Eye health resources

How doctors measure the severity of your astigmatism

Astigmatism is a common vision issue that can range from mild to severe. Learn how your eye doctor determines the severity of your astigmatism and how the severity impacts treatment.

Medically reviewed on November 19, 2025

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Published on February 3, 2026

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5 minute read

Key takeaways

Astigmatism is when the eye is shaped like a football with two curves
Sphere (SPH) and cylinder (CYL) measure the two curves, and the higher the CYL number, the more severe the astigmatism
CYL prescriptions higher than –3.00 may require specially ordered lenses

Astigmatism, explained

Eyes tend to work best when the cornea (clear front part of your eye) and the lens are perfectly round, like a smooth basketball. That way, light is able to focus on one point inside the eye because it passes through a consistent curvature. With astigmatism, the cornea or lens inside your eye is shaped more like a football, which has two different curves. Since there is more than one curve, light cannot focus to one sharp point on the retina. Instead, it may focus on two or more points in the eye. This can make things look blurry or stretched at near and far distances.

Understanding your astigmatism prescription

Your astigmatism prescription has 3 main parts:

Sphere (SPH)

When you have astigmatism, your “sphere” prescription only covers part of your vision correction. A plus (+) sign indicates farsightedness, while a minus (-) sign indicates nearsightedness. The higher the number, the stronger the correction.

Cylinder (CYL)

This shows how much correction you need for your astigmatism (an eye shape that's more like a football than a basketball). A higher number means more correction.

Axis

The final piece of a prescription for astigmatism is the axis, which measures the orientation of your astigmatism. Axis tells your eye doctor whether your astigmatism is horizontal (180), vertical (90) or somewhere in between. Your axis can also affect how things look.

When the astigmatism is on a 180 axis, like a football laying on the ground, your vision may be distorted in a way that makes things look taller
When astigmatism is on a 90 axis, like a football standing tall, your vision may look “smeared” right to left
When your astigmatism is between 90 and 180 degrees, like a tilted football, your vision may look “smeared” diagonally

Knowing the axis of your astigmatism helps your eye doctor choose lenses that focus light in the right direction so your vision stays clear and sharp.

The types of astigmatism

Is there an astigmatism severity scale?

While there isn’t a severity scale used across the board for all eye doctors, patients often ask how severe their astigmatism is, and some common numbers may look like this:

Insignificant (-0.25 to –0.50 diopters)

Astigmatism at these levels may not be noticeable.

Low (-0.75 to –1.00 diopters)

Many people have this level of astigmatism and barely notice it.

Moderate (-1.25 to –2.25 diopters)

Glasses or toric contact lenses often help provide clearer vision at these levels.

High or severe (-2.50 and above)

This level can cause noticeably blurred or distorted vision and often needs stronger or specialized lenses when the prescription is above –3.00 diopters.

How do eye doctors treat severe astigmatism?

If astigmatism is moderate to severe, doctors have a few common options:

Glasses with cylindrical lenses

This is the most common and easiest option for correcting astigmatism.

Toric contact lenses

These soft or rigid gas permeable lenses are made to sit in a certain orientation and correct both sphere and cylinder. For levels above 2.50 diopters, your lenses may need to be custom-made.

Scleral or specialty rigid lenses

These larger lenses rest on the white part of the eye (the sclera) and create a smooth surface for clear vision , and are often used for very irregular corneas.

Laser and other surgeries

Laser surgery and others forms of surgeries can be used to reshape the cornea to correct astigmatism. Your eye doctor will recommend what is safe for your eyes and fits your lifestyle.

Treatment options for astigmatism

When to see your eye doctor

If your vision feels blurry, you have headaches, or your current glasses or contacts no longer give clear sight, it’s time to make an appointment. Your eye doctor can measure your prescription, including your astigmatism and share what your numbers mean for daily life. Children should have eye examinations too even if they seem to be seeing well. Untreated astigmatism can affect reading and schoolwork and sometimes lead to amblyopia (lazy eye).

Find an eye doctor

FAQs

Frequently asked questions

What is a bad astigmatism axis?

There is not an axis that is worse than others, axis simply measures the orientation of your astigmatism. “Bad” or “severe” astigmatism is when the cylinder (CYL) measurement is around 2.50 or higher, indicating a steep astigmatism that will distort your vision strongly.

How is astigmatism measured?

The test combines instrument readings and patient responses through devices like a phoropter and keratometer. Together these give the cylinder (strength) and axis (orientation).

How to measure astigmatism at home?

You can’t accurately measure astigmatism at home. If you notice blurry or smeared lines on an eye chart, see an eye doctor for a full exam.

Can astigmatism change over time?

Yes. Astigmatism can change as the eye grows or after injury or surgery. It usually stabilizes in early adulthood but should be checked regularly.