How and Why To Change Bifocal Prescription Into A Single Vision Prescription!

by admin on 21/05/2009


Bifocals.  Just the word sends those who don’t know any better into a frenzy about the overall appearance they may have if forced into wearing them and others go crazy thinking that they are only for old people or that they are extremely thick.  All of these ideals are only imaginary.  Today’s bifocal are as thin as any other lens, and they come in all forms – round, blended, D or FT28, 35 segments…you name it, more than likely, an Optician can find what a patient needs.

What if, however, a person really doesn’t want nor feel that they need a bifocal?  Well, sometimes, they are correct.  Depending on their lifestyle and cares, many times that bifocal can be replaced by single vision lenses.  An example of this would be if a patient’s prescription is as follows:

OD: -0.50 sphere

OS: -0.25 -0.25 x 172

Add:  1.75

Clearly, the distance prescription (OD & OS) is 20/30 or better when it comes to visual acuity, therefore, there is no need to even use glasses for distance vision as there is little correction to obtain optimal vision.    However, as far as the add or bifocal reading power, there is a need for correction in the near vision.  In this example, the patient would prefer to not use bifocals as she sees clearly when driving and things of that nature, but most of her problem comes from reading.  On top of that, she doesn’t want to spend the extra money if she doesn’t need to even have distance vision inside the bifocal.

Surprise!  The patient can save money and only use her glasses for when she needs them most…reading.  In order to change the prescription to a single vision from a bifocal prescription, simply use mathematics – algebra.

OD: -0.50 sphere

OS: -0.25 -0.25 x 172

Add:  1.75

Simply add the bifocal power (+1.75) to the sphere powers.  The result is as follows:

-0.50 + 1.75 = OD: + 1.25

-0.25 +1.75 =  OS:  +1.50 -0.25 x 172 (The cylinder power and the axis always remain the same!)

Now the patient can save money while feeling better about her overall wear when it comes to eyeglasses.

Again, this is only one reason as to why an Optician may feel it best to change a prescription to single vision.  Other reasons may exist, and it is up to that eyewear professional what is needed for that particular patient.  If, however, there is an issue or questions with any changes, Opticians should always contact the prescribing physician.

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