Knowledge about Eyeglasses Prescription

The abbreviations and numbers on your prescription may look unfathomable, but it's really a kind of medical shorthand-a professional's way of telling a laboratory what's needed to correct your vision. RIGHT EYE (OD) OD = Oculus Dexter in Latin, or right eye. LEFT EYE (OS) OS = Oculus Sinister in Latin, or left eye. BINOCULAR Binocular = both eyes. On your prescription, your pupillary distance may be a binocular PD (one number for both eyes) or a monocular PD (one number for each eye). SPH or RX SPH = Sphere or spherical correction describes the horizontal curve of your eye's lens. The sphere is assigned a positive (+) or negative (-) number between -20 and +10. And sphere is the lens power that it takes to focus an image on your retina correctly. A single-vision eyeglass prescription without astigmatism lists only SPH. CYL = Cylinder or cylindrical correction fine-tune for the astigmatism-the vertical curve of an eye-shaped more like a football than a sphere. Astigmatism is very common. The cylinder is a positive (+) or negative (-) number between -6 and +6. Your prescription may or may not have a CYL number. AXIS = the degree and direction of astigmatism. If you have a CYL number indicated on your prescription, you'll also have an AXIS measurement. It's a positive (+) number between 0 and 180, sometimes preceded by an "x". A single-vision eyeglass prescription with astigmatism lists values for SPH, CYL, and AXIS.