Convert Bifocal to Reader Strength

Most of us know the top portion of a bifocal lens is adjusted for distance vision, while the bottom portion (the bifocal segment) is used for near vision.

The problem is, bifocal glasses can be expensive. And a good way to save money is to have "single vision" prescription glasses made for distance and get a pair of quality close-up glasses (or reading glasses) for activities that require-close up vision like reading, writing, or working on computers.

But how can you decode the formula your eye doctor uses to communicate with his lens lab? And what can you do with your decoded result? It's simple! And we're going to let you in on the secret now.

Locate Your Prescription Details: Look at the prescription for your current eyeglasses. You’ll need the sphere (SPH) value for each eye and the “ADD” value. That value indicates the additional magnification needed for close-up vision.

Your eye doctor and his lab both know your right eye's "secret code" is OD. And your left eye's "code" is OS. Now, you know, too!

Perform the Calculation: For each eye, add the “ADD” value to the sphere (SPH) value. That simple addition will render the reading glasses prescription, or the diopter strength.

For example, if your right eye, OD, has a sphere value of -1.00 and an ADD value of +2.50, the diopter strength, or reading glasses prescription, for your right eye would be +1.50.

Now, perform the same calculation for your left eye, or OS.

Most people have a slight difference between their right and left eyes, but making a "half in between" compromise works well for almost everyone who prefers to economize and wear "ready-made" reading glasses (or to not look "dorky" in bifocals)! Ready-made reading glasses have the same lens strength in each eye. 

Wonder what "OS" and "OD" mean? OS stands for “oculus sinister.” and your right eye is OD, or “oculus dexter.” These are Latin terms used routinely in optometry and ophthalmology.

Now you can decode your eyeglass prescription. And instead of buying the high-cost option of bifocals, you can switch to close-up with a good pair of quality readers. 

For example, take a look at these prescription quality breading glasses.

The material provided on this site is for informational purposes only. It is not intended to replace the advice of your eye care professional. Have your eyes examined regularly and always follow your eye care professional's instructions. If you experience any pain, discomfort, or visual distortion, consult your eye care professional immediately.

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