How To Convert Your Contact Lens Prescription To Glasses Prescription

Yes there are several, like Alcon’s:http://www.virtualconsultant.alcon.com/lens_power.jsp

A quick way to estimate is to look at any prescription over -4 diopter, and add +0.25 diopters for every two diopters of increase:

4.00 D +0.25 D
6.00 D +0.50 D
8.00 D +0.75 D
10.00 D +1.00 D
12.00 D +1.25 D
14.00 D +1.50 D
16.00 D +1.75 D

So a -4.00 glasses prescription is roughly equal to a -3.75 contact lens prescription.

You can do the same for astigmatism correction, though it only becomes relevant if the glasses astigmatism is at least -0.75 to -1 diopters (otherwise combine cylinder and spherical from the glasses prescription for the contact lens).

In practice this will vary, often towards requiring a slightly lower contact lens equivalent than the formula suggests.

Also bear in mind that contact lenses are best used after a proper fitting is done at the optometrist office, before embarking on future adjustments to the prescription on your own.”

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(The full thread is here).  Many lens manufacturers and distributors provide formulas on their sites to convert to contact lenses, and they do tend to vary from one site to the next.

The usefulness of those calculators are limited for many of you in the process of rehabilitating your eyesight.  In most cases the question for the purpose of vision improvement goes in the opposite direction.  You want to convert the other way around: from contact lenses to glasses – since for the most part, you want to be using glasses instead of contact lenses for close-up.  

Contact lenses in combination with hours of looking at close-up objects are a recipe for trouble, as their combined effect on tear fluid along with the reduced blink rate create more eye strain (less tear fluid also tends to compromise vision clarity).  

For distance vision contact lenses do provide a better visual, and I often recommend them for extended outdoor use (and focus pulling), especially for high myopia cases.   So, contact lenses good for distance, but not recommended for close-up!

If you are switching to a differential prescription for reduced close-up strain for the first time, the conversion adds a bit to the overall challenge of determining an ideal prescription for you.  Not only do you need the reduction for close-up, but also considering the change from contact lenses to glasses.  This is just one more reason to start with the myopia calculator instead of your existing lens prescription.  

I hope this helps, if you are looking to optimize your prescription use.  If you have questions on this subject, just post in the support forum for further clarification.

Enjoy healthy eyesight today!