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How do I read my prescription?Updated a year ago

Your prescription is made up of different parts that each play an important role in creating your Prescription lenses! Below is a brief overview of all of those prescription parts and their role. For any specific questions about these measurements or entering your prescription, the Fuse Prescription team is here to help! 

Oculus Dexter (OD) and Oculus Sinister (OS)

Oculus dexter means right eye in Latin and oculus sinister means left eye. Oculus uterque is both eyes and if you don’t see any of those then the prescription might say RE for the right eye and LE for left.

Sphere (SPH)

The prescription of your lens power measured in diopters (D) is called the sphere. If this number has a minus sign (-) in front of it, then you can see up close but need correction to see far away. If it has a plus sign (+) then it means you can see at a distance but need help seeing things up close. The sphere value is measured in decimals because it is measured in diopters.

Cylinder (CYL)

People with astigmatism that needs to be corrected have a cylinder value. The cylinder is the amount of lens power for astigmatism, like the sphere, it is also measured in diopters. If it is negative it corrects nearsighted astigmatism and if the number is positive it corrects farsighted astigmatism.

Astigmatism is a defect in the eye caused by a deviation from spherical curvature which results in distorted images. To compensate for this deviation of the spherical curvature, a cylinder power needs to be added in addition to that of the sphere.


Axis is another number you might see when you have astigmatism. The axis is the lens meridian that contains no cylinder power to correct astigmatism. The actual number that is written on the axis is the lens meridian that is 90 degrees away from the meridian that contains the cylinder power. Sometimes, an “x” is written in front of this number.


For progressive lenses or bifocals, you will need an add value on your prescription. The add value is the added magnifying power applied to the bottom part of your lenses that help you see things that are closer to you.


Measured in prism diopters or p.d., prism or prismatic power is the number used to compensate for eye alignment problems. The direction of this prism is based on the relative position of the base, which is the thickest edge. The four prism directions are base up (BU), base down (BD), base in (BI -- towards the nose), and base out (BO -- towards the ear).


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