# Prescription for eye glasses, what do the numbers mean? **URL:** \ **Category:** Factual Questions\ **Created:** [February 11, 2003, 2:12am UTC](https://boards.straightdope.com/t/prescription-for-eye-glasses-what-do-the-numbers-mean/154264 "2003-02-11T02:12:44Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Freyr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/freyr/32/5763_2.png) [@Freyr](https://boards.straightdope.com/u/Freyr)\ **Post date:** [February 11, 2003, 2:12am UTC](https://boards.straightdope.com/t/prescription-for-eye-glasses-what-do-the-numbers-mean/154264/1 "2003-02-11T02:12:44Z")
Okay, I just got an eye exam and everythings fine, but I’ve always wondered about the various numbers and the descriptions associated with them. For example, my prescription reads… For the right eye: **SPHERE** : -3.75 **CYLINDER** : -1.50 \*\* AXIS\*\*: 033 **PRISM** _nothing_ **BASE CURVE** _nothing_ For the left eye **SPHERE** : -6.50 **CYLINDER** : -1.00 \*\* AXIS\*\*: 149 **PRISM** _nothing_ **BASE CURVE** _nothing_ Any doctors of optometry out there care to explain this? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 11, 2003, 2:17am UTC](https://boards.straightdope.com/t/prescription-for-eye-glasses-what-do-the-numbers-mean/154264/2 "2003-02-11T02:17:47Z")
[This page](http://www.usaeyes.org/faq/subjects/script.htm) and [this one](http://www.clevelandclinic.org/health/health-info/docs/2600/2699.asp?index=9988), should help sort things out for you. ---
**Author:** ![Yeah](https://avatars.discourse-cdn.com/v4/letter/y/dbc845/32.png) [@Yeah](https://boards.straightdope.com/u/Yeah)\ **Post date:** [February 11, 2003, 2:19am UTC](https://boards.straightdope.com/t/prescription-for-eye-glasses-what-do-the-numbers-mean/154264/3 "2003-02-11T02:19:17Z")
IAMAO but I do wear spectacles and I’ll take a shot: The sphere is the amount of correction you need. It sounds like you are mildlly nearsighted in the right eye but it’s Coke bottle time on the left. The cylinder is the amount of astigmatism correction you need. I think you probably have so little astigmatism that it doesn’t make much difference to you whether it is corrected or not. The axis is the axis of the astigmatism. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [February 11, 2003, 2:23am UTC](https://boards.straightdope.com/t/prescription-for-eye-glasses-what-do-the-numbers-mean/154264/4 "2003-02-11T02:23:27Z")
The values are in diopters. Your left eye is more myopic than the right (more negative prescription needed to correct), but you are somewhat nearsighted in both. The cylindrical curvature is superimposed upon the spherical one, to correct astigmatism; that is, your human lens has a cylindrical component, too. The axis is in degrees, to align the cylinder. (A pure spherical correction would have no axis.) Nothing else unusual about it. If you had had a prism value, it would be to correct walleyes or crosseyes. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [February 11, 2003, 2:44am UTC](https://boards.straightdope.com/t/prescription-for-eye-glasses-what-do-the-numbers-mean/154264/5 "2003-02-11T02:44:59Z")
Just to elaborate a little, and you may know this already if you have obtained the actual glasses, but a negative prescription will result in a lens that is thinner at the center than the edges. A positive value is the opposite (thicker at the center). You didn’t mention the P.D. value (Pupilary Distance), but it should be in millimeters and represents the supposed distance between the centers of your eyes. This number is intended to match the centers of the lenses no matter what frames are used. In glasses as strong as yours, this should be carefully checked when you get them back from the lab. In much weaker prescriptions (perhaps 1.00 diopters or less) it is not critical, but the wrong value can cause severe eyestrain in strong ones. No, IANAO, but I used to work in an optical lab. ---
**Author:** ![Freyr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/freyr/32/5763_2.png) [@Freyr](https://boards.straightdope.com/u/Freyr)\ **Post date:** [February 11, 2003, 5:53am UTC](https://boards.straightdope.com/t/prescription-for-eye-glasses-what-do-the-numbers-mean/154264/6 "2003-02-11T05:53:55Z")
Thanks, everyone! This is great information.