How to Make Sense of Prescriptions for Spectacles

After your appointment with an eye doctor, or ophthalmologist, you will be given a prescription, similar to the way a physician writes a prescription for medication, for eyeglasses if you need some. You can choose to purchase your eyeglasses from the ophthalmologist, if he provides this service, or take the prescription to another retail location or go online to purchase your spectacles. Your new spectacle prescription includes four parts: 1) which eye; 2) the prescription power, which also indicates near- or farsightedness; 3) degree of astigmatism and 4) reading or bifocal adjustments. The format of the prescription is consistent for each eye although prescriptive needs may vary between each eye.



A typical eyeglass prescription, which can be hard to interpret without a few pointers, looks something like this:

OD -2.25 +1.25 x 90

OS -1.75 +1.00 x 45

OU +1.50

Instructions

Interpreting Spectacle Prescriptions

• 1

  Look at the letters at the front of each line of the eyeglass prescription. OD stands for the Latin phrase oculus dextrus and indicates the right eye. OS stands for oculus sinister and indicates the left eye. OU stands for oculus uterque and refers to both eyes together.

• 2

  Locate the first number in the prescription string on each line. This is known as the spherical portion of the prescription and can be positive or negative. If the number is negative, it indicates nearsightedness. A positive number indicates farsightedness. The number itself stands for the number of diopters that your eye varies from zero or normal. Diopters indicate the amount of focusing power required by the lens to correct vision to normal.

• 3

  Locate the second number on the OD and OS lines. This is known as the cylinder and also can be positive or negative. This number indicates the power correction needed to compensate for the astigmatism. Both this number and the number addressed in Step 4 are used to indicate if you have astigmatism and the amount of correction needed. If you do not have astigmatism, these numbers will not appear on your prescription.

• 4

  Locate the third number on the OD and OS lines. This number follows the "x" and is known as the axis and indicates the orientation of the astigmatism in a range from 0 to 180 degrees.

• 5

  Locate the prescription string marked OU. This measurement indicates a vision correction that is equal for both eyes. A person who has the same focus power for both eyes may get a prescription from an ophthalmologist that only says OU -2.25. For the above example, the OU prescription could indicate the patient requires a separate pair of reading glasses with both lenses at a focusing power of +1.50. Alternatively, the OU prescription line could indicate the addition of bifocal lenses of a focusing power of +1.50 to be placed on both the right and left lenses.