Understanding Your Eye Prescription: SPH and CYL Explained

When it comes to your eye prescription, understanding the terms spherical (SPH) and cylindrical (CYL) values is crucial. Both these values play significant roles in determining the full extent of your eye power, or refractive error. This article aims to demystify these terms and explain why both are essential for an accurate understanding of your vision correction needs.

What are SPH and CYL?

Spherical (SPH) and cylindrical (CYL) are key components of your eyeglass or contact lens prescription. SPH measures the power in a lens to correct nearsightedness (myopia) or farsightedness (hyperopia).

A negative SPH value indicates nearsightedness. A positive SPH value indicates farsightedness.

Cylindrical (CYL) measures the power in a lens to correct astigmatism. Astigmatism is a refractive error caused by an irregularly shaped cornea or lens, which results in distorted vision.

Why Both SPH and CYL are Important

It might be tempting to combine these values, but doing so can lead to an incorrect understanding of your vision correction needs. For instance, if your prescription reads -1.00DS / -1.00DC x 90, these two components can not be added directly. Instead, each value serves a unique purpose in providing a precise vision correction.

Eye Check is Essential

To truly understand your eye power, you need to undergo a comprehensive eye examination. During this examination, you may find that only SPH is necessary, only CYL is needed, or both SPH and CYL are required depending on your specific refractive error.

Spherical vs Cylindrical Powers

While spherical and cylindrical powers are distinct, they work together to correct different aspects of refractive error. Spherical power corrects myopia or hyperopia, while cylindrical power addresses astigmatism.

Combining SPH and CYL for Total Eye Power

To determine your total eye power, you must consider both spherical and cylindrical values. For example, in the prescription -2.00DS / -1.00 DC x 90:

-2.00DS is the spherical power on your cornea, indicating the primary refractive error. -1.00DC indicates the cylindrical power, designed to correct astigmatism. The axis (90 degrees) tells you the orientation of the astigmatism.

In simple terms, the spherical power gives you the overall correction on your cornea, while the cylindrical power provides a specific correction for astigmatism at a particular axis.

Conclusion

Understanding and correctly reading your eye prescription is crucial for achieving optimal vision correction. Both SPH and CYL are important components of your prescription, and they should not be combined or disregarded. Always consult with your optometrist and specify each parameter accurately when purchasing eyewear. By understanding the role of SPH and CYL in your prescription, you can ensure you receive the best vision correction for your specific needs.

Questions and Answers

Q: How do I read my eye prescription?
A: Your prescription includes SPH and CYL values. SPH measures nearsightedness or farsightedness, while CYL corrects astigmatism. Both are important for accurate vision correction. Q: Can I add SPH and CYL?
A: No, SPH and CYL cannot be added. They are distinct values that address different aspects of your refractive error. Adding them would result in an incorrect prescription. Q: Why is it important to purchase eyewear with the correct SPH and CYL?
A: Proper SPH and CYL ensure clear and comfortable vision. Ignoring either value can lead to distorted or unclear vision, potentially causing eye strain and other discomfort.