HOW TO READ YOUR PRESCRIPTION
Your eyeglass prescription is typically written with 2 lines of numbers. Top line is power for Right Eye, second line is Left Eye.
OD – Right Eye: usually the top value in an eyeglasses prescription chart. OD is a latin abbreviation for oculus dexter, which means "right eye."
OS – Left eye: usually the bottom value in an eyeglasses prescription chart. OS in Latin is oculus sinister, or "left eye."
The powers for each eye are specified by Sphere, Cylinder and Axis.
SPH – Sphere: the horizontal curve of the eye’s lens; (+ or – number between –10 and +10) Also called your prescription’s power, this is how strong your lenses need to be.
CYL – Cylinder: indicates astigmatism; (+ or – number between –4 and +4 ) If you have a number for CYL, you, like many glasses wearers, have astigmatism. This simply means the vertical curve of your eye is shaped more like a football than a sphere.
AXIS: Indicates the degree and direction of astigmatism; (+ number only between 1 and 180) Often this number will be proceeded by an x. You will not have an AXIS if you don’t have a CYL.
PRISM: The majority of glasses wearers will not have a PRISM measurement. If you do, you have a more difficult glasses prescription that requires an optician’s expertise.
ADD: Only for bifocals/progressive lenses (+ number only, usually up to 5.00) How much magnifying power you need in your bifocal/progressive lenses.