# Eyeglass prescriptions from optometrist vs. ophthalmologist **URL:** \ **Category:** Factual Questions\ **Created:** [February 17, 2022, 7:48pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694 "2022-02-17T19:48:25Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [February 17, 2022, 7:48pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694/1 "2022-02-17T19:48:25Z")
A year ago I went to an optometrist and got a prescription that looks like this: ```auto 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: ```auto Spherical Cylinder Axis Add Prism OD -0.50 +1.50 5 2.50 OS -0.75 +1.75 155 2.50 ``` 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? ---
**Author:** ![Briny\_Deep](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/briny_deep/32/17188_2.png) [@Briny\_Deep](https://boards.straightdope.com/u/Briny_Deep)\ **Post date:** [February 17, 2022, 8:06pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694/2 "2022-02-17T20:06:09Z")
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. ---
**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\ **Post date:** [February 17, 2022, 8:55pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694/3 "2022-02-17T20:55:55Z")
Here are examples from a lens supplier: [https://www.eyeglasslensdirect.com/How-to-ready-my-prescription-s/283.htm](https://www.eyeglasslensdirect.com/How-to-ready-my-prescription-s/283.htm) ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [February 17, 2022, 9:43pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694/4 "2022-02-17T21:43:06Z")
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? ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [February 18, 2022, 12:12pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694/5 "2022-02-18T12:12:01Z")
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 `R`/`L` and another has `OD`/`OS` (emphasizing the eyes), and neither have `LD`/`LS`, but I do not think the choice of terminology is significant. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [February 18, 2022, 12:38pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694/6 "2022-02-18T12:38:11Z")
> [@DPRK](#): > > 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. ---
**Author:** ![DavidNRockies](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidnrockies/32/6279_2.png) [@DavidNRockies](https://boards.straightdope.com/u/DavidNRockies)\ **Post date:** [February 18, 2022, 12:47pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694/7 "2022-02-18T12:47:10Z")
> [@](#): > > There are two different conventions for indicating the amount of cylinder: “plus cylinder notation” and “minus cylinder notation”. In the former, the cylinder power is a number of diopters more convergent than the sphere power. That means the spherical power describes the most divergent meridian and the cylindrical component describes the most convergent. In the minus cylinder notation, the cylinder power is a number of diopters more divergent than the sphere component. In this convention, the sphere power describes the most convergent meridian and the cylinder component describes the most divergent. Europe typically follows the plus cylinder convention while in the US the minus cylinder notation is used by optometrists and the plus cylinder notation is used by ophthalmologists. Minus cylinder notation is also more common in Asia, although either style may be encountered there. There is no difference in these forms of notation and it is easy to convert between them:[[1]](https://en.wikipedia.org/wiki/Eyeglass_prescription#cite_note-1) > > - Add the sphere and cylinder numbers together to produce the converted sphere > - Invert the sign of cylinder value > - Add 90° to axis value, and if the new axis value exceeds 180°, subtract 180° from the result > > For example, a lens with a vertical power of −3.75 and a horizontal power of −2.25 could be specified as either −2.25 −1.50 × 180 or −3.75 +1.50 × 090. [**SOURCE**](https://en.wikipedia.org/wiki/Eyeglass_prescription) ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [February 18, 2022, 6:07pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694/8 "2022-02-18T18:07:46Z")
Conversion aside, you will need someone to measure your pupillary distance as well, unless Zenni already has it on file. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [February 18, 2022, 7:45pm UTC](https://boards.straightdope.com/t/eyeglass-prescriptions-from-optometrist-vs-ophthalmologist/959694/9 "2022-02-18T19:45:18Z")
They have it. The optometrist I saw last year measured it with a machine. I assume that does not normally change.