| This is the distance between the back surface of the lens and the front surface of the eye. If the distance varies between the eye examination and the frame that is chosen then it may be necessary to adjust the power of the lenses prescribed to compensate for this variation. The higher your prescription the more critical this measurement is and the more critical you see a qualified dispensing optician who is able to make the compensation. The measurement is also required when ordering tailor-made varifocals and other state of the art lenses. |  |