How to read your prescription

You are ready to order your first pair of glasses and finally experience the relief of a clear, effortless vision – but suddenly you realize that you don’t have a clue which strengths to order...

Don’t worry! We’re here to help. Here is an easy, straightforward guide to the kind-of-confusing paper you received from your eye care professional.

Contact lenses or glasses:

Did you know that your contact lens prescription and your eyeglass prescription is not the same thing?

A lot of people use different strengths for their contacts compared to their glasses. There are a lot of reasons for this, with the most common ones being that they are constructed differently, and that contact lenses refract the light right from the surface of your eyes – while the eyeglasses refract the light a couple of centimeters away. Even though you are a contacts-wearer, a lot of people feel the need to use reading glasses on top of the contacts to read clearly.

Continue reading for a clear understanding of your eyeglass prescription.

OD and OS – Right and Left:
To start reading your prescription right, it is important to make sure you are looking at one eye at a time. A lot of people have different strengths on each of their eyes, so you should always read them separately. The right eye is usually marked with ‘R’, ‘RE’ or ‘OD’. The OD and OS are the professional terminologies used by opticians and eye doctors. It’s the abbreviation for Oculus Dexter, Oculus meaning eye and Dexter meaning right. Similarly, OS stands for Oculus Sinister, referring to the left eye prescription. Other terms for the left eye are ‘L’ or Left Eye ‘LE’.

SPH – Sphere:
The SPH is the most standard measurement on the eyeglass prescription. It simply measures the lens power needed to correct your vision problems, with 0,0 meaning that no spherical correction is needed. The SPH is either measured in plus or in minus. If you have plus (+), it explains that you are farsighted, meaning you have trouble seeing things up close. The minus (-) on the other hand, suggests that you are nearsighted and have challenges seeing objects far away. For both plus and minus, the higher the number, the more correction you need. For instance, a person with -0,25 might not have trouble functioning in their everyday lives, while people with -5,00 are dependent on correcting their sight to navigate their environment.

CYL – Cylinder:
The CYL indicates whether you have astigmatism or not. Astigmatism is a common condition referring to an irregular shape of the cornea. While a CYL of -0,25 might not always be corrected, a CYL of -3,00 can decrease your quality of vision drastically. If the CYL space is blank, it means that you have no astigmatism, or that it is too small to be corrected.

The axis also concerns astigmatism. The number is measured in degrees ranging from 1 to 180 and describes the position in which the astigmatism appears.

ADD – Addition:
The ADD is always measured in plus (+) and refers to the amount of extra power you need to see up close. As we age, the near vision decreases, which is the reason most people start wearing reading glasses. It usually starts in our early 40s, starting with additions like +0.25 or +0.50. These numbers will increase with time, leading to +1.00, +1.50, +2.00 and so on. The addition usually stabilizes around +2.00/+2.50 for both eyes and remains constant from that point. This condition/phenomena is often referred to as Presbyopia.

If you didn’t wear contacts or glasses before your 40s-50s, it is likely that you don’t need correction other than the addition. In this case, your required strength for reading glasses is equal to the number on your addition. This might for instance be +1.00 or +2.50.

If you already need correction, the addition should be added to your SPH (considering you do not have astigmatism). Eg. a SPH of +1.00 and an ADD of +2.00 means you will need +3.00 for reading. For the nearsighted (-), it means that if you have a SPH -2.00 and an ADD +2.00 you require no strength for reading. In these cases, you can just take your glasses off when reading. People who need strengths for both distance and near, often use progressive lenses, where their SPH strengths are in the top, and the SPH + ADD is in the bottom of the lens. A lot of people also opt for two pairs of glasses – one for distance and one for near (reading glasses). Keep in mind that it is always a good idea to ask your optician or eye doctor for your required correction if you have advanced measures.

PD – Pupillary Distance:

The PD is short for the pupillary distance, and is the distance between your pupils, measured in millimeters. The PD is often required to make custom made lenses with more advanced measures – like multifocal lenses.


The prism and base sections are fairly uncommon and are for people who experience eye alignment problems. The Prism denotes the correction needed to align the eyes, while the base specifies which direction the prism needs to redirect the light in.