Understanding Eye Prescriptions

An eye prescription may include any of the following abbreviations:

  • OD: oculus dexter (right eye)
  • OS: oculus sinister (left eye)
  • OU: oculus uterque (both eyes)
  • SPH: the strength of magnification in the lenses
  • CYL: cylindrical correction, or the amount of lens power needed to correct astigmatism
  • AXIS: indicates the angle of astigmatism correction
  • ADD: addition, used for bifocal and multifocal lenses
  • PD: Pupillary Distance Pupillary distance (PD), more correctly known as interpupillary distance (IPD) is the distance in millimeters between the centers of each pupil. Our Virtual Try on automatically measures your PD be sure to match it with your prescription for the correct fit and lens.


  • Mild: +/-0.25 to +/-2.00 
  • Moderate: +/-2.25 to +/- 5.00
  • Severe: +/- 5.00

It is highly recommended that you add High Index lens for moderate to severe power strength for your eyeglasses. This allows the lens to look thin for a much better look and feel of your eyeglasses or sunglasses.

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