Reading Your Glasses Prescription: A Plain-Language Guide

What You're Actually Looking At

After an eye exam, your optometrist or ophthalmologist hands you a slip of paper filled with abbreviations, plus and minus signs, and decimal numbers. It can look cryptic — but each value has a precise, predictable meaning. This guide walks through every field so you can read your prescription with confidence.

Your glasses prescription describes how your lenses must bend light to bring images into focus on your retina. If you're unsure why you need correction in the first place, our article on refractive errors explained covers myopia, hyperopia, astigmatism, and presbyopia in plain language.

The Core Abbreviations, Defined

Most prescriptions are organized in two rows — OD (right eye) and OS (left eye) — sometimes followed by a combined OU value. Within each row, you'll typically see these fields:

• SPH (Sphere): The main focusing power of the lens, measured in diopters. A minus sign (−) indicates nearsightedness; a plus sign (+) indicates farsightedness. Values generally range from plano (0.00) to ±20.00, though most prescriptions fall within ±6.00.
• CYL (Cylinder): The power needed to correct astigmatism. If this field is blank or reads "DS" (diopters sphere), you have no significant astigmatism in that eye.
• AXIS: A number from 1 to 180 (degrees) that specifies the orientation of astigmatism correction. It is only meaningful when a CYL value is present.
• ADD: The additional magnifying power added to the bottom of a bifocal or progressive lens, primarily for near vision in people with presbyopia. It is always a positive number, typically between +0.75 and +3.50.
• Prism & Base: Less common. Prism corrects eye alignment problems; the base indicates the direction of the prism. Most prescriptions do not include these fields.

Reading a Sample Prescription

Consider this example:

Translation: both eyes are nearsighted (negative SPH), both have mild astigmatism (negative CYL with an AXIS orientation), and the wearer needs reading help (ADD +2.00), indicating presbyopia. The left eye has slightly more astigmatism than the right.

Once you understand your prescription, you can explore how different correction formats work — glasses, contacts, or surgery — in our overview of vision correction choices.

Glasses vs. Contact Lens Prescriptions

A glasses prescription is not automatically transferable to contact lenses. Contact prescriptions include additional measurements:

• BC (Base Curve): The curvature of the lens back surface, matched to your cornea's shape.
• DIA (Diameter): The overall size of the contact lens.
• Brand: Unlike glasses lenses, contact lens power can vary slightly by material and manufacturer, so the brand is specified.

The power values may also differ numerically from your glasses prescription because contacts sit directly on the eye rather than at a distance from it. Always use the prescription your eye care provider wrote specifically for the lens type you intend to wear. For more on how lens categories differ, see our reference on contact lens types.

This article is for informational purposes only and is not a substitute for professional medical or optometric advice. Consult a licensed eye care provider for guidance specific to your vision needs.