How to Read a Prescription for Glasses

1.

Look at your prescription. Locate the headings appearing over the numbers, such as OS and OD. Note that these are Latin abbreviations in which OS, or oculus sinister, is the left eye and OD, or oculus dextrus, is the right eye. Know that the abbreviation OU means "both eyes."

2.

View the numbers below the abbreviations. Note that lower numbers indicate better eye health. The higher the number, the worse the eyesight and the more vision correction is needed. These numbers measure the level of strength in the lens your eye requires and are measured in a unit called diopters, abbreviated "D." Look next to the number for a plus or minus sign. A plus sign indicates farsightedness and a minus sign indicates nearsightedness.

3.

Look to see if three numbers appear instead of one, indicating an astigmatism. A glasses prescription for someone with astigmatism has three additional notations: S, C and A. Read the abbreviation S as described in step 2, indicated nearsightedness or farsightedness. Read the abbreviation C and its corresponding number as a measurement in diopters of the astigmatism, in either a negative or positive amount. Read the abbreviation A as where the astigmatism occurs in your eye, as a measurement between 0 and 180 degrees.

Reading your glasses prescription is not always easy if you are unfamiliar with the terms and abbreviations of the field. However, knowing how to read an eye prescription can be useful in the event you need to replace missing or broken glasses, and serves as general knowledge that can be used to assist family and friends.