How to Read Your Eyeglass Prescription

How to Read Your Eyeglass Prescription

You may not understand how to read a prescription for spectacles if you are wearing glasses for the first time, let along knowing what does it means. Therefore, we have composed this guidance to help you learn about your prescription for spectacles so that you can easily order your new pair of prescription glasses online.
How to Read Your Eyeglass Prescription

What do OD and OS mean?

They are abbreviations for Oculus Dexter and Oculus Sinister, and these are the Latin terms for the right eye and the left eye. Your prescription may also contain an “OU” column. This is the abbreviation for the Latin term oculus uterque, which means “both eyes”. However, some doctors may also use RE (right eye) or LE (left eye) to replace O.D. and O.S.

Sphere (SPH):

This abbreviation is used to indicate whether the patient is myopic or hyperopic. If the mean of spherical diopter is displayed with a (-) mark, the patient is myopic; if the mean of spherical diopter is displayed with a (+) mark, the patient shall be hyperopic.

Cylinder (CYL)

CYL indicates the amount of lens power for astigmatism. If this column is left blank, you have either very slight astigmatism or no astigmatism at all, so you don’t need lenses for correction.
If the mean of cylindrical diopter is displayed with a (-) mark, you have myopic astigmatism; if the mean of cylindrical diopter is displayed with a (+) mark, you have hyperopic astigmatism.


Sometimes, it may also appear as “X”, indicating the direction of astigmatism. The integer varies from 0 to 180 indicates the astigmatism direction, of which 90 stands for the vertical meridian and 180 stands for the horizontal meridian of eyes.


ADD indicates that magnifying power is added to the lower parts of multifocal lenses. This is for the correction of presbyopia so that the patient can focus on close objects. It is designed for reading, since progressive and bifocal lenses can provide a magnifying power.

Pupillary Distance (PD)

PD is the distance from one center of a pupil (central black spot of the eye) to the other in millimeters. People making glasses use this “pupillary distance” to decide the optical center of lenses. If the positioning of optical centers is wrong, the glasses will make your eyes feel uncomfortable. If you cannot find PD on your prescription, please ask your optician directly. Or you can also use our simple measuring tools to measure your PD by yourself, here: How to Measure Your PD(Pupillary Distance)? 


The prism number stands for the prism power adopted for dioptometry to compensate for any focusing problem of your eyes. This can help patients with unbalanced eye muscles. Prim can help to alleviate asthenopia and correct diplopia.

Now you have already known the prescriptions for your glasses, then you need to select the right prescription lenses according to your prescription. Please refer to this article: Types of Prescription Glasses

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