What Does PWR/SPH Mean in Contact Lens Strengths – Prescriptions 101

close-up of a contact lens prescription

Updated June 24, 2024A 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.

What is SPH in Contact Lenses?

SPH, short for sphere, in a contact lens prescription refers to the lens power needed to correct your vision. It’s the same as PWR, which you might see on some prescriptions. Measured in diopters (D), SPH helps to correct nearsightedness (with a negative value) or farsightedness (with a positive value). This ensures that light focuses correctly on your retina, giving you clear vision. So, whether your prescription says SPH or PWR, it’s guiding you to the right lens strength for your eyes.

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.

Why PWR Matters

A precise PWR is vital: too weak, and your vision remains blurry; too strong, and you could experience strain and discomfort. An incorrect PWR can lead to suboptimal vision and eye strain, potentially causing headaches, fatigue, and even worsening eye health over time. Accurate PWR ensures that the lenses help rather than hinder your vision, providing comfort and preventing long-term complications.

Knowing how PWR levels in contact lenses affect your daily life is key for clear vision and eye health. Getting the power just right can make everything, from driving to using your phone, easier and more comfortable. It’s important to match your lenses to what you do every day.

Optometrists play a big role in this by adjusting the lens power to meet your specific needs, helping you avoid eye strain and discomfort. Regular check-ups and talks with eye care experts ensure your lenses help you see well and live comfortably, supporting all your activities.

The ‘PWR’ in your contact lens prescription is a cornerstone of clear vision. Recognizing its importance is essential for anyone who wishes to achieve the best possible visual outcome. Always ensure that your prescription is up-to-date, and consult with your eye care professional to understand how your PWR supports your lifestyle and vision needs.

Conclusion

Decoding a contact lens prescription might initially appear complex, given its combination of abbreviations, numbers, and terms. However, once you understand the significance behind terms like “PWR” or “SPH” and their corresponding measurements, it becomes a transparent process. Knowing the distinction in designs, from spherical to toric lenses, empowers you to make informed choices about your eye care.

Furthermore, recognizing the fundamental difference between eyeglass and contact lens power ensures you achieve the clearest vision possible. While this guide provides a comprehensive overview, any specific queries or concerns regarding your eye health and prescription should be directed to your trusted Eye Care Professional (ECP).