How to Read My Eye Glass Prescription
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, which are 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, or 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 or 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.
Cylinder (CYL). This indicates the amount of lens power for astigmatism and represents the difference in the greatest power of the eye and weakest power of the eye, usually separated by 90 degrees. If nothing appears in this column, either you have no astigmatism, or your astigmatism is so slight that it is not necessary to correct it with your eyeglass lenses. The number in the cylinder column may be preceded with a minus sign (for the correction of nearsighted astigmatism) or a plus sign (for farsighted astigmatism). Cylinder power always follows sphere power in an eyeglass prescription.
Axis. If an eyeglass prescription includes cylinder power, it also must include an axis value, which follows the CYL power. The axis indicates the angle (in degrees) between the two meridians of an astigmatic eye. The axis is defined with a number from 1 to 180. The number 90 corresponds to the vertical meridian of the eye, and the number 180 corresponds to the horizontal meridian.
Add. This is the added magnifying power applied to the bottom part of multifocal lenses to correct presbyopia. The number appearing in this section of the prescription is always a plus power, even if it is not preceded by a plus sign. Generally, it will range from +0.75 to +3.00 D and will be the same power for both eyes.
Prism. Only a small percentage of eyeglass prescriptions include prism. It is often prescribed to displace the image in a certain direction for patients with eye alignment problems such as crossed-eye (strabismus) or other eye muscle or focusing disorders.
If you are due for new eyeglasses in Tucson, contact Eye Associates of Tucson at 520-888-6600 or website to schedule an eye exam with Our doctors.