A year ago I went to an optometrist and got a prescription that looks like this:
Spherical Cylinder Axis Add H. Prism V. Prism
R +1.00 -1.25 093 -- -- --
L +1.00 -1.50 070 -- -- --
I used this prescription to order glasses from Zenni and got great results.
Today I saw an ophthalmologist for a medical issue and she also evaluated my eyes for an updated prescription. She said that it had only changed a very tiny bit from my previous prescription and I might not need to get new glasses. She wrote this:
Spherical Cylinder Axis Add Prism
OD -0.50 +1.50 5 2.50 <blank>
OS -0.75 +1.75 155 2.50 <blank>
She did mention that the way that ophthalmologists write prescriptions is different than how optometrists do it, because they are interested in different things. But she didn’t explain the math.
However, I do not know how to submit the second prescription and get the right results. Does the second prescription have values that somehow offset one another once you put it all together, or is it a completely different notation? Will Zenni interpret this as simply a different way to write a prescription and get it right, or am I going to end up with glasses that look like the bottoms of Coke bottles?
I’ve taken ophthalmologist prescriptions to Lenscrafters optometrists, and they know exactly what they’re looking at and how to convert it. I watched them actually do the math, not that I followed it very well.
So I should be able to submit either prescription and get the same glasses back? Kind of like if I give a mathematician a Cartesian plan and say that an angle is 135° and I tell another one the angle is -225° and they both draw the same thing?
I guess, but ISTM there is also a fundamental difference in perspective: are you writing down the [extra] power of your lens, or the corrective lens? That will account for a sign difference. Lenses with positive and negative focal lengths are not the same, whereas 135° = −225°.
I also noticed that one prescription has simply
L and another has
OS (emphasizing the eyes), and neither have
LS, but I do not think the choice of terminology is significant.
I agree. OD/OS is Latin and R/L is English, that’s about it. Never seen LD/LS for eyeglasses but I’ve seen LD for camera lens glass.
Conversion aside, you will need someone to measure your pupillary distance as well, unless Zenni already has it on file.
They have it. The optometrist I saw last year measured it with a machine. I assume that does not normally change.