How To Read a Prescription

How to Read an Eyeglass Prescription

An eyeglass prescription is written in a standardized format with standardized notation so that it may be interpreted worldwide. Please refer to the below example. On the DISTANT section of the prescription, note the numbers -2.00 -1.00 18

The first number (-2.00) tells us the spherical refractive error (farsightedness or nearsightedness). In this case, because there is a minus sign in front of the 2.00, this patient is nearsighted. A plus sign would indicate farsightedness.

The second number (-1.00) is the astigmatism. If there is no astigmatism, we generally write the letters DS or SPH after the first number. This makes it clear to the optician that we didn’t just forget to write in the astigmatism.

The final number (180) is the direction (AXIS) of the astigmatism. Astigmatism, which means a football-shaped eye, can be measured in any direction around the clock. We use the numbers from 90 to 180 to indicate the orientation of the football shape.

There may be additional numbers in a prescription. For instance, if the basic prescription is followed by a small number with a superscript (1^) it indicates prism correction. There may be more than one set of prism numbers for each eye.

Lastly, there may also be numbers in the ADD area denoting the amount of near reading strength needed for reading (progressive). They usually range from +0.75 to +3.00, depending on age and visual need.

You might also see the letters OD and OS in front of a prescription. These let us know which eye each string of numbers is for. OD (Oculus Dexter) stands for right eye and OS (Oculus Sinister) for left eye, while OU (Oculus Uterque, Oculus Unitas or Oculus Uniter) means both eyes.

There are many different prescription needs; not all prescriptions will have a CYL-cylinder, AXIS, PRISM, or ADD. CYL and AXIS are needed to correct for astigmatism. PRISM is needed to correct for certain eye functions and double vision. ADD is needed to correct for near accommodation.

If you have questions about the accuracy of your prescription, please contact the prescribing eye doctor's office for clarification before placing your order.

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