Understanding your Eyeglass Prescription

Understanding your Eyeglass Prescription


You have probably seen an eyeglass prescription and have wondered what those series of numbers and letters are for, or what the numbers mean. Allow us to break them down, so you can understand your prescription better.


  • OD and OS

These are abbreviations for Latin phrases Oculus Dexter (OD) for right eye and Oculus Sinister (OS) for left eye. Sometimes, you can also see Oculus Uterque (OU), which means both eyes. Although, some doctors now use RE (right eye) and LE (left eye).


  • Sphere or SPH

This tells the amount of lens power needed to correct your myopia (nearsightedness) or hyperopia (farsightedness). Measured in diopters (D), a minus (-) sign indicates you are nearsighted and a plus (+) sign says you are farsighted.


Farsightedness means you can see far objects clearly. Those with a severe case of farsightedness have blurred vision at any distance, near or far. Nearsightedness, on the other hand, means that you can see objects that are close to you clearly and those that are farther away are blurry. When you are nearsighted, your eyes are longer than usual, and if your eyes continuously grow longer, it is considered progressive myopia/nearsightedness.


  • Cylinder or CYL

This is the indicator of the amount of lens power needed to correct your astigmatism. Astigmatism is a condition when your eye grade is higher on one axis and lower on another axis location. The difference between the two eye grade in one eye is the grade of your astigmatism.  


When you have astigmatism, the shape of your cornea is uneven. This causes you to have blurry, distorted vision.


  • Axis

The cylinder power always comes with an axis value. The axis tells you which part of your cornea has the astigmatism, and is defined with a number from 1 to 180. Determining the axis value will help people with astigmatism see better.


  • Add

If you are wearing bifocal or progressive lenses, you will see a number written under Add. It pertains to the amount of additional correction your eyes need to focus at near distance. Applied to the bottom part of the lenses, it aids the reading vision of people with presbyopia. Whether or not there is a plus sign (+), it will always be a positive number.


Presbyopia occurs in people over 40 years old, wherein they are having a hard time reading text in their mobile phones, books, or even restaurant menus. However, there are people who develop presbyopic problem before they turn 40.


  • Prism
    It is a special type of correction for people with alignment problems or double vision. Measured in prism diopters (PD), it fuses to images together so the patient can only see one image.
  • PD or Pupilllary Distance

It is the distance between the two eyes, measured at the center of each eye pupil. This is measured, so that the center of the eyeglass lenses will coincide the center of your pupil or eye.


Remember that an eyeglass prescription is different from a contact lens prescription. Contact lenses are placed directly on the eye, so these need specific measurements and brands to ensure you can see clearly and comfortably. And because your vision can change over time, it also helps to get checked at least every year to make sure your prescription is upgraded and your eyes are healthy.