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Lens Parameters - Definitions

Here, we describe and define all the different parameters that are involved in the world of contact lenses:

Understanding your prescriptions

Common Abbreviations on Lens Packages and Prescriptions:

PWR = Power
SPH = Sphere (Power)
D = Diopter (Power)
BC = Base Curve
DIA = Diameter
AX = Axis
CYL = Cylinder
ADD = Addition
Vis = Visual Acuity (Visual Sharpness)

Power
This is where you fill in the refractive power you need for your lenses. A minus sign (-) indicates nearsightedness, while a plus sign (+) indicates farsightedness.

Diameter
Diameter represents the size of the lens. For some lenses, there's only one diameter option, and in that case, you may not need to specify it. Otherwise, you can find the diameter on your old lens packaging, often abbreviated as DIA. Alternatively, your optometrist can provide you with this value.

Base Curve
Base curve determines the curvature of the lens. Like diameter, some lens models have only one base curve, so you may not need to specify it. Otherwise, you can find the base curve value on your old lens packaging, often abbreviated as BC.

Cylinder and Axis
For toric lenses that correct astigmatism, you'll need to provide both cylinder and axis values. These are typically found on your old lens packaging, abbreviated as CYL and AXIS, respectively. Sometimes, they are simply listed as values, usually after the sphere power. For example, it might read -4.00 -1.25 x 180, where -4.00 is the sphere power, -1.25 is the cylinder, and 180 is the axis.

Addition (ADD)
For multifocal or progressive lenses, you'll often need to specify the addition (ADD). ADD indicates how progressive the lens is, i.e., how much the power changes from the top to the bottom of the lens. Progressive lenses are commonly used by people with presbyopia, as they help with both near and far vision.

Visual Acuity (Vis)
Visual acuity is often indicated on your prescription from the optometrist. It measures how well you can see with the prescribed lenses or glasses. When ordering contact lenses, you can usually ignore this value, as it's not a parameter you need to consider unless you're curious. A Vis value of 1.0 represents normal vision, values below 1.0 indicate worse-than-normal distance vision, and values above 1.0 indicate better-than-average distance vision.

Colored Lenses
When ordering colored lenses, you'll need to specify the color you want. Keep in mind that the effect on your eye color may vary from person to person.

Other Lens Terminology

Material
This refers to the material the lens is made from. Different manufacturers often have proprietary materials, such as hydrogel or silicone-hydrogel. Hydrogel lenses can hold a lot of water and are comfortable for sensitive eyes, while silicone-hydrogel lenses have high oxygen permeability, allowing for extended wear without eye damage.

UV Protection
Some lenses come with UV protection, while others do not. If you spend a lot of time outdoors without sunglasses, UV protection in your lenses can be beneficial. However, this is not typically a primary consideration when getting contact lenses.

Handling Tint
Some lenses have a slight blue or light green tint to make it easier to see if the lens is inside out or locate it if dropped. Generally, the handling tint does not change how others perceive your eye color when the lens is in place, but there can be exceptions, especially if you have very light eyes to begin with.