Future Optometrists

  POWER SPECIFICATION OF OPHTHALMIC LENSES                     F=1/FL where F is focal power of lens FL is the focal length of the lens in meters Power specification of Ophthalmic lenses can be based on methods are:     1. APPROXIMATE POWER      2.BACK VERTEX POWER      3.FRONT VERTEX POWER      4.EQUIVALENT POWER      5.EFFECTIVE POWER 1.APPROXIMATE POWER     Approximate (close to actual)      Algebric summation of front surface power and back surface power. F a =F 1 +F 2      Where F 1 is front surface power, F 2 is back surface power as given by curves of                respective surfaces, measured by lens measure watch.      Respected material index. Lens thickness not considered in this method. 2.BACK VERTEX POWER    ...