What are Tears?
The eyes have both internal and external fluids. Tears are the external fluid. They flow over the eye’s front surface (cornea and sclera) keeping it moist and removing tiny particles of dust and debris. This helps to keep vision clear, removing potential obstacles to the passage of light. Each time we blink, the tears are spread over the eye surface.
Three Tear Ingredients
Tears have three layers, each containing a different ingredient with a different purpose. Each ingredient is produced by a different set of glands.
Sebum – the top layer. Sebum is oily and prevents the tears from evaporating quickly. It is produced by little glands along the eyelids, both upper and lower.
Water – the middle layer. Water provides the main volume of tears and is produced by the lacrimal gland, situated beneath the outer end of the eyebrow. Water helps the tears to spread more easily and helps them remove bacteria from the eye surface.
Mucous – the lowest layer. It is produced by tiny cells in the conjunctiva, the membrane that lines the eyelids and covers the cornea and sclera. Mucous bonds to the water molecules and helps to distribute the tears evenly.
Three Kinds of Tears
There are always tears on the eye surface, even in dry eyes (less tear film in that condition). This ever-present kind is called the basal tears and they contain many elements such as glucose, potassium, and sodium. They also contain some ingredients that fight bacterial infection and are part of the immune system.
Reflex tears are stimulated by a physical cause such as onions, bright light, or spicy food. They provide extra cleansing for the eye surface.
Psychic tears are caused by either physical pain or strong emotions. They may be tears of grief or of joy. They contain a natural painkiller and more of certain hormones. They are accompanied by changes in breathing and some facial reddening and swelling.
The Drainage System for Tears
Tears are continually produced and continually drained away. They flow towards the nose where there are two apertures called puncta lacrimale – one in the lower lid and one in the upper lid. Tears pass through these openings into a duct that takes them to the nose. This is the reason why we have to blow our nose when we cry – the extra psychic tears are accumulating in the nose.
Without this drainage system, tears would often overflow and drip down the cheeks.
There are many causes for dry eyes. Temporary dryness happens often, as after a walk on a windy day, or too long spent at the computer. Those conditions caused the tears to evaporate more quickly than usual, but your tear production is normal. Moisturizing eyedrops from the supermarket can take care of this short-term dryness.
However, there is also a condition known as Dry Eye Syndrome which is chronic because there is dysfunction in tear production. It needs attention from an ophthalmologist and perhaps some prescription eyedrops.
Dry eyes are also a side effect of various other eye disorders, such as ocular rosacea. Part of ocular rosacea is inflammation in the tiny eyelid glands that secrete the sebum in tears. Without sebum, the tears evaporate too quickly, a condition called evaporative dry eye. In many cases this can be managed by using moisturizing eyedrops that contain no preservatives. They come in single-use containers.
Measuring Tear Production
The production of tears by each eye can be measured using various methods. One is Schirmer’s I Test which uses a strip of special paper tucked into each lower eyelid. When they are left in position with your eyes looking forward for five to ten minutes, your eye doctor can read on the paper what level of tears your eyes produced in that time. The score is in millimeters. For example, a score of ten mm over five minutes would be normal but a score of four mm over five minutes indicates dry eyes.
Another method measures how quickly your tears break up. If you stare at something for a while without blinking, your eyes will start feeling uncomfortable and you will blink reflexively. This discomfort is the tears breaking up and blinking moves them, reintegrates them, and allows new tears to move forward over the eyes. If you have chronic dry eyes, your tears break up more quickly and this Break Up Time (BUT) can be measured using fluorescent eyedrops and a blue light.
If you notice your eyes being dry rather often and would like to have them examined by a qualified eye doctor in your area, please contact us today and we will respond promptly.