I recently called my Optometrist to get my eye score so that I could buy my own glasses from the chemist. I was expecting to get a "+2" or "+1" or something like that but instead they gave me something complicated for each eye starting with "175/". I should have written it down but even if I did, someone would still need to help me interpret it.

How does this system work?


I managed to get hold of a new prescription. The form is detailed as follows:

Right lens Sph -0,50 Cyl -0,50 axis 10

Left Lens Sph -0,50 Cyl -0,50 axis 170

Type CR39 SN ARC

  • I think it mentions the axis- 175 degree and not the power(like "+2"). This information seems incomplete. Sep 8, 2016 at 16:13

1 Answer 1


The information you provided

Right lens Sph -0,50 Cyl -0,50 axis 10
Left Lens Sph -0,50 Cyl -0,50 axis 170
Type CR39 SN ARC

is a little bit clearer than you can sometimes see.

When you look at your prescription for eyeglasses, you can sometimes see numbers listed under the prefixes of OS and OD, or OU. They are Latin abbreviations:

You have given 3 numbers (SPH, CYL and Axis) which I will explain below. There are other numbers which may be provided, which I will also go into.

The first number: Sphere (SPH)

The further away from zero the number on your prescription is, the worse your eyesight is and therefore the more vision correction (stronger prescription) you need.

A “plus” (+)  sign in front of the number means you are farsighted (hyperopia), and you find it difficult to see things close to you without correction with spectacles or contact lenses.

A “minus” (-) sign means you are nearsighted (myopia), and you find it difficult to see things far away without correction with spectacles or contact lenses.

These numbers represent diopters, the unit used to measure the correction, or focusing power, of the lens your eye requires, and diopter is often abbreviated "D."

The second number: Cylinder (CYL)

This refers to the "cylinder" or astigmatism, and can be a negative or a positive number. It measures in diopters the degree of astigmatism that you have. The bigger this number, the more astigmatism you have. Astigmatism is caused by an irregularly shaped cornea, causing visual distortion. The irregular cornea shape can be described as more like an American football than a basketball.

The third number: Axis

It is not enough to specify how much astigmatism there is; you have to know where the difference in curvature is taking place. The Axis is a number anywhere between 0 and 180 degrees, which reveals the orientation of the astigmatism and lets the lab know how to position your lenses.

A fourth number: Prism

This usually means that your eyes do not work well as a pair. Prism lenses help prevent double vision or headaches.

A fifth number: Base

This simply tells the lab where to put the prism.

A sixth number: Reading Addition (ADD)

This is for varifocal or bifocal lenses and relates to the additional correction in + needed to correct Presbyopia in order to focus at close distances.

A second number: Pupil Distance (PD)

Also known as Interpupillary Distance and if separate numbers are used, they refer to the distance between each pupil and the centre of the bridge of the nose. If one number is given, it is the distance between each pupil.

The information under Type

The first part: CR39, Poly, NXT...

This refers to lens material suggested and dies not have any bearing on your prescription per se.

CR39 is a type of polymer lens, not to be confused with type POLY which is polycarbonate.

For more information on different lens materials used you can go to this webpage from EyeKit who I am not affiliated to. They are sellers of prescription glasses for sport, leisure and specialist uses, and I do not vouch for the quality of their products.

The second and third parts: SN and ARC

I have not yet been able to determine what these refer to, but again, these do not have any bearing on your prescription per se.

Sources linked

National Eye Institute - Hyperopia

National Eye Institute - Myopia

Specsavers - Your prescription explained

TermWiki - oculus uterque (OU)

WebMD - Presbyopia

WebMD - How to Read Your Eyeglass Prescription

WebMD - What Is Astigmatism?

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