In dark room when you squint your eyes you can see lines (mostly vertical and close to vertical) coming from light sources. What is an exact reason of that phenomenon?
If I’m understanding you correctly, I think it’s due to diffraction effects from the edges of your eyelids. The lines are vertical, because your eyelids are horizontal.
I assume you’ve never had cataract surgery, right? Ever since my surgery, I see rays coming out of all lights or bright areas, at specific angles. I dread driving at night, especially when it’s raining, and most especially in the Christmas season.
I bet it isn’t diffraction, but rather refraction in the meniscus of tear liquid that would be at the edge of your eyelid. To see what the diffraction would look like, make a little slot out of paper with a rectangular spot cut out, and hold that up close to your eye while your lids are wide apart.