Astigmatism
Astigmatism is commonly caused by irregularity of corneal surface. The surface of the cornea is more like a ruby ball than a spherical football with one meridian steeper or flatter than the other. This irregularity of corneal surface causes blurred or distorted vision.

Two focal points are formed instead of one focal point causing blurred or distorted vision.

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Do I have astigmatism or double vision?