THE 411 On reading prescriptions

If this is your first time with a child in glasses - you may not know where to start, let alone how to read a glasses prescription.

By learning how to read your child’s prescription, parents can better understand their child’s vision. And having a basic understanding of the eye prescription comes down to learning the layout of a prescription and the meaning of each number and character.

Understanding the lay of the land

Prescription charts typically have two rows labeled one for your Right Eye (O.D)  and one for your Left Eye (O.S) 

You'll sometimes see the prescription O.D. and O.S.  which are abbreviations for Latin words that mean Right eye and Left eye.

From left to right on the top row of the prescription you will always find SPH, CYL, and AXIS. 

It is important to note that there may not be a value entered for these categories, if that is the case there is no correction needed.

SPHERE ( often abbreviated as “sph”) 

SPH stands for spherical power and describes the degree of nearsightedness or farsightedness. 

A positive value, or a prescription with a plus-sign (+), means that your child is farsighted.  If you see a negative value (-) that means your child is nearsighted. 

In general, the further away from zero the number on your child's prescription, the worse your child's eyesight and the more vision correction they need.  

T he higher the number (ignoring the plus or minus), the stronger the prescription.

  • + : farsighted, or longsighted prescription: hyperopia.
  • – : nearsighted, or shortsighted prescription: myopia.
  • 0, Pl, or Plano : no error

CYLINDER ( often abbreviated as “CYL”) 

Cylinder is the measure of astigmatism - simply put that the front of the eye has less of a perfectly round shape. 

A person with astigmatism does not see clearly either at distance or at near which can result in blurry vision & results oftentimes with headaches.

For some prescriptions there will be no astigmatism correction for one or both eyes.  Your eye doctor may just write the sphere power alone, or may use abbreviations like sph (“sphere”) or DS (“diopters sphere”).

Please note : often times MDs use plus (+) and ODs use minus (-) for the CYL value.  So if you see a plus (+) in the CYL value this means that a conversion needs to take place and the SPH and AXIS values will be affected - nothing to worry about as we will do this for you but we just like to state this so parents can get a good understanding.


If you do have a CYL number you will also have an axis number.  

The axis indicates the orientation of astigmatism, measured in degrees from 1 to 180.

Other details listed on prescription 

To the right of AXIS you may find ADD, PRISM, and P.D. 

ADD stands for addition and is used with multifocal lenses (ie bifocals).  If your child needs bifocals, you will likely see a number here.  ADD is additional magnification which helps with vision at close range.  Unfortunately, we cannot fill prescriptions that require a bifocal. If you see this on your prescription, please contact us at and we will make a recommendation for you.

PRISM is used to help people with muscular imbalance in their eyes.  Prim helps to reduce eyestrain and correct double vision.  

Please note : We are able to fill prism within a certain range however, there is an additional fee for prescriptions that require a prism.  Our team will contact you directly if this is listed on your child's prescription.

P.D., or Pupillary Distance, is the distance between the centers of the pupils, which is used to position the lenses in frames. A PD measurement is required for us to fill your prescription order.  

If you do not see a PD listed on your child's prescription, simply ask your optician; they should have your PD on file.  Or you can also measure your PD yourself using our easy measuring tool.

Pupil distance can be measured in two ways :

Binocular which is a pupil-to-pupil measurement, this type of measurement will be between 42-60 mm for most children
Monocular which is a per-eye measurement from the pupil to the middle of the face -
 example : 25/24.5 - the first number (25) is for the right eye (O.D.) and the second number (24.5) is for the left eye (O.S.) - total these together to get 49.5 binocular

still have questions?

please contact us at and we will be happy to help answer any questions you may have regarding your child's prescription & make any lens recommendations for you!