How to Read Your Eyeglass Prescription (Without a Degree in Optometry)

You finally leave the eye exam with a printed prescription, glance at the page, and immediately wonder if it was written in another language. Tiny numbers, abbreviations, plus signs, minus signs, and mysterious columns can make even a simple prescription seem intimidating.

The good news is that you don't need medical training to understand what those numbers are telling you. Once you know what each section represents, your prescription becomes much easier to read—and you'll also feel more confident when shopping for new glasses or discussing lens options with your optician.

Every Prescription Starts With Two Eyes

Your prescription is divided into two sections:

• OD – Your right eye.

• OS – Your left eye.

Occasionally you'll also notice OU, which refers to both eyes together.

Each eye has its own measurements because it's perfectly normal for one eye to require a different correction than the other.

SPH: The Main Number

The Sphere (SPH) value is the first number most people notice.

This tells you the amount of lens power needed to sharpen your vision.

If the number begins with a minus (-) sign, you're nearsighted. Distant objects appear blurry because your eyes focus images slightly in front of the retina.

Example:

SPH -2.25

This indicates moderate nearsightedness.

If the number has a plus (+) sign, you're farsighted. Close objects may be more difficult to focus on.

Example:

SPH +1.50

This means your lenses help bring nearby images into clearer focus.

The farther the number is from zero, the stronger the prescription.

CYL: Correcting Astigmatism

Not everyone has a value listed under CYL.

This section measures the amount of astigmatism—a common condition caused by the eye having an irregular curve rather than a perfectly round shape.

Astigmatism doesn't mean there's something seriously wrong with your eyes. In fact, millions of people have it without realizing it.

A prescription might show:

CYL -0.75

or

CYL -2.00

Higher numbers indicate a greater amount of astigmatism correction.

If this field is blank, your eye doctor determined you don't need this correction.

AXIS: A Direction, Not a Strength

The Axis only appears when a CYL value is present.

Unlike the other numbers, Axis doesn't measure power. Instead, it identifies the exact orientation where the astigmatism correction should be placed inside the lens.

Axis ranges from 1 to 180 degrees.

For example:

CYL -1.25

Axis 90

This doesn't mean your vision is worse than someone whose axis is 45. It simply describes the angle needed to position the correction accurately.

ADD: Reading Help

If you're over forty, you may notice an ADD value.

This is the additional magnifying power used for:

• Progressive lenses

• Bifocals

• Reading glasses

For example:

ADD +2.00

This doesn't replace your distance prescription. Instead, it's added to the lower portion of multifocal lenses so close-up tasks become easier.

Prism: Used Less Often

Some prescriptions include Prism measurements.

Prism isn't related to blurry vision. Instead, it helps align the eyes when they don't work together perfectly.

These prescriptions are less common and are carefully customized for each patient.

Why Two Eyes Rarely Match

Many people expect identical prescriptions in both eyes.

In reality, differences are extremely common.

A prescription could look like this:

Right Eye

• SPH -1.75

• CYL -0.50

• Axis 170

Left Eye

• SPH -2.50

• CYL -1.25

• Axis 10

One eye may naturally require stronger correction than the other. Your brain combines both images into a single, clear picture.

Can You Judge Vision by the Numbers?

Not accurately.

Someone with a prescription of -6.00 isn't automatically seeing "twice as badly" as someone with -3.00.

Your prescription only measures how much correction your eyes need. It doesn't describe your overall eye health, retinal condition, depth perception, or visual comfort.

Two people with nearly identical prescriptions may have completely different visual experiences.

What a Prescription Doesn't Tell You

A glasses prescription focuses on lens power.

It doesn't specify:

• Lens material

• Blue light filtering

• Anti-reflective coating

• Scratch resistance

• Photochromic lenses

• Frame size

• Pupillary distance (sometimes provided separately)

These choices are made when ordering your glasses and can significantly affect comfort and durability.

Why Prescriptions Expire

Eyes change over time.

Even small changes can affect reading, driving at night, or computer work.

An expired prescription may still feel "good enough," but updated measurements usually provide sharper vision and reduce unnecessary eye strain.

Regular eye exams also help detect conditions that have nothing to do with glasses, including glaucoma, cataracts, and retinal disease.

Don't Try to Compare Prescriptions Online

It's tempting to search the internet for charts that label prescriptions as "mild," "moderate," or "severe."

Those comparisons can be misleading.

An optometrist considers far more than a single number, including:

• Your age

• Daily activities

• Eye coordination

• Previous prescriptions

• Overall eye health

• Visual symptoms

The prescription works as one complete set of measurements rather than isolated values.

Your prescription determines the lenses you need, but it doesn't determine the style of glasses you should wear. After understanding your prescription, take a few minutes to learn which frame shapes work best for your face. Our article on choosing eyeglass frames based on your face shape can help you select frames that are both comfortable and flattering. 

Reading Your Prescription With Confidence

Once you understand the abbreviations, an eyeglass prescription becomes much less mysterious.

• SPH determines your basic vision correction.

• CYL measures astigmatism.

• Axis positions that correction correctly.

• ADD provides extra magnification for near tasks.

• Prism helps align vision when needed.

These values work together to create lenses tailored specifically for your eyes. While it's helpful to understand what the numbers mean, your prescription is still best interpreted alongside a comprehensive eye exam. If anything on the form seems confusing, don't hesitate to ask your optometrist or optician—they're there to make sure you leave with both clear vision and a clear understanding of your eye care.