What Is an Eye Prescription? How to Read Your Prescription and Understand Your Vision Before Getting Glasses

An eye prescription indicates the lens power required to correct vision problems, including myopia, hyperopia, and astigmatism. It is determined through an eye examination using specialised equipment together with a professional assessment.

Many people think of an eye prescription as simply a set of numbers used to make glasses. In fact, these figures reflect how light is refracted inside the eye, which affects the clarity of vision at different distances. A proper examination helps you choose glasses or contact lenses that better suit your everyday needs.

In practice, an eye prescription is usually shown on an eye prescription form and used as a reference when ordering prescription lenses. Your prescription may change with age, visual habits, and eye health, so regular eye examinations are recommended to ensure it still matches your current vision.

What Is a Diopter?

A diopter (D) is the standard unit used to measure lens power and indicate prescription values. The higher the number, the stronger the lens power required.

In general:

• A minus (-) value indicates myopia.
• A plus (+) value indicates hyperopia.
• A value of 0.00 indicates no refractive correction is required in that part of the prescription.

For example:

• A prescription of -1.25 indicates 1.25 diopters of myopia.
• A prescription of +2.00 indicates 2.00 diopters of hyperopia.

The Eye Examination Process

An accurate eye prescription is not based on an automated test alone. It is a combined process that uses specialised equipment and professional assessment to determine the prescription that best supports each person’s real-world vision, particularly for people with myopia, hyperopia, or astigmatism.

A typical eye examination includes:

• Reviewing your vision history, symptoms, and visual habits
• Measuring refractive error with an auto refractometer
• Using trial lenses to identify the prescription that provides the clearest vision
• Assessing astigmatism and performing further tests when needed
• Checking the balance of vision between the right and left eyes
• Evaluating distance and near vision
• Providing an eye prescription for glasses or contact lens consideration

A detailed examination can identify myopia, hyperopia, and astigmatism in one session. It can also help reduce the likelihood of eye strain, dizziness, or unclear vision after changing to a new pair of glasses.

An examination by an optometrist is another important factor in ensuring that your prescription is assessed carefully and suits your individual visual needs.

What Does an Eye Prescription Include?

After an eye examination, you will receive an eye prescription containing several letters and numbers. It may look complicated at first, but once you understand what each value means, it becomes easier to read and helps explain why every person’s lenses are different.

A typical eye prescription includes the following:

RE/LE or OD/OS

RE (Right Eye) or OD (Oculus Dexter) refers to the right eye.

RE (Right Eye) or OD (Oculus Dexter) refers to the right eye.

Although the abbreviations differ, they refer to the same eye positions. The format may vary depending on the clinic or optical store.

Sphere (SPH)

SPH is the main prescription value. It indicates the lens power needed to correct myopia or hyperopia.

A simple way to read SPH is:

• A minus (-) value indicates myopia.
• A plus (+) value indicates hyperopia.
• A value of 0.00 indicates no refractive correction is required in this part of the prescription.

For example:

• -1.25 indicates 1.25 diopters of myopia.
• +2.00 indicates 2.00 diopters of hyperopia.

This is why people often ask whether myopia or hyperopia uses a plus or minus value—the answer can be found in the SPH field.

Cylinder (CYL)

CYL indicates the degree of astigmatism. If you do not have astigmatism, this field may be left blank or shown as 0.00.

For people with astigmatism, CYL works together with the Axis value to ensure the lens corrects vision accurately. If you are unsure whether you have astigmatism, a detailed eye examination is recommended.

Axis

Axis indicates the orientation of astigmatism and ranges from 1 to 180 degrees. The Axis value has no meaning without a CYL value because it only specifies the direction of astigmatism.

For example:

CYL = -1.00

Axis = 90°

This means there is 1.00 diopter of astigmatism at an axis of 90 degrees.

Add

Add is the additional lens power needed for near vision. It is commonly found in people beginning to experience presbyopia, which usually develops after around age 40.

For example:

Add +1.50

This means an additional 1.50 diopters of lens power is required for reading or other close-up tasks. People with an Add value may be advised to use multifocal lenses, depending on their visual needs.

If near vision becomes difficult, choosing progressive lenses should be based on your prescription results and real-life visual habits to support smooth vision across all distances.

Prism

Prism is used to correct vision problems caused by an imbalance in the way the two eyes work together. It does not appear on every prescription and is only included when there is an indication, such as:

• Double vision
• Eye misalignment
• Abnormal eye coordination

Determining a Prism value requires a detailed examination so that the lenses can help address these symptoms appropriately.

Understanding the elements of an eye prescription—RE/LE, SPH, CYL, Axis, Add, and Prism—makes it easier to read your own results and make informed decisions when choosing glasses, lenses, and options that suit both your lifestyle and budget.

How to Read an Eye Prescription and Choose the Right Lenses

Reading an eye prescription is easier when you understand the meaning of each field. These values indicate your visual characteristics and the lens power appropriate for you, whether you have myopia, hyperopia, astigmatism, or difficulty with near vision.