Re Order
Re-order
If you’ve visited your optician for a contact lens fitting and are hoping to buy contact lenses online, the figures and abbreviations on your contact lens prescription might look confusing.
Here’s a quick and easy guide on how to read your contact lens prescription, to ensure you purchase the correct-fitting contact lenses for you.
How to Read Your Contact Lens Prescription
Prescription Layout
When you receive your contact lens prescription on paper, it will be laid out in a table format. If you require different prescriptions in each eye, the rows labelled L (Left) and R (Right) will indicate which eye is which.
Base Curve (BC)
Base Curve (displayed BC on your prescription) signifies the curvature of the contact lens that matches the natural curvature of your eye. This is usually written in millimetres, sometimes appearing as “flat,” “median” or “steep.”
Diameter (DIA)
The diameter (DIA) of the lens indicates the width from edge to edge. Wearing the correct base curve and diameter contact lenses ensures your eye contacts will fit comfortably, whilst reducing the risk of eye strain and other damage.
Power (PWR / SPH / D)
The strength of your contact lens prescription is indicated by the symbols PWR (Power), SPH (Sphere) or D (Dioptres — the unit used for measuring refractive power). The numbers following these abbreviations tell you the strength of your prescription.
Contact lens powers start at 0 (no vision correction needed) and ascend or descend by measures of 0.25 dioptres. A positive number e.g. “PWR +1.75” indicates hyperopia (long-sightedness), whilst a negative number e.g. “D -1.25” indicates myopia (short-sightedness).
The further your PWR number moves away from 0, the stronger prescription is required.
Reading Contact Lens Prescriptions for Astigmatism
If you have astigmatism and are buying toric contact lenses, your prescription will also include the cylinder and axis of your eye.
Cylinder (CYL)The CYL number on your prescription determines the extra power needed to correct astigmatism. It is always a minus number and, just like PWR, moves in increments of -0.25 dioptres.
AxisThe axis indicates the angle of correction needed to correct astigmatism; a condition where irregular eye curvature causes blurred vision. This will be a number between 0 and 180 degrees.
Reading Contact Lens Prescriptions for Presbyopia
Similarly to astigmatism, prescriptions for presbyopia and multifocal contact lenses also include some extra information.
Addition (ADD)The addition figure on your multifocal contact lens prescription signifies the magnifying power added to the lenses which allows clear, up-close vision. This can either be a number between +0.50 and +3.00, or appear as “High,” “Medium” or “Low” power.
Contact Lens Prescriptions vs. Glasses Prescriptions
Contact lens prescriptions differ greatly from your usual glasses prescriptions. If you’re new to contact lenses, or thinking of switching from glasses, it’s vital that you consult your optician for a contact lens fitting to ensure maximum clarity and comfort.
The difference in prescription is caused by distance. Spectacle lenses sit a short distance away from your eyes, while contacts lenses sit directly upon them, altering the PWR prescription of your lenses. A contact lens check at the opticians will also help you determine the correct base curve and diameter required, which you cannot achieve at home.