Philip Walsh - How do I understand what my glasses prescription means?

Publish Date
Thursday, 3 August 2017, 12:15PM
Photo: Getty Images

Photo: Getty Images

By Philip Walsh

Glasses prescriptions to the untrained eye can appear to be a random sequence of numbers and letters, but once you understand what each number means you can understand how to read this code.

Put simply, the numbers represent diopters, a unit used to describe the amount of correction an eye needs. Generally speaking, the further away from zero these numbers are, the more correction the lens requires.

These numbers are listed under the letters OD and OS. OD stands for oculus dexter, which is the right eye and OS stands for oculus sinister, which means it is for the left eye, while If you see the letters OU, this involves both eyes.

The first numbers in the series will also have positive or negative signs attached to them. A plus sign signals the eye is far-sighted (known as hyperopia), while a minus sign signals the eye is near-sighted (known as myopia). This first number in the sequence is known as the spherical number.

If you have astigmatism, there will be a second and third number. The second number is the cylinder number, which measures the astigmatism and can be positive or negative. The third number, known as the axis, describes the orientation in the eye with a number between 1 and 180.

In the case of no refractive error, you will see a 'pl', which stands for plano.

If you are over 45, there may be a number where it says ‘ADD’. This is your reading addition and relates to the amount of additional correction needed to focus at close distances. If a measurement is shown in this section, it means you have different prescriptions for distance and reading.

Finally, if a PD (pupillary distance) is included in your prescription, this just means the distance between your eyes. This can be an important figure to help your optometrist best fit the lenses correctly.

For additional assistance with understanding your glasses prescription, get in touch with your local Specsavers store or visit, for more information.

About Philip 

Philip is an experienced optometrist with a Bachelor of Optometry from Auckland University. He’s worked in the UK, Zimbabwe and is now the Optometrist Director at the Specsavers New Lynn store in Auckland, one of 52 Specsavers stores across the country. 

Improving access for all Kiwis to high-quality eye care and eyewear is Philip’s passion. What he loves about his role at Specsavers is providing all his patients with excellent customer service and professional eye care with the latest technology and knowledgeable well-trained staff.

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