The cornea is the thin, clear outer layer of your eyeball—the windshield of your eye. And when your cornea is swollen, a too-strong rub could tear it, McMonnies says. There are two distinct times when a lack of oxygen renders your cornea swollen, McMonnies adds: When you first wake up in the morning, and when you remove your contact lenses at night. Try not to rub at those times, he stresses. A tear is not only excruciatingly painful—like a pin stab in your eye—but it could render you blind.
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