Tear glands, or lacrimal glands, are the small structures responsible for producing the fluid that becomes tears. This fluid is fundamental for maintaining the health and proper function of the eyes. It provides a protective film that shields the eye’s surface, keeping it clean, lubricated, and nourished. Without the constant production from these glands, eyes would be vulnerable to damage and impaired vision.
Anatomy of the Lacrimal System
The system responsible for tear production and drainage is a complex network of glands and ducts. The main lacrimal glands, each about the size of an almond, are situated in the upper, outer portion of each eye socket, just behind the orbital rim. These primary glands are responsible for the bulk of tear production, particularly in response to irritants or emotion. They are divided into two sections: a larger orbital lobe and a smaller palpebral lobe.
Supporting the main glands are smaller, accessory lacrimal glands located within the conjunctiva, the thin membrane lining the inside of the eyelids. Once tears are produced, the act of blinking spreads the fluid evenly across the eye’s surface. The tears then flow toward the inner corner of the eye, where they drain into tiny openings called puncta.
From the puncta, tears travel through small channels known as canaliculi into the lacrimal sac. This sac acts as a reservoir before emptying into the nasolacrimal duct. This duct is a channel that passes through the bone of the nose and drains the tears into the nasal cavity, which is why crying often leads to a runny nose.
The Purpose and Types of Tears
Tears are a complex fluid with a layered structure designed to protect and sustain the eye. The composition and purpose of tears vary depending on their type. There are three distinct categories: basal, reflex, and emotional tears. Each type plays a specific role in ocular health.
Basal tears are produced continuously to lubricate and protect the eyes. These tears form a constant shield that keeps the cornea—the eye’s transparent outer layer—moist, nourished, and clear of dust and debris. They are composed of three layers: an oily outer layer from the meibomian glands to prevent evaporation, a watery middle layer from the lacrimal glands for hydration, and an inner mucus layer to help the tear film adhere to the eye.
Reflex tears are produced in response to sudden irritants, such as smoke, onion vapors, or a foreign object in the eye. Released in much larger quantities than basal tears, their primary function is to flush out harmful substances. They may also contain a higher concentration of antibodies to help fight invading bacteria.
Emotional tears are generated in response to strong feelings like sadness, joy, or stress. Research suggests that the chemical makeup of emotional tears is different from the other types. They contain higher levels of protein-based hormones, including prolactin and adrenocorticotropic hormone, as well as a natural painkiller called Leu-enkephalin. This composition has led to theories that emotional crying may be a mechanism for removing stress-related chemicals from the body.
Common Tear Gland Disorders
Disruptions to the lacrimal system can lead to discomfort and vision problems. Several common disorders can affect tear production and drainage, stemming from issues with either the glands or the ducts. These conditions can range from mild irritation to more significant inflammation requiring medical attention.
One of the most prevalent issues is Dry Eye Syndrome, which occurs when the glands fail to produce a sufficient quantity or quality of tears. This can result from aging, certain medications, or environmental factors. Without an adequate tear film, the eyes can feel gritty, irritated, and become more susceptible to infection.
Excessive tearing, or epiphora, occurs when the tear drainage system is compromised. This is often caused by a blockage in the nasolacrimal duct that prevents proper drainage, not an overproduction of tears. As a result, tears overflow from the eyes.
Dacryoadenitis is inflammation of the lacrimal gland. This condition can be acute or chronic and is often caused by a viral or bacterial infection, such as the Epstein-Barr virus. Autoimmune disorders like Sjögren’s syndrome can also cause chronic inflammation. Symptoms include swelling and pain in the upper, outer corner of the eyelid.