# Guide:Reducing differentials

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## Simple way

The EndMyopia process will probably involve a lot of trial and error. Bearing this in mind, Jake recommends you reduce from your glasses prescription by about 1.25 diopters.[1] This will depend on the distance you work from the screen, so reduce it by less if you work farther from the screen. Between 1-2 diopters is a good range - anything more than that and you'll probably want to double check it's a good idea.

## Complicated way with math

The base point is an emmetropic eye with 20/20 vision.

Everyone has a different level of myopia, and depending on this you can calculate the required amount of correction to just see the object, based on how far away it is.

Firstly, find out the distance from you to the object. In plain English, how far away is the object in centimetres?

Type in the cm value you get into EndMyopia diopter calculator to figure out the difference between your full strength prescription glasses, and what you actually need to see the screen.

Then, take the difference and subtract it from your full strength prescription glasses. Voila! you have a differential prescription.

### Example

Suppose you have OD/OS -4.25/-3.25, and you see, or want to see your monitor 60cm away from where you sit.

Go to the calculator, and enter in 60cm. The result is -1.75. Subtract this value from both of your eyes (be careful with negative numbers).

${\displaystyle OD(righteye):-4.25-(-1.75)=-2.5}$

${\displaystyle OS(lefteye):-3.25-(-1.75)=-1.5}$

So, you should use OD/OS -2.5/-1.5, if 60cm is the main distance you perform up-close activity. Simple!

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