Hi Trung,

I can only till you what *I* do. But you are correct. To get "spherical equivalent" just divide the Astig part by 2, and add it to the sphere part, thus

-5, -2 (astig) 120 degrees, becomes,

-6 Spherical equivalent.

When you get your "spherical equivalent", just check your "home Snellen with it - and determine what line you can read 1/2 the letters correctly on.

If you order a separate "reading" lens, I just subtract 2 or 3 diopters from the above. So that would be -3 to -4 diopters for reading. (Assume reading at 20 to 16 inches).

As always, you must check this yourself.

For now, just order the "distant" lens, and you should be good. For most of us 20/30 to 20/25 is good enough.

Then, when you get them, get a +2.5 diopter an place it over the minus - and find out what your comfortable reading distance is.

Thank you for such a quick response Mr. Brown and also for being so sincere.

I have a few quick questions about how to go about your personal way to correct astigmatic measurement.

For example, I would divide my CYL, which is -2 by 2, then add it to my -7.25 SPH which would make the SPH equivalent to -8.25. Should I then subtract 2.75 from that -8.25 for my new prescription? I just want to have assurance about the new prescriptions I am about to order.

Thank you.

- Trung