What are BC and DIA values?
What are BC and DIA values?
For your contact lenses to fit perfectly and give you clear vision, the base curve and the diameter matter just as much as the dioptre strength (D or PWR). Here we explain briefly and clearly what is important.
BC – Base curve
The base curve, usually stated in millimetres, determines how well the contact lens adapts to the curvature of your eye. It is also described as flat, medium or steep and is normally between 8 and 10 millimetres.
DIA – Diameter
The diameter should match the size of your eyes perfectly to ensure clear vision. Soft contact lenses usually have a diameter of 13 to 15 millimetres, whereas hard lenses measure only 9 to 10 millimetres.
PWR / SPH – Power
This value helps correct short-sightedness (minus sign) or long-sightedness (plus sign). The sign is followed by a number indicating the vision correction required – starting at 0, in steps of 0.25 dioptres.
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