Difference between revisions of Lens

Glasses are only perfectly tuned through their optical centers.  If your [[Pupillary Distance]], Pupillary height, or lens adjustment are off, you might not be looking through the optical center of the lens, and you are certainly not looking through the optical center when you look around instead of straight ahead.  The power of the lens will vary, and unintentional prism or cylinder can be introduced.  You may also not be wearing the lens at the intended vertex distance, affecting the effective power of the lens.  The stronger the lens the more of a difference this makes.