In order to calculate the lens power needed for each eye, please use the calculator below. The calculator uses the following equation to calculate diopter strength for each eye:
DIOPTER STRENGTH = 1/2 of the CYLINDER + SPHERE
As a rule of thumb, always round down to a diopter strength that is one step lower than the calculated value. For example, if the calculated diopter strength for the left eye is 5.0, round down to 4.5.
How to Interpret an Eye Prescription
Hover over the boxes in the prescription on the left to understand what each section is about.
The lens power prescribed to help you see more clearly.
OD and OS
- "OD" is the abbreviation for "Ocular Dexter" (Latin for your RIGHT eye)
- "OS" is the abbreviation for "Ocular Sinister" (Latin for your LEFT eye)
- If you see "OU" on your prescription, it means "Oculus Uterque" (Latin for each eye), so the same measurement applies to both eyes.
Indicates the prescription power, or how strong your lenses need to be to correct your vision. A minus sign means the prescription is for nearsightedness (i.e., myopia). A plus sign means the prescription is for farsightedness (hyperopia).
Denotes astigmatism, a condition where the cornea is irregularly shaped causing blurred or distorted vision. If your astigmatism is over 2.0, custom-made lenses may be more appropriate.
The Axis number describes the position of the astigmatism in your eye. It is not used to determine the lens power for your prescription swimming goggles.
Prism and Base
Prism is added to some prescriptions to compensate for eye alignment problems. Base refers to the thickest edge of the prism, which is also the direction toward which the prism redirects light. If you need Prism correction, custom-made lenses may be more appropriate.
This number is used for bifocals and is not used for calculating goggle lens strength.