Hello, I am just starting to study for ABO exam and have been stuck on trying to figure out how to find Rx when powers are given at certain axis. I can find powers from given Rx, but just going backwards, I just can't grasp the concept so if anyone can explain to me I'd really appreciate it.
For example, what is the Rx when -2.00@37 and -3.00@127?
I can go as far as figuring out that the cylinder power would be 1.00, (difference between two powers) but not even sure whether - or +, because from 37 to 127, it'd be -1.00 but from 127 to 37, it'd be +1.00. Which do I use for the Rx??
And then what is the next step?? take the half of that 1.00 and add it to either -2.00 or -3.00 to get the sph equivalent at either axis or is that not necessary? do I just write the -2.00 then the found cylinder power(- 1.00) at 37? and same for -3.00 +1.00 @ 127? Then which Rx do I write for the answer? Do I need to write both?
For example 2, what is the Rx when -1.00@130 and Plano@85?
This is more confusing because it's not 90 degrees apart, I can't even figure out the cylinder power straight. So do I use 30-45-60 rule to figure out the cylinder power at 40 first? (since 40 is 90 away from 130)? Now then, I take +1.00 multiply that by 0.5 since 85 is 45 degrees away from 130, and get +0.5 for new cylinder power at 40, right?
Then the same question as above, do I just write out the new cylinder power and given powers at given degrees as a correct Rx? so would it be -1.00+0.5@130 or am I completely wrong? I'm just so confused.. Please help.
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