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How to read the parameters on your contact lens prescription

Anna Sucha

Medically reviewed by Anna Sucha, Optometrist, on 25 May 2021
Written by Leonie Bauer

Anyone who wants to buy contact lenses should know the parameters. These contact lens parameters can be found in the prescription that your eye doctor (or optometrist) gave you after your eye test.

Please note that the data obtained by your eye care practitioner should not be older than one year, as the parameters of the eyes ccan hange with age. Also, it is important to know that contact lens prescriptions and eyeglass prescriptions are not the same.

Contact lens parameters you need to know

Curvature (BC)

The base curve of a contact lens describes the curvature of the lens in millimetres. It ensures that the lens sits well on the eye. Usually, these parameters are between 8-10 mm.


Dioptres / Sphere (D/dpt./S/SPH/PWR)

Sphere refers to the refractive power of the contact lens. The unit of measurement for spherical power is a diopter or D. Generally, the spherical power of a lens is indicated with a plus sign (+) for hyperopia and a minus sign (-) for myopia.


Average (DIA)

Average describes the diameter (or size) of the lens. Soft contact lenses have a larger diameter (13.00 to 15.00 mm) than hard contact lenses (9.00 to 10.00 mm).


Cylinder (CYL)

The cylinder value is required for the production of contact lenses for astigmatism. It is a negative value that corrects the corneal curvature.


Axis (A/ACH/AXIS/AX)

Axis is needed in astigmatism as a supplement to the cylinder. It describes the exact position of the curvature on the cornea and is given in a range of 0° - 180°. Please note that 0° can also be written as 180°. The number 90 stands for the vertical position of the eye, the number 180 for the horizontal meridian.


Addition (ADD)

ADD is the difference between the dioptric value for distance vision and the dioptric value for near vision. Values up to 1.25 are considered low, up to 2.00 are considered average and up to 3.00 are considered high.


How to read your contact lens prescription 

The contact lens values are determined by your optician or ophthalmologist using various tests and measuring methods. Only thanks to an accurate prescription can you buy the right lenses. Please note that all parameters are checked for accuracy every 6–12 months. Vision and eyesight can change throughout life, so fitting is important. If you feel that your vision has changed, you should have your contact lens values checked immediately.

What is the difference between contact lens prescriptions and spectacle prescriptions?

The contact lens prescription and the spectacle prescription differ from each other in a way that spectacle lenses are worn about 12 millimetres in front of the eyes, while contact lenses are placed directly on the surface of the eye. However, if you have a visual impairment, it is necessary to determine both prescriptions so that perfect vision is possible.

So if you want to wear glasses from time to time, be careful not to mix up the prescriptions. Also, the method of measurement for glasses and contact lenses differs slightly, as the distance between the eyes must be measured for the glasses prescription.

What additional information is on the contact lens packaging?

In addition to your eyes' essential values, you will find the water content on the package of your contact lenses, as well as the oxygen permeability.

The drier your eyes are, the lower the water content of the contact lens should be. Contact lenses with a high water content have the unfavourable property of evaporating water when worn for a long time, thus removing moisture from the eye. So you should pay attention to the right material: Hydrogel contact lenses have a high water content, which evaporates quickly and thus draws a lot of moisture out of the tear film. The result: the eye dries out more quickly. If you have dry eyes, you should therefore opt for silicone hydrogel lenses, as these offer good oxygen permeability and thus require 20% less water.

The oxygen permeability is indicated by „Dk/t“. The longer you want to wear your lenses, the more oxygen permeable they should be. If the value is too low, sensitive eyes may experience redness, itching and burning.

Not every brand of contact lenses suits your needs 

Just like shoes and clothes, the measurements and composition of contact lenses can vary depending on the manufacturer. Therefore, you may need to readjust your parameters if you change brands. We strongly recommend that you consult your eye care practitioner when you do so.

Summary

Contact lens Parameters Unit of measurement Abbreviation More information
Dioptres dioptre PWR, D, SPH, dpt from –30.00 to +30.00
Curvature millimeter BC from 8.00 to10.00
Average millimeter DIA from 13.00 to 15.00
Cylinder dioptre CYL, ZYL from –0.25 to –10.00, toric contact lenses
Cylinder axis degree A, AX, AXIS from 0 to 180, toric contact lenses
Addition dioptre ADD from 1.00 to 3.00, multifocal lenses

 

 

 

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Comments

  • Ron

    Hi

    If the vertical lines is blurry when you look at letters or numbers, what axis should the lens have?

    B

    Reply
  • Brown

    Hello, you are awesome! keep going!

    Reply
    • Gergana-Ekaterina
      Lentiamo.co.uk

      Hello,


      Thank you for your kind words.


      Have a lovely day!


      Reply

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