How to understand your contact lens prescriptions - Important parameters!
Anyone who wants to buy contact lenses should know the necessary parameters. The contact lens parameters can be found in the prescription written by an eye doctor (or optometrist or ophthalmologist). It is important to note that contact lens prescriptions and eyeglass prescriptions are not the same.
Please also note that the data obtained by the Optician or Ophthalmologist should not be older than one year, as the parameters of the eyes change with age.
- The contact lens parameters you need to know
- How to determine a contact lens prescription?
- The difference between a contact lens and spectacle prescription
- Additional information on a contact lens package
- Not every contact lens brand suit each patient's needs
The contact lens parameters you need to know
Curvature (BC)The base curve of a contact lens describes the curvature of the lens in millimeters, to provide the highest comfort while wearing lenses, i.e. how well the lens attaches to your eye. Normally these parameters are between 8–10 mm.
Dioptres / Sphere (D/dpt./S/SPH/PWR)Sphere is the power of the contact lens. The unit of measure for sphere power is a diopter, or D. In general the spherical power of a lens is indicated with a plus sign (+) for hyperopia and a minus sign (-) for myopia.
Average (DIA)This value is the diameter (or size) of the lens. Soft contact lenses have a larger diameter from 13.00 to 15.00 mm than hard contact lenses from 9 to 10 mm.
Cylinder (CYL)The cylinder value is needed for the manufacture of contact lenses for astigmatism. It is a negative value, which makes any correction for the curvature of the cornea.
Axis (A/ACH/AXIS/AX)The axis is required for astigmatism as a supplement to the contact lens with cylinder. It describes the exact position of the curvature on the cornea and is given in a range of 0° – 180°. Please note that a degree of zero is also written as 180. The number 90 means the vertical position of the eye, and the number 180 corresponds to the horizontal meridian.
Addition (ADD)ADD is the difference between the dioptric value of the far vision and the dioptric value of the near vision. Values up to 1.25 are regarded as low, up to 2.00 as average and up to 3.00 as high.
How to determine a contact lens prescription?
The difference between contact lens and spectacle prescription
So, if you are also wearing “glasses”, be careful not to mix the prescriptions, when you buy new contact lenses. Furthermore, the measurement method between glasses and contact lenses is slightly different, as eyeglasses prescription needs to measure the distance between the eyes.
Additional information on a contact lens package
The oxygen permeability is given with the value “Dk/t”. The longer the lenses remain on the eyes, the more oxygen permeable they should be. If the value is too low, redness, or itching and burning may occur in sensitive eyes.
Not every contact lens brand suit each patient's needs
|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|