In April of 2016, I received a note from Charles and Brenda Beard who asked if I had ever studied the subject of tears? I put that in my list of topics to investigate thinking that types of tears could not be very complicated. There should be only one type of tears that came with different kinds of situations. Upon researching tears, I have learned that there are three types of tears, and they are different in function and different in composition.
BASAL TEARS keep the cornea of the eye continually wet and nourished. They also lubricate the eye and keep it free of dust. Tears of this type contain water, mucin, lipids, lysozyme, lactoferrin, lipocalin, lacritin. immunoglobulins, glucose, urea, sodium, and potassium. The substances such as lysozyme fight against bacterial infection by dissolving a layer in the outer coating of certain types of bacteria. This action is part of the body’s complex immune system.
Basal tears also contain antioxidants including ascorbate, urate, cysteine, glutathione, and tyrosine. For those of us that aren’t biochemists, this simply means there is a complex, designed system in the tear production of our eyes. This system keeps this vulnerable, exposed surface from being destroyed by agents in the world around us that would attack such a sensitive area.
Typically a person will secrete .03-.04 ounces (.75-1.1 grams) of this body fluid per day. If you have had a family member or even a pet that could not produce tears, you know that very quickly the eye becomes unusable. Basal tears are a carefully compounded chemical substance essential to our vision.
REFLEX TEARS attempt to wash away anything that irritates the eyes. When foreign particles or irritants contact the eye or nasal area, TRP (amino acid) channels in the ophthalmic nerve act to produce these tears. Most of us have produced tears when working with certain substances such as when cutting onions. Tear gas, pepper spray, or some fragrances cause this same reaction. Yawning, coughing, or vomiting can trigger these tears. Bright lights shining in your eyes or hot, peppery substances in your mouth also trigger reflex tears. The fluid, which is water laced with amino acids, help to wash away the irritant.
Those are two types of tears that are very important. There is also a third type which we will talk about tomorrow.
–John N. Clayton © 2018
Data from the American Academy of Ophthalmology.