If you currently wear glasses and are thinking of switching to contact lenses, you may have assumed that your glasses prescription would simply carry over to your lenses. Unfortunately that’s not the case; the two prescriptions are different because of the distance the lenses sit from your eyes.

While your glasses prescription can serve as a starting point, you will need a contact lens consultation to get the correct contact lens prescription.

What are the differences between a contact lens prescription and glasses prescription?

The optics of the lenses in spectacles and contacts are different. This is because glasses are perched on your nose, at a short distance from your eyes, whereas contact lenses sit on the surface of your eye. Therefore, the two need different prescriptions to give you the best vision correction, and you should not transfer your prescription manually from glasses to contacts. If you wear glasses and are thinking about contact lenses, you will need to see your optician for a contact lens consultation.

Are there different types of contact lenses? Which one is right for me?

There are different types of contact lenses available for different prescriptions. Your optician will choose the correct type of lenses for your prescription to prevent damage to your eyes.

For example, many people who wear glasses are not aware that they have astigmatism, a condition in which the irregular curvature of the eye causes blurred vision. Glasses correct astigmatism with lenses that are held firmly in place by the frame. However, contact lenses can rotate in the eye since they float on a thin film of tears. That’s why people with astigmatism need a special type of contact lenses  called toric lenses to correct this condition. Toric contact lenses are designed for rotational stability to ensure they remain correctly oriented in the eye. An optician will flag this during your consultation and prescribe the correct type of lenses for you.

Why do I need a new eye test for a contact lens prescription?

In addition to the numbers on your glasses prescription, your optician will need to make some additional measurements if you’re planning to wear contact lenses. Your contact lens prescription will contain two numbers called the ‘base curve’ and ‘diameter’ , which determine the fit of the contact lens on your eye. Most disposable contact lenses come in a selection of base curves and diameters, and it’s important to find the one which will best fit your eyes.

If you have astigmatism, you’ll have to wear toric contact lenses and your prescription will include measurements of ‘cylinder power’ and ‘axis’, which are needed to correct this condition.

What are the side effects of using my glasses prescription for contact lenses?

Ordering the wrong type of contact lenses or the wrong prescription can lead to symptoms such as blurry vision , headache, eye fatigue, and eye pain.1 In the worst-case scenario, contact lenses purchased without a proper prescription and eye examination may lead to eye health complications and potentially lasting damage.2

Need more information about different types of contact lenses? Have a look through our Contact lenses page, or read our article explaining what glasses prescriptions mean. You can also book in online for an eye test at Specsavers.


  1. American Academy of Ophthalmology. (no date). Can outdated contact lenses harm your eyes? [Online]. Available at: https://www.aao.org/eye-health/ask-ophthalmologist-q/wearing-outdated-contacts [Accessed 9 November 2019].
  2. Şengör T, Alkibay S, Ermeç Sertoğlu A, Aydın Kurna S. Survey to Determine Perceptions and Practices in Contact Lens Use and Identify Key Features of Safe Use Education. Turk J Ophthalmol. 2018;48(6):288–294. [Online]. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6330667/ [Accessed 9 November 2019].