Tears and eye health

Tears are complex. They can happen because of an injury, emotional distress or even while chopping onions. Babies cry when they need something. And your eyes may water when you’re exposed to allergens and other irritants.

No matter the reason for your tears, they’re a vital part of eye health. They keep the eyes moisturized, flush out dirt and particles, and act as a release for both emotions and physical pain.

So what’s behind the structure of tears? What are they made of, and how does the body produce them to begin with? Here’s a deep dive into the composition of human tears.

Natural tears are made of enzymes, electrolytes, metabolites and lipids. The material is similar to saliva. 

Tears have three layers. When grouped together, these layers are also known as tear film: 

• The oily outer layer keeps the eye’s surface smooth and prevents the other layers from drying out.
• The watery middle layer protects the cornea (the clear surface of the eye), keeps bacteria from getting into the eye, and helps keep the eye hydrated. It’s the thickest layer of the three.
• The inner layer, made of mucus, keeps tear film attached to the surface of the eye.

Image Source: National Institutes of Health (NIH)

Tears spread across the cornea every time you blink in a thin film (tear film). They form in the lacrimal glands above the eyes and flow into the tear ducts (tiny tubes in the inner corners of the eyes). 

Then they make their way down through the nose. After this exciting journey, tears are either reabsorbed or they evaporate. 

The harder you cry, the more you can overload the tear drainage system. When this happens, tears flow more rapidly out of your eyes and nose.

READ MORE: Punctum of the eye

Humans form several different kinds of tears. Whether you knew it or not, you’ve produced all three types:

• Emotional tears — The tears you cry in response to an emotional event. This could involve any emotion, whether it be happiness, grief, fear, stress, or even physical pain. According to scientists, emotional tears may include hormones that are not present in the other two kinds of tears.
• Basal tears — These are constantly produced in your eyes as a way of protecting them from dirt and debris. They also lubricate the cornea.
• Reflex tears — The tears that form when you are exposed to something that irritates your eyes. This can include environmental irritants such as smoke or dust. They also form when you chop onions or get something stuck in your eye. These tears have more antibodies than other tears in order to defend against bacteria. 

What are crocodile tears?

Crying “crocodile tears” is a phrase used to describe when someone pretends to be upset about something when they aren’t, especially if they have ulterior motives. You may also hear someone say “alligator tears” when describing the concept. 

The origin of the phrase comes from a myth that crocodiles cry while eating their prey. 

While “crocodile tears” is used as a saying for insincere grief, one researcher from the University of Florida observed alligators and caimans, and found that they actually do tear up while they chow down. 

He believes this is due to the amount of air pushed into their sinuses as they “hiss and huff” during feedings. It likely has nothing to do with feeling (or faking) any emotion, including sadness or remorse.

What are tear troughs? Are they caused by crying?

Tear troughs are small, concave deformities of orbital fat located under the eyes. They’re usually 2 to 3 centimeters in size and have the appearance of a large dark circle. People who have tear troughs often look very tired.

Tear troughs are caused by aging and are sometimes inherited. Despite the name, they are not caused by crying. 

Surgical and nonsurgical procedures are available to remove tear troughs for those who wish to do so.

A person with normal tear production produces between 15 and 30 gallons of tears every year. But the ability to produce tears can be impacted by several things, including:

• Hormones, especially during hormonal changes such as pregnancy and menopause
• Dry eyes and dry eye syndrome
• Taking certain medications
• Wearing contact lenses
• Blepharitis
• Aging, as the body makes fewer basal tears over time

If you’ve noticed a change in your tears, or if you experience chronic or severe dry eye, contact your eye doctor for an evaluation.

SEE RELATED: Watery eyes: Common causes and treatments 

Like real tears, artificial tears play an important role in providing the eyes with moisture. But instead of the natural substance found in real tears, these lubricating eye drops are made of mild ingredients that mimic tears’ natural structure.

There are several ingredients found in artificial tears, each designed with a different purpose. This includes two main active ingredients known as demulcents and emollients, along with preservatives* and other additives. Together, these ingredients work together to lubricate the eyes, reduce irritation and more.

*Preservatives can be irritating to some, so they are not found in some artificial tear formulas.

Why are these ingredients important?

The purpose of each ingredient is as follows: 

• Demulcents — water-soluble polymers that help protect and moisturize the eye’s mucous membranes. Common demulcents include hydroxymethylcellulose, carboxymethylcellulose and propylene glycol. Others include glycerin, polyethylene glycol and propylene glycol.
• Emollients — oils and fats that increase the thickness of the lipid layer, decrease evaporation and keep the tear film stabilized. Some common emollients include castor oil, flaxseed oil and mineral oil.
• Preservatives — these are sometimes added to the eyedrop’s formula to prevent bacteria from growing inside the bottle after it’s opened. OcuPure, benzalkonium chloride (BAK), polyquaternium (Polyquad) and polixetonium are all types of preservatives that may be used. Sodium chlorite may also be used as a more mild preservative.
• Additives — additional ingredients designed to balance the pH of the eyedrop so that it closely matches the pH of natural tear film (and to reduce irritation while using the product). This can include inactive ingredients such as electrolytes, osmoprotectants, emulsifiers and buffers.

Not every type of eye drop includes the same ingredients. Many eye drop formulas are also preservative-free, because preservatives can cause irritation and other unwanted effects.

What are artificial tears used for?

Artificial tears are used to treat the the following eye symptoms:

• Short-term dry eyes caused by digital eye strain, allergies or harsh weather conditions
• Redness caused by tiredness, allergies or other irritants
• Soreness or swelling caused by crying or allergies
• Irritation associated with infections such as viral conjunctivitis
• Moisture and relief for some types of keratopathy (corneal disease)

There are many other types of eye drops on the market that have different uses. Aside from artificial tears, you may come across drops such as decongestant eye drops, antihistamine eye drops and prescription eye drops for serious conditions.

Talk to your doctor before using any new eye products that you are unsure about. Your doctor may recommend or prescribe a specific product based on your condition and the sensitivity of your eyes.

SEE RELATED: Tear Trough Filler

They may not be related to emotions, but like humans, dogs also produce tears. Many dogs experience some eye discharge in the corners of their eyes, which can be caused by allergies or dry eyes. 

Eye discharge in dogs is often not a major reason for concern, but if you have doubts, contact your veterinarian.

What are tear stains on dogs? 

Dogs can get reddish-brown “stains” under their eyes from their eye discharge. The staining is more obvious in dogs with light-colored fur. It’s not usually a medical concern, and can be treated simply by keeping the eyes clean with a damp washcloth and trimming excess fur in the area.

Tears in humans and animals are an important component of eye health. Tear production may be disrupted by various causes, but it can generally be treated by addressing the underlying cause (sometimes with the aid of artificial tears). 

Talk to an eye doctor if you have questions about your vision, whether it’s related to tears or not. And don’t forget: It’s always OK to cry.

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