Tears are a universal human experience. While commonly understood as a watery discharge from the eyes, tears are complex. Exploring them from a scientific and medical perspective reveals their intricate composition and various functions.
The Official Name for Tears
The medical term for the fluid commonly known as tears is “lacrimal fluid.” The process of producing and secreting this fluid, particularly when in excess, is called “lacrimation.”
Lacrimal fluid is a watery substance produced by the lacrimal glands, designed to lubricate the eye and combat bacteria. The term “lacrimal” itself originates from the Latin word “lacrima,” meaning tear.
The Science Behind Tear Production
Lacrimal fluid is continuously produced by specialized structures within and around the eyes. The primary lacrimal glands, located above the outer corner of each eye, generate most tears. Smaller, accessory lacrimal glands also contribute to tear production, particularly for basal tear secretion.
Once produced, tears spread across the eye’s surface with each blink, then drain through a sophisticated system. This pathway begins with tiny openings called puncta on the inner corners of the eyelids, leading into small tubes called canaliculi. Tears then collect in the lacrimal sac and pass through the nasolacrimal duct, emptying into the nasal cavity. This connection explains why a runny nose often accompanies crying.
Tears are not merely water; they form a complex, three-layered film known as the tear film. The outermost layer is the lipid (oily) layer, produced by the Meibomian glands along the eyelid margins. This layer helps prevent the rapid evaporation of tears, ensuring the eye remains moist.
Beneath the lipid layer is the aqueous (watery) layer, the thickest component. Secreted primarily by the lacrimal glands, this layer provides moisture, oxygen, and nutrients to the cornea. It also contains electrolytes like sodium and potassium, and proteins that offer antibacterial protection.
The innermost layer, the mucin (mucous) layer, is produced by goblet cells in the conjunctiva, the membrane lining the inside of the eyelids and covering the white part of the eye. This layer helps tears spread evenly across the eye’s surface, creating a smooth optical surface for clear vision.
Why We Have Different Types of Tears
The human body produces different types of tears, each serving a distinct purpose in maintaining eye health and responding to stimuli. These include basal, reflex, and emotional tears.
Basal tears are produced constantly in small amounts to keep the eye lubricated, nourished, and protected from dust and debris. They maintain the health and integrity of the cornea, the clear front surface of the eye.
Reflex tears are produced in larger quantities as a protective response to irritants. When foreign particles, smoke, or onion fumes contact the eye, reflex tears flush them out. These tears can also contain a higher concentration of antibodies.
Emotional tears are shed in response to strong feelings such as joy, sadness, or pain. Research suggests they may have a slightly different chemical composition than other types, potentially containing higher levels of stress hormones and proteins. The act of crying emotionally may play a role in emotional release and stress reduction.
When Tears Don’t Work as They Should
When the tear production or drainage system malfunctions, eye conditions can arise. Dry eye syndrome occurs when eyes do not produce enough tears or when tears are of poor quality. This can lead to discomfort, burning, and a gritty sensation.
Epiphora is the medical term for excessive tearing or watery eyes. It can result from an overproduction of tears or a problem with the tear drainage system. Environmental irritants or allergies, for instance, can cause increased tear production.
Blocked tear ducts are a frequent cause of epiphora, where drainage pathways become obstructed. This blockage prevents tears from draining into the nasal cavity, causing them to accumulate and spill over the eyelids. A blocked tear duct can also increase the risk of eye infections due to stagnant tears.