How come when you squint at a bright light, light beams seem to appear on the top and bottom of the source?
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Normally, your tear film forms a uniform layer over the front surface of your eye.
When you squint, your eyelids act as a wiper blade to sweep up a “wave” of tears from the top and bottom eyelids. This tear wave is curved vertically and acts as an cylindrical lens to spread out light into your eye in the vertical direction.
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