tears. These tears are the ones produced when our eyes need to wash away the harmful irritants it encounters. Reflex tears are produced in much larger quantities than basal tears because they need to flush away the irritant and protect the eyes. Their chemical composition is also slightly different as compared to basal tears – they typically contain more antibodies to help fight bacteria.
Emotional tears are self-explanatory – these are the tears produced in response to strong or intense emotional states like joy, sadness, fear, anger, frustration, among others. Most scientists believe that emotional tears are unique to humans.
What are tears made of?
If you think that tears are just salty water, think again. Every time you blink, a thin layer of tears spread across the surface of your cornea to form a tear film, which are actually pretty complex – in fact, it is made up of three layers, all with different functions. There is the inner mucus (mucin) layer, the watery middle (aqueous) layer and the outer oily (lipid) layer.
The inner mucus layer is the layer that helps tears stick to the surface of the eye. The middle aqueous layer, which is the thickest layer, helps to keep the eye hydrated, repels bacteria and protects the cornea. The outermost lipid layer keeps the surface of the tear smooth for the eye to see through, and to prevent the other layers from evaporating.
What happens if the eye does not produce enough tears?
If you have noticed irritation, burning or blurry vision in your eyes, you may be suffering from dry eye syndrome resulting from a lack of tear production. While most symptoms are not too serious and can be managed, but if left untreated, it may lead to chronic dry eyes, which may lead to more serious vision problems such as a damaged cornea.