Your contact lens prescription is made up of different numbers with positive (+) or negative (-) values that define the ‘settings’ of your lenses. These settings, which include power, sphere, and cylinder, are those that your optician has defined as being the most effective for correcting your vision.
For those of us who aren’t opticians, however, understanding what these words and numbers mean can be difficult. Here, we’ve broken down what the terms ‘cylinder’ and ‘power’ mean for your prescription.
How does ‘power’ look on your contact lens prescription?
The figure in front of ‘power/sphere’ (PWR/SPH) or ‘D’ (dioptres — a unit that measures a lens’ refractive power) indicates the strength of your prescription. This describes the amount of vision correction you need. The number goes up from 0 in increments of 0.25, for example: +1.00, +1.25, +2.00, +2.25, etc. The higher the number, the stronger the vision correction you need.
Does this differ for short-sightedness, long-sightedness and presbyopia?
Does astigmatism affect the power on my prescription?
If you have astigmatism (an irregular curvature of the eye that causes blurry vision), there will be some additional figures displayed on the ‘cylinder’ section of your contact lens prescription.
What does ‘cylinder’ mean?
Cylinder (CYL) is always a minus number, such as -1.25, -1.50, -1.75, etc. It is measured in increments of 0.25, in the same way as the power/sphere figure. CYL denotes the extra power you need to correct astigmatism. The higher the number, the more severe your astigmatism. Axis (AX) describes the orientation of your astigmatism and the angle needed to correct it. It ranges between 0 and 180 degrees.
Can I wear contact lenses if I have a high-power prescription?
People with high-power prescriptions can wear contact lenses safely and comfortably, so if you want to get rid of your glasses, this is certainly an option. Advances in contact lens technology have made it possible for people with strong prescriptions to wear them. Standard contact lenses are readily available off-the-shelf in prescriptions up to -12.00D for short-sightedness, +8.00D for long-sightedness, and -2.75D cylindrical power for astigmatism.1 Extended-range contact lenses are available in spherical powers up to -20.00D for short-sightedness and +15.00D for long-sightedness, as well as up to cylinder power -5.75D for astigmatism.1
However, it’s important to know that soft contact lenses with high powers have thicker edges compared to low-power ones.2 For this reason, they are more likely to be discernible in the eye and less comfortable to wear. The thicker material also means that soft hydrogel contact lenses may cause dry eye in people with high-power prescriptions.2
Many people with high-power prescriptions choose rigid gas permeable (RGP or ‘hard’) contact lenses as they are smaller and thinner. RGP lenses take a little longer to adapt to, but they allow more oxygen to pass through to the eyes, making them the healthier option for those with high-power prescriptions.
Want to learn more about your contact lens power chart, or have a question about your contact lens prescription? Book an appointment with one of our friendly Specsavers opticians today or browse our Contact Lenses page.
What should I do if I have the wrong contact lens prescription?
If the power in your contact lenses is not strong enough, you will not be able to see clearly at near and/or far distances, depending on your prescription. You may also experience symptoms such as blurred vision, headaches, and eye strain. If you think you need a new contact lens prescription, see an optician for a contact lens health check.
- Contact Lens Spectrum. (no date). Specialty and Custom Soft Contact Lenses. [Online]. Available at: https://www.clspectrum.com/issues/2016/december-2016/specialty-and-custom-soft-contact-lenses [Accessed 8 November 2019].
- Contact Lens Plus. (no date). High Power Prescriptions. [Online]. Available at: https://www.contactlensesplus.com/education/best_contact_lenses/high_power_prescriptions [Accessed 8 November 2019].