How to Read Your Glasses Prescription: SPH, CYL, Axis & ADD Explained

Prescription Guide

If you have ever looked at your glasses prescription and felt like you were reading a code, you are not alone. Most prescriptions are simple once you understand what each part means.

Your prescription tells an optical professional how to correct your vision. It may include values for short-sightedness, long-sightedness, astigmatism and reading support. Understanding these numbers can help you choose lenses more confidently, especially when buying glasses online.

What does SPH mean?

SPH stands for sphere. This is the main part of your prescription and shows whether you are short-sighted or long-sighted.

  • A minus number, such as -2.00, usually means short-sightedness.
  • A plus number, such as +2.00, usually means long-sightedness.
  • The higher the number, the stronger the prescription.

What does CYL mean?

CYL stands for cylinder and relates to astigmatism. Astigmatism means the eye is not perfectly round, so light focuses unevenly. This can make vision appear blurred, stretched or distorted.

What does Axis mean?

Axis works with the CYL value. It shows the direction of the astigmatism correction and is written as a number between 1 and 180.

What does ADD mean?

ADD is usually found on reading, bifocal or varifocal prescriptions. It shows the extra power needed for close work, such as reading, phone use or detailed near tasks.

Optician’s note: If your prescription includes an ADD, it does not automatically mean you need varifocals. It means you need additional near support. The right lens depends on how you use your eyes day to day.

Does a stronger prescription mean thicker lenses?

Not always. Lens thickness depends on your prescription, frame size, lens material, pupil distance and how the frame sits on your face. If you are concerned about lens thickness, read our guide: Which Lens Thickness Do I Need?

Can you order glasses before sending your prescription?

Yes. At Burghley & Co, you can choose your frame first and send your prescription afterwards. Every prescription order is reviewed before glazing, helping ensure the frame and lens combination is suitable.

Helpful links

Further reading

For independent guidance on eye care, you can also visit Look After Your Eyes by The College of Optometrists.

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Written by Scott Phippen, UK Registered Dispensing Optician and Founder of Burghley & Co.