If you’ve ever looked closely at your eye glass prescription, you’ve probably wondered how to make sense of all those numbers and symbols. In order to be interpreted worldwide, eyeglass prescriptions are written in a standardized format with common notations.

The first step to understanding your eyeglass prescription is knowing what OD and OS mean. They are abbreviations for oculus dexter and oculus sinister – Latin terms for right eye and left eye. Your eyeglass prescription also may have a column labeled OU. This term is the abbreviation for the Latin words oculus utro which means both eyes. On your eye glass prescription, the information for your right eye (OD) comes before the information for your left eye (OS). Eye doctors write prescriptions this way because when they face you, they see your right eye on their left (first) and your left eye on their right (second).

Your eyeglass prescription may contain other terms and abbreviations. These include:

SVD – Single Vision Distance, or glasses for distance only.

SVN – Single Vision Near, or glasses for reading only.

PD – Pupillary Distance meaning the distance between the centers of the two pupils between the eyes. This measurement is essential to designing glasses that are comfortable to wear.

Sphere (SPH) – The term “sphere” means that the correction for nearsightedness or farsightedness is spherical, equal in all meridians of the eye. This indicates the amount of lens power, measured in diopters (D), prescribed to correct nearsightedness or farsightedness. If the number appearing under this heading has a minus sign (–), you are nearsighted; if the number has a plus sign (+) or is not preceded by a plus sign or a minus sign, you are farsighted.

Eye Glass Prescriptions Part Two continued next week.