The EM Template (or how to get all the necessary info summarized in an excel workbook)

Hi again myopic folks!

After reading this topic:

I thought that instead of working with a pencil and a piece of paper or use the phone calculator each time one would like to convert this to that, it would be cool to have some sort of an input-output template, in which one would type the measurments and/or the current Rx and it will display what you should have. Needless to say that above all, the baseline should be what one can see / one has measured in cm, this is just sort of a backup that would eventually confirm that your chosen differentiasl/normalized/whatever is in the right direction, or that perhaps one is reducing too fast, or should check for eye strain/think about increasing the power. Its intention is not to be a thing to blindly follow (if I can crack such joke), but just use it as a side tool combined with other things (such for instance, Varakari’s vision log tool, which I consider a must).

Here are some screenshots of the draft:






Basically, write down the data in the cells coloured in white and the rest will be calculated. The rows displayed in darker blue from the vertex distance refers to the most common vertex distance that one should have (something between 10 to 20 mm -ish).

Here is the file to be downloaded if one wants to play a bit with it (expires in 1 week, in case it’s down, let me know and I will reupload it):

Maybe the best way to work together with other users would be to dump all the data in one google sheet, but as I don’t have a gmail account (I don’t like the big G…) I would need to find some other equivalent opensourced gdocs. I will include the link after having that ready.

At the moment Viceroy Sam, anuw and AznDudelsOn were helping me in the Discord server (and again, many thanks to them :pray:), but maybe I could get even more support here at the forum as I’m kind of stuck at the moment :expressionless:

These are the formulas I would like to get and I couldn’t figured them out 100% yet:

  1. How to get an approximate differential spheric power based on the distance to screen
  2. How to convert from Glass to Contact Lens
  3. How to convert from Contact Lens to Glass
  4. How to estimate a probable vertex distance based on the current prescription of contact lens and glasses

About nº1: Calculating the differentials

The given formulas (the source was the thread linked at the beginning of this post) don’t seem to work for me. As for the chosen distance they don’t seem to match what I tested with the trial lens kit (too underpowered?).

Also, would be interesting to have the option to include, ignore or convert to SPH the astigmatism for the differentials? What do you think?

About nº2: How to convert from Glass to Contact Lens

I would say that this is not working for my left eye (-8.00, -0.25, 20º), as it doesn’t seem to be paired with my current contact lens (-7.50). Somehow the results are underpowered, as my eyesight is not as accurate as with the right eye and I perhaps may need one extra quarter. With the right eye (-7.25, -1.00, 140º) I would say that it matches more accurately to my current contact lens (-6.50, -0.75, 140º), though I’m actually thinking about reducing it a quarter as there is one eye (this one) that sees better than the other. Does this work for you? (I need to compare my results with others). I guess that the astigmatism must be taken in consideration for this formulas, though I don’t know how to apply it.

Here is a cool site which explains how to do it, but is nothing I can transform into an excel formula (or don’t know how could I do it).

About nº3: How to convert from Contact Lens to Glass

I know, this seems to be a bit odd as probably no one would do this. It’s just either “because I can” or as another proofcheck that upon the known vertex distance (either real or estimate), it will match the numbers. Again, not sure if this can be tied too to the astigmatism for the calculations.

About nº4: How to estimate the probable vertex distance

No clue how to get this working, but I would say that shouldn’t be that hard, …Right? :sweat_smile:

To close the topic, it would be cool to have any kind of feedback related to any error, something unclear, or any output results that don’t match your prescriptions and cm measurements to find a solution to it.

See yah! (a bit blurred though)


I must say, this is a beautiful spreadsheet

maybe @Markiyan can chime in

Hi again!

A week later since I’ve opened this thread I have finally figured out all four formulas I was looking for, and I can offer you a more or less final version of the template, with a much more cleaner view than the previous draft. Here is the link:

Can you please give me some feedback about it? Was it usefull for you? Did the output of the template match your differentials, contact lens, prescriptions and so on? (Just fill in the cells colored in white, as easy as that).

If there is anything unclear, gladly I help you using it.

PS: Apparently it seems that if I save it to .ods, the resulting file is broken and the formulas do not work. In case you are using OppenOffice I’m not sure if I could help you with it :worried:


This iteration of the excel sheet is a lot more beautiful that’s for sure

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