How do you read your contact lens prescription?
The three main measurements on your contact lenses are power, base curve and diameter. Some people’s prescriptions will also include a cylinder, axis, add and in some cases, colour.
When you go for an eye test your optician is legally obliged to give you a prescription and you are free to buy your contact lenses anywhere you like. Buying them online is cheaper and ensures you receive the best deal on your contact lenses. We do not require you to send us your contact lens prescription before you order, but you make sure your contact lens prescription is up to date before making a purchase. You should aim to have an eye exam at least once every two years or more frequently if advised to do so by your optician.
Please also be aware that your contact lens prescription and your glasses prescription are not the same. You require different tests for contact lenses and prescription glasses. You cannot convert one to the other.
What does ‘power’ on a contact lens prescription mean?
The power of your lens in measured in dioptres and this indicates the level of correction your lens must provide to correct and sharpen your vision. The correct power should normally give you 20/20 vision.
If your prescription shows a minus sign (-) this means that you are short-sighted and have myopia.
If your prescription shows a plus sign (+) this means that you are long-sighted and have hyperopia.
What does ‘cylinder’ on a contact lens prescription mean?
You will see a cylinder value on your prescription if you have been prescribed toric lenses to correct astigmatism. It is usually written in minus (-) form.
What does ‘axis’ on a contact lens prescription mean?
You will only have an axis on your prescription if you have astigmatism. The axis is measured in degrees. The axis is needed to compensate for the cornea’s non-spherical shape. The axis will indicate the orientation of the cylinder power and where it should sit.
What does base curve on a contact lens prescription mean?
The base curve is measured to ensure the correct fit of a contact lens on the eye. It should relate to the curvature of your cornea and is measured in millimetres. A lower number indicates a steeper corneal curve.
What does ‘diameter’ on a contact lens prescription mean?
The diameter measures the width of your contact lenses from one edge to another and is measured in millimetres. Wearing a lens with the wrong diameter may result in irritation.
What does ‘add’ on a contact lens prescription mean?
The add power is usually written in dioptres and written as a plus (+) power. It indicates the magnifying power in multifocal (other names include, bifocal or varifocal) contact lenses.
Contact lenses and colour
If you have opted for colour contacts, you will also see the name of the colour on your lens package. Be aware, that depending on your own eye colour and the pigmentation of the lens, the appearance of coloured lenses will differ from person to person.
Contact lens expiry date
Additionally, you will also see an expiration date, make sure that your lenses are in date before wearing them. Out of date lenses may cause irritation when worn.