When your optometrist first hands you a prescription for new contact lenses, you’ll notice that it’s filled with all kinds of terms and numbers. Trying to make sense of this information may seem daunting at first, but once you have a grasp of the basics, you’ll have a much better understanding of how your contact lenses will be customized to meet your specific needs. Below is a brief overview of some of the terms you should know when reading your prescription.
Terms Related to Contact Lens Fit
Your contact lenses need to be carefully designed so that they fit as comfortably as possible on your eyes. The fit of your contact lenses is described in your prescription by the following terms:
- Base Curve (BC): The base curve refers to the curvature of the back of your contact lens. For many people, the base curve is often around 8.4 to 8.6 millimeters. Without the right base curve, your contact lens would not stay in place.
- Diameter (DIA): The diameter is essentially the width of your contact lens measured from edge to edge. Most soft contact lenses have a diameter somewhere between 13 millimeters and 15 millimeters. However, if you require specialty contact lenses, the diameter can vary quite a bit depending on your needs.
Terms Related to Vision Correction
Of course, prescription contact lenses aren’t just personalized in terms of fit. They also need to be designed to correct your specific vision problems. Below is a closer look at the terms in your prescription that are related to vision correction:
- Sphere (SPH): Sphere is another term for the power of your contact lenses – in other words, how strong they need to be to help you see clearly. The sphere is measured in diopters, and it is written with a negative sign if you’re nearsighted and a positive sign if you’re farsighted. For example, a patient who is somewhat nearsighted may have contacts with a sphere of -3.00.
- Cylinder (CYL): Individuals with astigmatism will find that their contact lens prescription includes a cylinder. This is essentially the lens power required to correct the distortion to your vision caused by an irregularly shaped eye.
- Axis: Axis is another term that’s relevant for patients with astigmatism. It specifies the orientation of where the astigmatism correction should be placed on the lens. Based on your needs, the axis can potentially fall anywhere from 0 to 180 degrees.
By familiarizing yourself with the terms listed above, you can ensure that you truly understand your contact lens prescription and use that information to make the decisions that are best for your ocular health. Remember, you can always speak to your optometrist if there’s anything on your prescription that you want to clarify further.
About the Author
Dr. Jordana Chettiparampil is a therapeutic optometrist in Richmond who currently holds membership with the American Optometric Association, the Texas Optometric Association, and other organizations. She is proud to offer her patients a wide variety of prescription contact lenses to help them correct their vision. If you’re thinking of getting contact lenses, you can schedule an appointment with Dr. Chettiparampil at Richmond Eye Experts by visiting her website, using her online scheduling tool, or calling (832) 685-2020.