A Guide to Reading the Numbers on Your Prescription for Eyeglasses

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May 8, 2023 by Marjorie R. Rogers, MA (English), Certified Consultant

Prescription eyeglasses are a crucial tool for those with vision problems, but understanding how to read the numbers on your prescription can be daunting. In this guide, we will provide a comprehensive guide on how to read and interpret the numbers on your prescription eyeglasses.

Sphere (SPH)

The sphere number, also known as SPH, refers to the strength of the lens required to correct nearsightedness or farsightedness. If the number is negative, it indicates nearsightedness, while a positive number indicates farsightedness. The number is measured in diopters (D) and ranges from -20 to +20.

Cylinder (CYL)

The cylinder number, also known as CYL, indicates the degree of astigmatism present in your eyes. Astigmatism is a common vision problem that causes blurred or distorted vision due to the irregular curvature of the cornea or lens of the eye. This can make it challenging to see fine details and can cause discomfort or headaches when left untreated. The cylinder number is also measured in diopters and can range from 0 to +/- 6.00.


The axis number is only present in prescriptions for astigmatism and indicates the orientation of the cylinder lens required to correct your vision. The axis number is measured in degrees, ranging from 0 to 180.


The add number is used to correct presbyopia, a condition that affects people over the age of 40 and causes difficulty in seeing up close. It is the additional strength the lens needs to correct vision for reading or other near activities. The add number is measured in diopters and ranges from +0.75 to +3.00.


The prism number is used to correct double vision or eye alignment problems. It measures the amount of deviation of light passing through the lens, and the number is expressed in prism diopters (PD).

Base Curve

The base curve number indicates the curvature of the back surface of the lens, which must match the curvature of your cornea for optimal vision correction. This number is expressed in millimeters and ranges from 8.00 to 10.00.

Pupillary Distance (PD)

The pupillary distance, or PD, is the distance between the center of your pupils in millimeters. It ensures that the lens is properly aligned with your eyes for optimal vision correction.

Reading and understanding the numbers on your prescription for eyeglasses is essential to ensure that your vision is corrected correctly. By familiarizing yourself with the various terms and numbers used in an eyeglass prescription, you can better communicate with your optometrist or optician and select the best eyeglasses for your needs.

About Author (Marjorie R. Rogers)

The inspiring mum of 6 who dedicates her time to supporting others. While battling with her own demons she continues to be the voice for others unable to speak out. Mental illness almost destroyed her, yet here she is fighting back and teaching you all the things she has learned along the way. Get Started To Read …