Slide show: A look inside your eyes
Illustration of the eyelid
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Your eyes are your windows to the world — but they need to be shielded from the elements to keep you seeing clearly. Upper and lower eyelids protect the front of your eyeballs by blocking foreign objects and bright light. In addition, your eyelids involuntarily open and close (blink) every few seconds when you're awake. During each blink, fluid produced by tear glands passes over the cornea and lubricates the surface of each eye. This helps keep your eyes moist and washes away germs, dust and stray eyelashes.

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