The tear film’s water layer, explained

The water layer, also called the aqueous layer, is the thick middle of the tear film and holds most of its volume. It keeps the surface of the eye wet and smooth and washes away dust. It’s also the part that evaporates: dry, windy, heated or air-conditioned air pulls it off the eye faster, and the thin oil layer above it is what slows that loss.

The middle of three layers

From the eye outward, the tear film runs mucus, then water, then oil. The mucus coat underneath helps the water spread and cling. The oil on top acts like a lid. The water sits between them and does most of the visible work: when you say your eyes are watering, this is the layer you mean.

“Aqueous” simply means watery. You’ll see the word on some eye product cartons and in articles about tears. Quell’s own carton uses it in a before-and-after illustration, and the “before” caption reads: Water (Aqueous) Layer evaporates due to thin, unhealthy oil (Meibum) layer.

What the water layer does

• Keeps the front of the eye moist, which living tissue exposed to air needs.
• Gives light a smooth surface to pass through, which is part of why vision is sharpest right after a blink.
• Rinses away dust, pollen and small bits of debris toward the inner corner, where tears drain.
• Carries a fresh supply across the eye with every complete blink.

Why does the water layer evaporate?

Any water exposed to air evaporates, and the tear film is spread thin across a warm surface, which makes it easy to lose. Between blinks it thins steadily. How fast it goes depends mostly on the air around your face:

• Dry air, from winter heating, desert climates and airplane cabins, takes moisture faster than humid air.
• Moving air, from wind, a ceiling fan, a car vent or a bike ride, carries evaporated moisture away and keeps the process going.
• Heat near the face, from a fireplace, space heater or hair dryer, speeds it up further.
• Air conditioning dries the air while it cools it, so a cold office can be as hard on the eyes as a warm one.

Blinking matters as much as the air. Screens and close reading reduce how often you blink, so the water layer sits exposed longer before a fresh coat arrives. Screens and your tear film covers that side.

Why the oil layer matters for keeping water in

If the water layer were left open to the air, it would disappear quickly. The thin oil layer floating on top slows that down, much as a film of oil on a bowl of broth keeps the broth from cooling and steaming off as fast. When the oil layer runs thin, the water underneath evaporates sooner, and the eye can feel dry even though it’s making tears.

That’s the reasoning behind Quell’s design. Quell is designed to reinforce the tear film’s oil layer to help reduce moisture loss, and the carton’s “after” caption reads: Quell reinforces the tear film’s oil layer to help reduce moisture loss. The tear film’s oil layer goes into that layer in detail, and what is meibum? explains where its oil comes from.

Why do my eyes water if they’re dry?

It sounds backward, but it’s common. When the surface of the eye gets dry or irritated, it can respond with a rush of watery tears. That reflex flood is mostly water, without the balance of the full three-layer film, so it spills over the lid and down the cheek instead of settling into an even coat. A few minutes later the eye can feel dry again.

Cold wind is a classic trigger, which is why eyes stream on a winter walk and then feel scratchy indoors. Watery eyes that come with pain, vision changes, or discharge are a different matter and belong with an eye doctor. Eye symptoms that need a doctor lists them.

Ways to keep more water on the eye

• Add moisture to dry rooms with a clean humidifier, especially the bedroom.
• Point vents and fans away from your face at home, at work and in the car.
• Wear wraparound glasses outdoors on windy days.
• Blink fully on purpose a few times when you look up from a screen.
• Drink water through the day, since the rest of your body dries out in the same air.

What the label says

A lubricating drop adds to the tear film from the outside. Quell’s Uses read: For use as a protectant against further irritation or to relieve dryness of the eye. Its active ingredients are Glycerol (1.0%), Polysorbate 80 (1.0%) and Light Mineral Oil (0.5%), and its directions are Apply 1 drop 3 times per day in each eye. Because the formula contains emu oil, read the warning on the Drug Facts page first: Caution should be used in those with egg or bird allergies — For use in the eyes only.

The label also sets the limit on self-care: Stop use and ask a doctor if you feel eye pain or changes in your vision, if irritation or redness continues, or if the condition worsens or persists for 72 hours. An eye doctor can measure how much water your eyes make and how quickly the film breaks up, which no drop can tell you.