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How to read your contact lens prescription

A contact lens prescription includes detailed information specific to your eyes to tell a lens supplier/optician what lenses best fit your eyes and what level of correction is needed to provide the best vision.

Understanding your contact lens prescription is important when purchasing your contact lenses from another source, such as an online retailer or a different optician to the one that supplied you your prescription.

Please be aware that your contact lens prescription is different to your glasses prescription.


How do I understand my prescription?


Most contact lens prescriptions in the UK will be displayed like the one below, or similar, not all specification will necessarily be filled in depending on what visual problem your lenses correct.


  Base Curve Diameter Power/Sphere Cylinder Axis Addition Dominant
Left 8.6 14.2 -4.25 -1.75 100 +1.0 D
Right 8.6 14.2 -4.25 -1.75 100 +1.0 N


Further information on your contact lens prescription will include:

Contact Lens Brand/Name: The name of the lenses you wear, whether they are branded e.g. Acuvue or Focus Dailies or optician's own e.g. Specsavers or Boots.

Expiration Date: This is the date in which your lens prescriptions expire and you should see your optician again to renew your prescription.



What do the categories mean?


Power/Sphere (PWR/SPH): The power of your lens specifies the level of visual correction you need to see perfectly, the further the number is away from the zero the higher your prescription. A minus sign indicates that you are short-sighted and need lenses to correct myopia, and a plus sign shows that you are long-sighted and need correction for Hyperopia.

Base Curve (BC):The base curve is the curvature of the lens in millimetres, and determines how well the lens fits your eye, the lower the number the steeper the curve in your cornea. Some brands use non-numeric base curves such as flat, median or steep.

Diameter (DIA): The diameter is the width of your lens in millimetres, it clarifies how big the lens is and where it will sit on your eye. A lens with the wrong diameter can lead to discomfort and irritation.



Prescriptions for astigmatism include additional figures:

Cylinder (CYL): Is an extra figure needed if you have astigmatism, it defines the level of correction needed for your astigmatism. This figure is always a minus numbers, and increases in a scale of 25 dioptres.

Axis (AX): The axis is the direction needed to correct your astigmatism. This is also a number between 0 and 180 degrees.

Multifocal contact lens prescriptions also include an additional measurement:

Addition (ADD): The addition determines the value of added strength needed to correct your vision when looking at objects close up. This can be either a + number between 0.50 and 3.00, or referred to as high, medium or low.

Dominant: Usually displayed as a D or N to signify which eye is your Dominant eye "D" and which is the non-dominant eye "N" for multifocal/bifocal lenses.



How long is my contact lens prescription valid for?


There should be an expiry date listed on the written prescription given to you by your optician. The average length of contact lens prescription is a year, as this is the recommended interval in which patients should have check-ups. However, a contact lens prescription can be shorter or longer in the UK, as it's based on the professional judgement of the optician fitting your lenses, and when they think it's necessary for your eyes to be re-examined.

When your prescription expires, you should see your optician for another check-up. Usually you'll be contacted by your optician to make an appointment, however if you buy your lenses online, you need to be aware of the expiry date and arrange the appointment yourself. Regular check-ups ensure that you're wearing the right lenses to correct your visual impairment and fit your lifestyle.



Why is my contact lens prescription necessary?


In the UK it is illegal to buy lenses without supplying a valid contact lens prescription as it's considered a medical device. Your prescription should have be given to you by your optician at a contact lens fitting, if it was not, you have a legal obligation to own a copy of it, so do not be afraid to ask.



Can I use my prescription to buy online?


Yes, you can buy online from various suppliers, by providing your prescription. This can usually be done in one of two ways, by either supplying the retailer with a scanned copy of your prescription or by getting your optician to verify your prescription is valid. When purchasing online, always ensure that you are buying from a legitimate source. Some good ways to identify if the company is professional is to look at whether the website appears credible, ensure they have a phone number that you can ring to speak to customer service, read previous reviews from customers and secure payment methods.



Buying online without a prescription


You can buy online without a prescription if your lenses are being supplied by a company who is based outside the UK, where the same laws don't apply. Always ensure you're buying from a reputable supplier and that the contact lens prescription you submit is accurate. If your prescription is not being verified it's a good idea to double check it against your paper prescription or the prescription details on your contact lens box (usually found on the side/end of the box) to ensure there are no mistakes. For example, if you choose to order without your prescription being verified from GetLenses.co.uk your order will be processed by our sister company in Europe, GetLenses BV.



Do I need a prescription for coloured contact lenses?


To purchase coloured contact lenses, the process is the same as normal prescription lenses, even if you do not normally wear contact lenses or glasses. Coloured contact lenses can be worn with no prescription or "plano" as it's also known, but you still require a fitting with an optician to obtain a prescription to purchase them inside the UK.




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