Your prescription explained

Understanding your prescription can make it quicker and easier to buy glasses or contact lenses. If your script is up to date you can fill it online and have your glasses and or lenses delivered to your door.

What do all these numbers, terms and acronyms mean?

Your glasses prescription explained

Prescription exampleRight and left eye

The vision correction needed for each eye may be different. Your glasses and/or contact lens prescription will have a column for the right eye and the left and may have any of the following names or acronyms:

Right eye: RE, R or OD
Left eye: LE, L or OS

SPH (Sphere)

A plus (+) sign in front of the number in the sphere column means you are long-sighted and may have trouble seeing things that are close to you. A minus (-) sign means you are short sighted and may have difficulty seeing things in the distance.

The number in this column represents the strength of the lens needed. The higher the number, the stronger the prescription lens required.

CYL (Cylinder)

If there is a number in this column it indicates, you have astigmatism. This usually occurs when your cornea is more of an oval shape rather than a sphere.

The higher the number, the more significant the astigmatism. There may be a plus (+) or minus (-) sign in front of the number.


The axis measures the orientation of astigmatism in degrees (0-180). This measurement shows where the lens should be positioned to correct the astigmatism. The higher the number does not indicate the level of astigmatism, but rather the position.


The Add or Near Add is the additional power, added on to the sphere power, to give the reading prescription for those who need it.


Prism may be prescribed when your eyes aren’t working well as a team. Prism can help correct double vision, eye strain and headaches by re-directing light to the correct part of the retina.

PD (pupillary distance)

The pupillary distance is the measurement (in millimeters) from the center of one pupil to the center of the other. If this isn’t on your prescription you can measure it yourself by following these steps.

  1. Find a ruler that can measure in millimetres
  2. Stand in front of a mirror, close enough to read the measurements.
  3. Rest the ruler on your nose and line up the 0 on the ruler to the outer edge of your left pupil. The outer edge is closest to your ear.
  4. Holding the ruler steady, find the number that aligns with the inner edge of your right pupil. The inner edge is closest to your nose. Your PD should be between 55 and 70 for most adults.
  5. Check the measurement a few times to ensure it is accurate.

Do I need a separate prescription for glasses and contact lenses?

Yes. A separate prescription is required for contact lenses because they sit directly on the eye. A contact lens script can sometimes be written out at the same time as your glasses prescription, however fitting contact lenses usually requires a few visits to ensure the fit is correct, vision is good and they suit a person’s lifestyle needs.

Your contact lens prescription explained

The sphere, cylinder and axis measurements on your contact lens prescription may be different to your glasses prescription. This is because the contact lenses sit directly on the surface of the eye.

BC (Base curve)

The base curve describes the curvature of the contact lens in millimeters but not all contact lens prescriptions include a Base Curve measurement.

DIA (Diameter)

This describes the size across the lens, but as with the Base curve measurement, not all contact lens prescriptions include a Diameter.

Remember to check the expiry date on your spectacle and contact lens prescriptions. It’s a good reminder to book a comprehensive eye exam to ensure your vision and eye health needs are being adequately addressed.

Book a contact lens fitting

If you’re thinking about getting contacts, but are not sure where to start, book in for a contact lens fitting appointment. We’ll give you a comprehensive eye test, and an examination to see if contact lenses are right for you. You can talk to an optometrist about which lenses might best suit your vision needs and lifestyle, and organise to trial some. Book a fitting now.