I have a peculiar vision abnormality. With or without one eye closed (either eye), I see a faint second image, shifted slightly above the normal image. It appears that when a ray of light hits the lens of my eye, it splits into two rays, one ray a fraction of a degree above the other one. This is not a diffuse blurriness as in nearsightedness, nor is it the double vision that you get from the two eyes not being coordinated with each other (because it happens with just one eye open). I once explained this to an opthalmologist but he offered no explanation. Since it's about optics I thought physics rather than biology. What could cause this?