Cracking the Code: Interpreting Your Prescription


Photo by Mohamed Hassan

Understanding your eyeglass prescription is the key to ensuring you get the right lenses for your vision needs. In this guide, we’ll break down the elements of your prescription, making it easier for you to navigate and order your glasses with confidence.

Sphere (SPH)

The Sphere (SPH) value in your eyewear prescription indicates the lens power required to correct either nearsightedness (myopia) or farsightedness (hyperopia). If your SPH value is negative, it signifies that you’re nearsighted, meaning you have difficulty seeing objects in the distance. Conversely, a positive SPH value suggests farsightedness, which implies challenges with close-up vision. The higher the numerical value of your sphere power, the stronger the corrective lens required to address your refractive error. If you see the word “plano” or “pl” here on your prescription, it indicates that there is no refractive power in the lens for this measurement.

Cylinder (CYL) and Axis:

Cylinder (CYL) and Axis measurements come into play when correcting astigmatism, a condition where the cornea or lens has an irregular shape, leading to blurred or distorted vision. The CYL value indicates the amount of astigmatism present, with higher numbers indicating a more pronounced irregularity. Meanwhile, the Axis value specifies the orientation of the astigmatism, measured in degrees from 0 to 180. If you see the word “DS” or “SPH” here on your prescription, it means there is no astigmatism correction present.

Add Power

Add power, typically found in multifocal prescriptions, denotes the additional magnifying power required for close-up vision. As we age, our eyes often struggle with focusing on nearby objects due to presbyopia, a natural aging process. The add power compensates for this loss of near vision by providing additional magnification in the lower portion of the lens. By incorporating Add Power into your prescription, your eyewear can effectively address both distance and near vision needs, enhancing your overall visual acuity.


The prism measurement in an eyewear prescription is less common but significant for individuals experiencing eye alignment issues, such as double vision (diplopia) or eye strain. This type of correction adjusts the positioning of light entering the eye, helping to align images properly on the retina. It’s expressed in prism diopters (Δ) and may be accompanied by a base direction (up, down, in, or out), indicating the direction of correction needed.

Pupillary Distance (PD)

Your pupillary distance (PD) is the measurement between the centers of your pupils, crucial for ensuring that your eyewear lenses align correctly with your eyes. This measurement is essential for crafting glasses that provide optimal visual clarity and comfort. While some prescriptions may include a single PD value, others may specify a distance for each eye (e.g., right PD and left PD). An accurate PD measurement ensures that your lenses are centered correctly in front of your eyes, maximizing the effectiveness of your corrective eyewear.


Photo by Karolina Kaboompics

While understanding your prescription is important, it’s essential to consult with your eye care professional for a comprehensive assessment of your vision needs. They can explain your prescription in detail and address any questions or concerns you may have about your glasses.

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Ivan Yong

Dr. Ivan Yong is an optometrist with over 12 years of experience in the optical industry. He earned his doctorate from the Southern California College of Optometry and has practiced in multiple settings, including private practice, community health, and ophthalmology. Dr. Yong aims to expand access to affordable eyewear and improve eye health worldwide.