I believe that there must be a formula that encompasses both the spherical and cylindrical diopters per eye, then averages the two numbers (or keep them separate), eg. OD: [sph diopters + (cyl opters)/2] opters VA equiv (total on chart)
OS: [sph diopters + (cyl diopters/2] opters VA equiv (total on chart)
Lets say we have OD: -1.75 -2.00 x 150°
And. SD: -1.75 -1.50 x 040°
Would be OD: -3.75 --> 20/500 OAV
SD: -2.50 --> 20/250 SAV
= Avg of 20/375 combined
If one ignores a strong astigmatism, the Visual Acuity is likely too generous!
I need to convert my scrip (the example) for my driver's license app. Using a chart I combined my astigmatism diopters/2 and added them, since the direction of astigmatism is additive like the +2.00 is additive to the close Rx which is astigmatic with a slight + x mild to mod - and I have progressives, so the additivity goes gradually from +0.00 for distance to +2.00 for close up, i.e. reading, hence my Rxs at the bottoms are:OD: +0.25 -2.00 x 150° and
SD: +0.25 -150 x 40°
The numbers are all additive. Do I have rationale?