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Understanding your Eye Glasses PrescriptionHow to translate this eye glasses prescription into magnifier strength? Sharpen your pencil, get your calculator and let’s get to it..
Your prescription will have numbers for the right and left eyes. It will probably be written like this: R +1.00/-1.00 x 90 L +1.25/-0.50 x 90 Add +1.00
What do the numbers mean?Let’s start with the right eye. The first number is the Sphere (sph).
This is a measure of your long-sightedness or short-sightedness. This could be any number plus or minus or even zero (also called plano). The numbers go in 0.25 steps. The second number is the cylinder (cyl).
This is a measure of your astigmatism which is how egg shaped your eyes are. This could be any number plus or minus or even zero. The numbers go in 0.25 steps. If you have no astigmatism because your eyes are as round as tennis ball, then this will be left blank. The third number is the axis.
This relates to the angle of the astigmatism. This will be a number between 5 and 180. The steps are in 5’s ( though occasionally the steps are 2.5) The Add. This is the extra help, in addition to your distance prescription that those maturing eyes need.
How does this translate to magnifiers?1 Take the second number the cyl power and half it. In our example -1.00 becomes -0.50. 2 Add the halved cyl power to the sphere power. Add -0.50 to +1.00 answer +0.50 You have now got a number that Optometrists call the best vision sphere. 3 Add the best vision sphere to the Add power. Add +0.50 to +1.00 answer +1.50
The good news is that it doesn’t play a part in this eye glasses prescription calculation.
1 Take the cyl power and half it. In our example -0.50 becomes -0.25 2 Add the halved cyl power to the sphere power. Add -0.25 to +1.25 answer +1.00 3 Add best vision sphere to the add power. Add +1.00 to +1.00 answer +2.00 Now you have changed the eye glasses prescription into a strength for magnifiers. R +1.50 L +2.00
I thought you said that magnifiers were equal in both eyes?That is the compromise you will be making. Since the magnifier powers are equal you could split the difference and get a +1.75 right and left if that is available. Usually they come in 0.50 steps. Or I’d suggest +1.50 on the basis of using the weakest strength to see clearly.
How successful would these magnifiers be for you?They would probably work well for 5 min bursts of reading. Any longer than that and you may suffer eye strain and fatigue. That might be fine depending on what you are doing. How long are you going to spend looking up a phone number, composing a text message or looking at a menu? Take a look at my
rule of thumb
to work out if magnifiers are for you.
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