Understanding your prescriptions
A contact lens prescription can contain abbreviations like PWR, BC, DIA, CYL, AXIS and ADD. Understanding these contact lens parameters helps you check your lenses. Ensure they match the model and prescription fitted for your eyes.
Contact lenses are not selected by power alone. Fit, material, diameter, base curve and optical design can vary. When reordering contact lenses, use the model recommended by your eye care professional.
Common Contact Lens Prescription Abbreviations
- PWR = Power
- SPH = Sphere or spherical power
- D = Dioptre, the unit used to measure lens power
- BC = Base Curve
- DIA = Diameter
- CYL = Cylinder
- AX / AXIS = Axis
- ADD = Addition or near addition
- VA / Vis = Visual Acuity
You may see separate values for the right and left eye. These may be labelled R and L. Some prescriptions use OD for right and OS for left.
What Does PWR or SPH Mean on Contact Lenses?
PWR, or power, describes the optical strength of the contact lens and is measured in dioptres (D). SPH, short for sphere, is another term commonly used for spherical power.
A minus value, such as -3.00, is generally used to correct myopia or nearsightedness. A plus value, such as +2.00, is used for hyperopia or farsightedness. A value of 0.00 may also be described as plano and means that no spherical correction is present.
Do not assume glasses power is the same as contact lens power. Lenses sit directly on the eye. Spectacle lenses sit some distance in front of it. Contact lens prescriptions also include specific lens information.
What Does BC Mean on Contact Lenses?
BC stands for base curve and describes the curvature of the back surface of the contact lens. It is normally expressed in millimetres, for example BC 8.4 or BC 8.6.
Base curve is one of several factors that influence how a contact lens fits and moves on the eye. Some lens models are manufactured in only one base curve, while others are available in more than one. If your lens has only one option, you may not need to select BC when ordering.
What Does DIA Mean on Contact Lenses?
DIA stands for diameter and describes the overall width of the contact lens in millimetres. A soft lens might, for example, have a diameter of 14.0 or 14.2 mm.
As with base curve, many products have a fixed diameter. DIA is still an important part of the specification even when there is no choice to make when ordering.
What Do CYL and AXIS Mean?
CYL and AXIS are used with toric contact lenses to correct astigmatism.
CYL, or cylinder, indicates the amount of astigmatism correction. AXIS indicates the orientation of that correction and is measured in degrees.
A toric prescription might look like this:
SPH -4.00 / CYL -1.25 / AXIS 180
In this example, -4.00 is spherical power, -1.25 is cylinder and 180 is axis. Cylinder and axis values vary between models. Do not consider similar-looking toric lenses interchangeable.
What Does ADD Mean on Contact Lenses?
ADD stands for addition or near addition. It is used in multifocal contact lenses. These lenses correct presbyopia, the age-related loss of near focus.
The ADD is the additional near-vision power needed. It is used alongside distance correction. It may be a number or categories like LOW, MID or HIGH.
Multifocal lenses use different optical designs. An ADD value from one model should not be transferred to another product.
What Does Vis or VA Mean?
Vis or VA refers to visual acuity – a measurement of how clearly you can see during an eye examination. It is a test result rather than a contact lens parameter that you normally select when ordering lenses.
Visual acuity can be recorded using Snellen, decimal and logMAR. In decimal, 1.0 is approximately 6/6 or 20/20 vision. Interpret the number in context of your exam, not as lens power.
Do BC and DIA Mean You Can Switch Contact Lens Brands?
No. Two contact lenses with the same power, base curve and diameter are not necessarily equivalent. Contact lenses can differ in material, thickness, surface properties, edge design and optical design.
Reorder the exact lens model fitted for your eyes. Do not choose another product just because PWR, BC and DIA match.
Other Terms You May See on Contact Lens Packaging
Lens Material
Soft contact lenses use hydrogel or silicone hydrogel materials. Silicone hydrogel generally allows more oxygen to pass through. Material alone does not determine comfort or overnight wear.
UV Protection
Some contact lenses include a UV filter. These protect parts of the eye covered by the lens. They do not cover the entire eye or skin. They are not a replacement for sunglasses.
Handling or Visibility Tint
Many clear contact lenses have a very light blue or green visibility tint. This makes the lens easier to see in the blister pack, on your finger or if it is dropped.
A handling tint is not a cosmetic colored lens. It normally does not change your eye color. Do not confuse it with an inside-out indicator. Some lenses have separate orientation markings.
Contact Lens Prescription: What to Remember
PWR, BC, DIA, CYL, AXIS and ADD describe your prescription. Not every value applies to every lens type. Spherical lenses may only require power. Toric and multifocal lenses include more parameters.
Check the product name and parameters against your prescription or packaging. Consult your optician if you are unsure about a value. Do not select replacements based only on similar numbers.
Explore our daily contact lenses for a fresh pair every day. Compare the available models and prescription ranges.