In this post we learn how to read an eye prescription and the typical ranges of spherical, cylinder and axis values. Basically, we answer the questions:
- What is the range of spherical values in an eye prescription?
- how bad can astigmatism or cylinder value get?
- what is the range for the axis number in astigmatic prescriptions?
This information would help determine how good or bad your eyesight is. You could also try using our “How bad is my eye prescription calculator” for a quick explanation of your eye prescription.
How to Read Eye Prescription for Glasses and contact lenses
What does spherical value mean in eyeglasses or contacts prescription
In an eye prescription, the spherical value, also known as the “sph” value, indicates the amount of nearsightedness (myopia) or farsightedness (hyperopia) that needs to be corrected. It is measured in diopters (D). Diopters are the unit of measurement used to indicate the refractive power of lenses.
The range for spherical values typically varies based on the individual’s vision needs and can be positive or negative. The common range for spherical values is usually between -20.00 D to +20.00 D. However, prescriptions can go beyond this range in certain cases, depending on the severity of the refractive error.
A negative spherical value (e.g., -2.00 D), it indicates nearsightedness, meaning the person has difficulty seeing distant objects clearly. If the spherical value is positive (e.g., +1.50 D), it indicates farsightedness, meaning the person has difficulty seeing nearby objects clearly.
Always consult with an eye care professional to determine the most accurate and suitable prescription for your individual vision requirements.
How to read an astigmatism eye prescription
In an astigmatic eye prescription, the cylinder value (CYL) indicates the amount of astigmatism correction required. It is also measured in diopters (D) and represents the difference in refractive power between the two principal meridians of the eye.
The range for cylinder values in astigmatic prescriptions typically varies based on the severity of astigmatism and individual needs. The common range for cylinder values is usually between -6.00 D to +6.00 D, though prescriptions can go beyond this range in certain cases.
A negative cylinder value (e.g., -2.50 D) indicates that the astigmatism correction is required for nearsighted astigmatism. If the cylinder value is positive (e.g., +1.75 D), it indicates that the astigmatism correction is needed for farsighted astigmatism.
Did you know you can convert mild astigmatism prescription to regular prescription for contact lenses? Try our conversion calculator.
Astigmatism prescriptions may also include an axis value (AXIS), which indicates the orientation of the cylindrical correction needed. Like spherical values, it is essential to consult with an eye care professional to determine the most accurate and suitable prescription for individual astigmatism correction. Learn about toric lenses.
How are Sph and Cyl numbers measured
In an eye prescription, the increments for spherical (SPH) and cylindrical (CYL) values are typically in increments of 0.25 diopters (D) across the range.
For spherical values (SPH), they might be written as -0.25, -0.50, -0.75, -1.00, and so on for nearsightedness (myopia), and +0.25, +0.50, +0.75, +1.00, and so on for farsightedness (hyperopia).
Cylindrical values (CYL), also follow increments of 0.25 diopters, such as -0.25, -0.50, -0.75, -1.00 for correcting astigmatism.
These increments allow for fine-tuning the prescription to match the patient’s precise visual needs while maintaining the accuracy of the correction. Your eye care professional will determine the appropriate values for your prescription during an eye examination.
what is the range for the axis number in astigmatic prescriptions?
The axis value in an astigmatic eye prescription represents the orientation of the cylindrical correction needed to correct astigmatism. It is measured in degrees from 0 to 180, indicating the direction of the meridian in the eye that has no refractive error.
The range for the axis value in astigmatic prescriptions is from 0 to 180 degrees. The axis value of 0 degrees refers to the horizontal meridian, and 90 degrees refers to the vertical meridian. The axis can take any value in between, representing the varying angles of astigmatism correction required for individual eyes.
For example, an axis value of 45 degrees means that the astigmatism correction is needed along a diagonal meridian at a 45-degree angle. Similarly, an axis value of 180 degrees means that the astigmatism correction is required along the vertical meridian.
As always, it is crucial to consult with an eye care professional to determine the most accurate and suitable prescription, including the correct axis value, for individual astigmatism correction.
Image Credit: Photo by David Travis on Unsplash