A Tear Film Does More Than Keep the Eye Wet
The eye’s clear front surface, the cornea, has no blood vessels to deliver oxygen directly. It depends partly on the tear film—a constantly renewed coating that keeps the surface smooth and helps wash away tiny particles. The film also helps light pass cleanly into the eye: when it breaks up, vision can briefly blur until the next blink spreads it again.
Tears are a mixture, not simply water. Their watery portion carries dissolved salts and protective substances; oily material from glands along the eyelids slows evaporation. Mucus-like components help the fluid cling to the eye rather than bead up and slide off. A problem with any part of this balance can leave the eyes dry or irritated, even when they seem watery.
Where the Fluid Goes
At the inner edge of each eyelid are tiny openings called puncta. With each blink, the lids help move fluid toward these openings. It then passes through narrow channels into the nose. That route explains why tears can make a runny nose during crying: excess fluid drains into the nasal cavity, while some also evaporates from the eye.
The system handles ordinary lubrication quietly, but irritation can change the output. Smoke, a stray eyelash, or a dry surface can trigger reflex tearing—an extra response meant to dilute or flush away the irritant. The same drainage pathway carries that overflow, turning a subtle maintenance system into something suddenly noticeable.
