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Eye and Vision Care

When do you need new glasses?



Every time I get my eyes examined I am given a new prescription and told I need new glasses. Of course, this place also sells glasses. I never feel like there’s anything wrong with my current glasses.

If I compare my latest prescription with my previous one, is there a way to determine how much of a change in the numbers/corrections is significant enough to warrant purchasing new lenses? Thanks.


I can understand your frustration if you are told you need a new prescription each time you go to your eye doctor. As a practicing optometrist, I have come across this question/complaint many times.

From the patient's perspective, an increase or change in prescription may be viewed as an attempt by the doctor to sell a new pair of spectacles, just to make a sale. Other times the patient has concerns that the prescription will "make their eyes weaker," therefore they do not want to change their prescription.

Your recent experience:
If you felt that your current glasses were functioning pretty well for you, then you do not necessarily need to purchase new spectacles. Your eyes will not get worse if you don't get new glasses. If your vision is somewhat blurry through your current glasses though, it would make sense to change the prescription.

From the doctor's perspective, there may have been a decrease in visual acuity when you entered the clinic with your previous spectacles. He/she may have found an increase in the prescription which would sharpen your visual acuity and therefore he/she needs to make that recommendation.

It is hard for an untrained individual to quantify a change just by comparing the numbers on your previous two prescriptions. One way you could possibly compare for yourself, is to look at the sphere power and compare the numbers there. (I would say a change of 0.50 or more would be significant.)
With the cylinder power a change of 0.50-0.75 would be significant. The last number (Axis) is difficult to quantify as it is dependent on how much cylinder power is present.

Hopefully this helps, and remember, if you seem happy you do not necessarily need to fill a new prescription.

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Response by:

Aaron  Zimmerman, OD, MS Aaron Zimmerman, OD, MS
Clinical Associate Professor of Optometry
College of Optometry
The Ohio State University