Lens Parameters - definitions

Here we explain the most common parameters and terms you will encounter when ordering contact lenses. These values are typically found on your lens packaging or on the prescription provided by your optometrist.

Understanding your prescription

🟪 Common abbreviations on lens packages and prescriptions

  • PWR / SPH / D = Power (Diopter strength)
  • BC = Base Curve
  • DIA = Diameter
  • CYL = Cylinder (for astigmatism)
  • AX / AXIS = Axis (for astigmatism)
  • ADD = Addition (for multifocal lenses)
  • VIS = Visual Acuity (visual sharpness)

Power (PWR / SPH / D)

This indicates the refractive power you need in your lenses.

  • A minus (-) value means you are nearsighted (myopia)
  • A plus (+) value means you are farsighted (hyperopia)

Diameter (DIA)

The diameter defines the size of the lens.

Some lenses are only available in one diameter, meaning you don’t need to choose. Otherwise, you will find the DIA value on your old packaging or from your optometrist.

Base Curve (BC)

The base curve describes the curvature of the lens and how it fits your eye.

Like diameter, some lenses come in a single BC. If not, you can find this value on your previous packaging or prescription.

Cylinder (CYL) and Axis (AX)

These values are required for toric lenses that correct astigmatism.

They are often written together with the power. For example:

–4.00 –1.25 × 180

  • –4.00 = Sphere (Power)
  • –1.25 = Cylinder
  • 180 = Axis

Addition (ADD)

ADD is used for multifocal or progressive lenses.

It shows how much the power increases for near vision and is typically used by people with presbyopia who need help seeing both near and far.

Visual Acuity (VIS)

Visual acuity measures how well you see with your prescription.

You usually do not need this value when ordering lenses online.

  • 1.0 = Normal vision
  • Below 1.0 = Reduced distance vision
  • Above 1.0 = Better than average distance vision

Colored lenses

When ordering colored contact lenses, you select the color you want. The final effect may vary depending on your natural eye color.

Other lens terminology

🟪 Material
Lenses are typically made from hydrogel or silicone hydrogel materials.

  • Hydrogel = High water content, comfortable for sensitive eyes
  • Silicone hydrogel = Very high oxygen permeability, ideal for longer wear

🟪 UV protection
Some lenses include UV protection. This can be beneficial if you spend a lot of time outdoors, but it should not replace sunglasses.

🟪 Handling tint
A light blue or green tint added to make the lens easier to handle. It does not affect how your eye color looks when wearing the lens (with rare exceptions for very light eyes).