Have you ever looked at your eye prescription and wondered what all those numbers and abbreviations mean? You're not alone! Eye prescriptions can seem confusing at first, but understanding them is crucial for maintaining good eye health and ensuring you get the right glasses or contact lenses. In this guide, we'll break down the components of an eye prescription in simple terms, explain common vision conditions, and help you decipher your prescription step-by-step.

Key Components of an Eye Prescription

When you receive an eye prescription from your optometrist, it typically includes several key components. Let's explore what each part means.

OD and OS: Understanding Eye Abbreviations

The abbreviations OD and OS are Latin terms used in eye care. OD stands for "oculus dexter," which means "right eye," and OS stands for "oculus sinister," which means "left eye." Sometimes you might also see OU, which stands for "oculus uterque" and refers to both eyes.

SPH (Sphere)

The SPH value indicates the amount of lens power, measured in diopters, needed to correct nearsightedness or farsightedness. A negative number (-) indicates nearsightedness (myopia), meaning you have trouble seeing distant objects. A positive number (+) indicates farsightedness (hyperopia), meaning you have trouble seeing close objects.

CYL (Cylinder) and Axis

The CYL value is used to correct astigmatism, which is an irregular curvature of the cornea or lens. The CYL number can be positive or negative and measures the lens power needed to correct astigmatism. The axis value, ranging from 0 to 180 degrees, indicates the orientation of astigmatism. Together, CYL and axis ensure that the correction is properly aligned with your eye's shape.

ADD (Addition)

The ADD value is commonly found in prescriptions for bifocals or progressive lenses. It represents the additional magnifying power needed for reading or close-up work. This value is always positive and is added to the SPH value for near vision correction.

PD (Pupillary Distance)

PD measures the distance between the centers of your pupils in millimeters. This measurement is crucial for ensuring that the lenses in your glasses are correctly aligned with your eyes, providing clear and comfortable vision.

Common Vision Conditions

Understanding common vision conditions can help you make sense of your prescription. Here are some of the most frequent conditions:

Nearsightedness (Myopia)

Myopia occurs when the eyeball is too long or the cornea is too curved, causing light to focus in front of the retina. This makes distant objects appear blurry. Myopia is indicated by a negative SPH value in your prescription.

Farsightedness (Hyperopia)

Hyperopia happens when the eyeball is too short or the cornea is not curved enough, causing light to focus behind the retina. This results in difficulty seeing close objects clearly. Hyperopia is indicated by a positive SPH value in your prescription.


Astigmatism is caused by an irregular shape of the cornea or lens, leading to distorted or blurred vision at all distances. It is corrected with a CYL value and an axis value in your prescription.


Presbyopia is an age-related condition where the eye's lens becomes less flexible, making it difficult to focus on close objects. This condition usually affects people over 40 and is corrected with an ADD value in the prescription.

Reading Your Eye Prescription

Deciphering your eye prescription can be straightforward if you understand the key components. Here’s a step-by-step guide:

  1. Identify OD and OS: Determine which values correspond to your right eye (OD) and left eye (OS).

  2. Read the SPH value: Check the SPH value for each eye to see if you are nearsighted (negative number) or farsighted (positive number).

  3. Look at the CYL and Axis: If you have astigmatism, find the CYL value and the corresponding axis value. These will help correct the irregular curvature in your eyes.

  4. Check the ADD value: If you have presbyopia, the ADD value will indicate the additional power needed for reading or close work.

  5. Measure the PD: Ensure the PD is listed, as this measurement is crucial for properly aligning your lenses with your eyes.

Let’s look at an example prescription to put this into practice:

  • OD: -2.00 SPH, -1.00 CYL, 90 Axis
  • OS: -1.50 SPH, -0.75 CYL, 80 Axis
  • ADD: +1.50
  • PD: 63 mm

For the right eye (OD), the prescription indicates moderate nearsightedness (-2.00 SPH) with mild astigmatism (-1.00 CYL) at a 90-degree axis. The left eye (OS) shows mild nearsightedness (-1.50 SPH) with slight astigmatism (-0.75 CYL) at an 80-degree axis. The ADD value (+1.50) indicates additional reading correction, and the PD (63 mm) ensures proper lens alignment.

Frequently Asked Questions

What Does It Mean if I Have a Negative or Positive SPH?

A negative SPH value means you are nearsighted and have difficulty seeing distant objects clearly. A positive SPH value indicates you are farsighted and struggle with seeing close objects.

How Often Should I Get My Eyes Checked?

It is generally recommended to have an eye exam every one to two years, depending on your age, health, and whether you wear glasses or contact lenses. Regular check-ups are important for maintaining eye health and updating your prescription as needed.

Can My Prescription Change Over Time?

Yes, your prescription can change over time due to factors such as age, health conditions, and lifestyle changes. Regular eye exams help monitor these changes and ensure your vision correction is up-to-date.

May 30, 2024 — Glasseslakoh