How to read an eyeglass prescription

How often should you get an eye exam to review the effectiveness of your prescription eyeglasses? It's that time of year again - it's time to update your prescription and visit the optometrist for your eye examination. But this year it will be different. This time, when you get your prescription, you will no longer be confused about what those characters and numbers mean!

The various components of an eye prescription can be complicated, but we'll explain them all so you know how to read glasses prescription, even if your prescription changes. Remember, it takes time to adjust to new glasses, so if your prescription has changed, or you use your glasses insurance to buy a new pair, it’s normal to have an adjustment period of a few days.

Glasses prescription chart

Your eyeglass prescription likely resembles a small grid or chart with rows, columns, and cells, whether it is written on paper or displayed digitally. The chart uses a confusing mixture of full words, positive and/or negative numbers, and letter abbreviations.

But how do you read an eye prescription? How should you interpret each of the eye prescription items’ meanings? To learn more about each term, refer to the glossary below, where you will find each of the abbreviations and numbers of the glasses prescription explained.

Eyeglass prescription numbers

Generally speaking, your prescription for vision correction will be represented as a positive or negative number, where the more your prescription number deviates from zero, the worse your vision is and the more vision correction (stronger prescription) you require.

You are farsighted if there is a "plus" symbol (+) in front of the number; you are nearsighted if there is a "minus" sign (-). These figures stand for diopters, the measurement unit for the corrective or focusing power of the lens that your eye needs. "D" is a common abbreviation for diopter.

These values are indicated in the S or SPH eye prescription for the "Spherical" part of the prescription.

Axis eye prescription

If you have astigmatism, there will be three numbers in your prescription. S x C x Axis is the general format for writing these numbers.

What is CYL in an eye prescription? The CYL or C can either be a negative or positive number and stands for the "cylinder" or astigmatism. Diopters are used to measure how much astigmatism a person has. The more astigmatism is present, the higher this value. Astigmatism is most commonly caused by a cornea that resembles a football rather than a basketball.

Axis is a number between 0 and 180 degrees. It displays how astigmatism is oriented. It is necessary to understand where the difference in curvature is occurring; it is not sufficient to state the amount of astigmatism present.

OD vs OS in prescriptions

The OD and OS abbreviations are both Latin acronyms that stand for the left and right eyes, respectively: OS left eye (oculus sinister) and OD right eye (oculus dextrus). There are times when you'll encounter the symbol OU, which denotes anything involving both eyes. For both of these abbreviations, you will find numbers listed in the prescription to indicate the strength of the correction necessary to focus light properly inside the eye.

Other important abbreviations include:

• NV: Near vision: (seeing things close-up).
• DV: Distance vision (seeing things far away).
• PD: Pupillary distance or the gap between your pupils is called your pupillary distance, drumroll, please. It's a measurement that aids in lining up the lens's center with your pupils' centers for the most precise eyesight possible. The pupillary distance can be measured by hand or with a pupillometer.
  In a perfect world, your eye doctor would always write your PD on your prescription. However, not all medical professionals follow this practice. You can always measure your pupillary distance online with our convenient tool.
• Prism: When eyes don't move in unison with one another, symptoms like double vision might occur. One condition that results in eye misalignment is strabismus, also referred to as "crossed eyes."
  Your doctor can modify your lenses with a prism to account for this condition. Your prescription, which also specifies the direction of the prism's thickest edge or base, determines the position and orientation of the prism indicated by BU (base up), BD (base down), BI (base in), or BO (base out).

We hope this detailed guide makes it a snap to read and understand your eyeglasses prescription. If you still need help or have any questions, please contact us.