A typical contact lens prescription contains many numbers and abbreviations. One of the most important details in a lens prescription is “PWR,” which stands for “power.” This refers to the refractive power that your eye will need to be able to see with 20/20 vision. Simply put, “PWR” refers to the strength of your contact lens.
Some contact lens prescriptions contain “SPH” instead of PWR. This abbreviation stands for “sphere,” and it means the same thing as PWR.
In this article, we discuss everything you need to know about contact lens power.
Contact lens power
The power of a lens is measured in diopters. The higher the diopter, the stronger the vision correction you need. The power of a lens also goes up from zero in increments of 0.25. If the number has a plus sign before it, that means you are farsighted. If it has a minus sign before it, that means you are nearsighted.
For example, if your contact lens prescription reads +2.25 under PWR, that means you need 2.25 diopters of strength to correct farsightedness or hyperopia. Inversely, if your prescription reads -2.25, that means you need 2.25 diopters of strength to correct nearsightedness or myopia.
A contact lens prescription with a negative value under PWR will also include values under “CYL,” which stands for “cylinder,” and “AX,” which stands for “axis.” CYL refers to the extra correction needed for astigmatism—an eye condition that causes blurry vision. It often occurs with either myopia or hyperopia. The value under CYL is always shown with a minus sign.
AX, on the other hand, refers to the direction where another power is added in the contact lens to correct astigmatism. It is measured in degrees.
Contact lens designs and their powers
Not all contact lenses have the same power throughout. For example, toric lenses have different powers in different areas to correct astigmatism. Here’s a quick look at the different contact lens designs and their powers. Note that these include both standard hydrogel and silicone hydrogel lenses.
- Spherical contact lenses – Spherical lenses have the same lens power throughout the entire optical part of the lens. Spherical lens powers are available in 0.25 increments. In higher powers, the increments become 0.50 diopter. This includes powers above +6.00, but this may vary depending on the contact lens brand. For example, you may find spherical lenses in +6.50 diopters but not -6.25 diopters.
- Toric contact lenses – Toric contacts have different powers in different meridians of the lens. As such, they’re able to focus on different parts of the lens to correct vision problems that occur due to astigmatism. Most toric lenses are available in CYL power increments of 0.50 diopter starting from -0.75 diopter, e.g., -0.75, -1.25, -1.75, and -2.25.
- Multifocal contact lenses – Multifocal lenses, including bifocal contacts, have different power zones for near and far vision to correct presbyopia—an age-related eye condition that causes blurry vision. Some multifocal lenses can also correct astigmatism.
- Cosmetic contact lenses – Cosmetic contacts are sold either with no power, referred to as “Plano” or with powers just like spherical lenses. Typically unless they are made-to-order cosmetic lenses are not available to correct astigmatism or presbyopia. Regardless, you’ll still need a prescription from an eye care professional (ECP) to purchase these lenses.
If you have previously worn eyeglasses, it is worth noting that the power of your eyeglasses is different from the power of your contact lenses. That’s because a contact lens sits directly on the surface of your eye, while eyeglasses sit about a centimeter in front of it. As such, eyeglasses must account for that distance with extra power.
Hopefully, after reading this article, you’ll have a much better understanding of lens power and what it means when it comes to correcting refractive errors. If you have any other questions related to your contact lens prescription, consult your ECP.