The lacrimal apparatus is the system responsible for producing, distributing, and draining tears across the surface of your eyes. It keeps your eyes moist, protected from infection, and optically clear. The system works in two phases: the lacrimal gland creates tears and releases them onto the eye, then a network of tiny channels collects used tears and routes them into your nasal cavity. At baseline, your eyes produce roughly 1 to 2 microliters of tear fluid per minute, just enough to maintain a thin, continuous film over the cornea.
Parts of the Lacrimal Apparatus
The system has two functional halves: one that makes tears and one that removes them. On the production side, the lacrimal glands sit behind the upper outer corner of each eye, roughly the size of an almond. These glands secrete the watery portion of your tears, along with key proteins that fight infection.
On the drainage side, four structures work in sequence. The lacrimal puncta are tiny openings on the inner edge of your upper and lower eyelids, near your nose. Every time you blink, these openings act like valves, pulling used tears off the eye surface. From there, tears flow into the canaliculi, short channels that funnel into the lacrimal sac, a small reservoir tucked into the inner corner of each eye. The lacrimal sac prevents old tears from flooding the system all at once, releasing them gradually into the nasolacrimal duct, which empties into your nasal cavity. That connection is why your nose runs when you cry.
In about 94% of people, the upper and lower canaliculi merge into a single channel before entering the lacrimal sac. In a small percentage, they enter separately.
How the Tear Film Protects Your Eyes
Tears are not just saltwater. The tear film that coats your cornea has three distinct layers, each with a specific job.
The innermost layer is made of mucin, a slippery substance that transforms the cornea’s naturally water-repellent surface into one that attracts moisture. Without it, tears would bead up and slide off rather than spreading evenly. This layer also reduces friction during eye movements, cushioning the surface every time you look around or blink.
The middle aqueous layer is the thickest and does the most work. It supplies oxygen to the cornea, smooths out tiny surface irregularities to keep your vision sharp, and carries a concentrated mix of infection-fighting proteins. The cornea has no blood vessels, so it depends on tears and the surrounding atmosphere for oxygen. When your eyes are open, oxygen dissolves through the tear film from the air. When your eyes are closed during sleep, it comes from blood vessels in the inner eyelid. Tears also deliver electrolytes like potassium, calcium, magnesium, and sodium chloride to the corneal surface, though the cornea gets most of its glucose (its primary fuel) from fluid inside the eye rather than from tears.
The outermost lipid layer is an ultra-thin oil film produced by glands along the eyelid margin. Its primary role is to slow evaporation. It also forms a watertight seal when your eyelids close, preventing tears from spilling over onto your cheeks, and it contributes to the optical clarity of your eye surface.
Immune Defense in Tears
Your tear fluid is surprisingly well armed against pathogens. The major antimicrobial proteins produced locally include lysozyme, lactoferrin, tear lipocalin, and secretory immunoglobulin A (sIgA). Together, these form a frontline defense that operates constantly, without any input from your immune system’s slower adaptive responses.
Lactoferrin alone makes up about 25% of the total protein in tears, at concentrations around 1.4 to 2.2 milligrams per milliliter. It works by binding free iron on the eye surface, starving bacteria of a nutrient they need to grow and form colonies. It also blocks viruses from entering the cells of the corneal surface and neutralizes inflammatory molecules like bacterial toxins, flagging them for removal through the constant flushing action of tears. Studies have shown lactoferrin can even inhibit biofilm formation, which is particularly relevant for people who wear contact lenses.
Reflex tears, the kind triggered by irritants like smoke or onion fumes, are produced in larger volumes than baseline tears and contain higher concentrations of antibodies. This is an intentional escalation: when something potentially harmful reaches the eye, the lacrimal gland ramps up both the volume and the antimicrobial strength of the fluid it secretes.
Three Types of Tears
Your lacrimal glands produce tears in three distinct modes. Basal tears flow continuously at a low rate, keeping the cornea lubricated and nourished around the clock. Reflex tears surge in response to physical irritants, wind, bright light, or anything that touches the corneal surface. Emotional tears are triggered by strong feelings and have a slightly different chemical composition, though the lacrimal gland produces all three types.
The cellular machinery behind tear secretion involves specialized cells in the lacrimal gland that perform three tasks simultaneously: they synthesize tear-specific proteins, secrete water, and transport immune molecules (particularly sIgA produced by nearby immune cells) into the gland’s ducts for release onto the eye. Water secretion is driven by the movement of chloride and potassium ions across cell membranes, which pulls water along by osmosis. The resulting fluid has roughly the same overall salt concentration as blood plasma but with notably higher potassium and chloride levels.
What Happens When the System Fails
Problems with the lacrimal apparatus generally fall into two categories: too few tears or poor drainage.
When tear production declines, the result is dry eye. Research on lacrimal gland cells shows a clear age-related mechanism: in younger, healthy tissue, the ion channels that drive water secretion are highly active, maintaining a strong electrical charge across cell membranes (around negative 40 millivolts). In older or diseased tissue, those channels become inactive, the electrical charge drops dramatically, and the cells lose their ability to move chloride ions outward. Without that ion movement, water secretion stalls. This is one reason dry eye becomes increasingly common with age.
When drainage is blocked, tears have nowhere to go and overflow onto the face, a condition called epiphora. A blockage anywhere along the path, from the puncta to the nasolacrimal duct, can cause this. If the lacrimal sac itself becomes infected due to stagnant fluid, the result is dacryocystitis, which causes pain, redness, and swelling at the inner corner of the eye. Newborns sometimes have a membrane covering the lower end of the nasolacrimal duct that hasn’t fully opened, leading to persistent tearing in the first months of life. In most cases, this resolves on its own.