When your eye doctor hands over an eye prescription, you can be bogged down by all those numbers and abbreviations on the tiny card. Knowing how to read your eyeglass prescription will be of great help.

Click here to view interactive prescription

Figuring Out The Terms On The Eyeglass Prescription

OD, OS and OU

There will be certain numbers under OD, OS and OU columns which are basically Latin abbreviations.–

  • OD (oculus dextrus) means the right eye,
  • OS (oculus sinister) means the left eye
  • OU (oculus uterque) means ‘both eyes’

This is the traditional way in which prescriptions have been written for long but now some doctors have simplified your life and started using left and right.

Sphere (SPH)

SPH tells you the power of the lens correction (in diopters) you would need for perfect vision. The further the number from zero, the more high power lens you would need. A plus sign in front of the number shows that you are farsighted while a minus sign means that you are nearsighted. Farsighted people see things at a distance more easily than they see things up close which appear blurry. Nearsighted people see objects in the distance as blurry and out of focus.

Cylinder (CYL)

When you are suffering from astigmatism, you will notice three numbers in your prescription written in the general form SPH x CYL x Axis. CYL measures the power of the lens needed to correct the astigmatism you have and can be a positive (farsighted astigmatism) or negative value (nearsighted astigmatism).


The axis value automatically comes in when you have a cylinder power. Axis can range between 0 and 180 degrees and show the orientation of astigmatism.


Aged adults suffering from presbyopia have to opt for multifocal lenses. To correct the near vision, this Add value specifies the magnifying power to be added to the distance prescription in the lower half of the lens. Add power is similar for both eyes and ranges between +0.75 to +3.00 D.

Prism and Base

If you have eye alignment problems, Prism is added to your prescription in the form of metric units. Base would show the location of the thickest edge of the prism which can be up, down, in or out.

A Sample Prescription – Click here to view interactive prescription

OD -3.00 +1.00 add 0.5 p.d. BD (base down)
OS -2.00 -0.50 180 +1.00 add 0.5 p.d. BU (base up)

In this Case the right eye suffers from nearsightedness (myopia) for which a -3.00 SPH is prescribed. The left eye suffers from astigmatism which is why the doctor prescribes

-2.00 D sphere for nearsightedness (myopia) plus -0.50 D cylinder for the correction of astigmatism and the cyl power has its axis at the 180 meridian.

+1.00 D add power is added for the correction of presbyopia for each eye while a prismatic correction of 0.5 prism diopter is added in each eye, down for the right eye and up for the left eye.

Your Eyeglass Prescription Belongs To You

Your eye doctor will give you a copy of your eye prescription (mandated by law) so that you can purchase discount prescription glasses from anywhere you choose to. Be sure to ask your optometrist when they forget to give you a prescription glasses mini card.