What causes the vertical shafts of light when you squint?

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Offline thingymijig

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What causes the vertical (relative you your head) shafts of light, which appear when you squint at a bright light source? They move with you as you twist your head, and seem to be more pronounced when you eyes are watering, maybe something to do with that?

Cheers,
Joe

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Offline Soul Surfer

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What causes the vertical shafts of light when you squint?
« Reply #1 on: 10/05/2011 00:27:55 »
Presumably you mean look at the light through almost shut eyes.  There are two effects that may play a part in producing this effect  Firstly diffraction and secondly the meniscus between the fluid on our eyes and the eyelids.

When The eyes are almost closed the lens is stopped down to a horizontal slit  this means that the resolution in the vertical direction is impaired while that in the horizontal direction is not affected so badly because the resolution of a lens depends on its aperture.  The menicus in the fluid produces a negative cylindrical lens which would  distort parts of  the image vertically but leave the horizontal image less affected.
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