What Is Astigmatism? A Complete Guide to Causes and Treatment

What is Astigmatism?

Astigmatism is a common refractive error that affects how your eye focuses light. In a normal eye, the cornea and lens are evenly curved, like a basketball. With this condition, the cornea or lens is irregularly shaped, more like a football, so light focuses unevenly on the retina. The result is blurry or distorted vision at any distance, since the eye cannot bring a single point of light into sharp focus.

Types of Astigmatism

There are two main ways to describe it: where it occurs, and how evenly the curve is distorted.

• Corneal: The front surface of the eye, the cornea, has mismatched curves.
• Lenticular: The lens inside the eye has mismatched curves instead of the cornea.
• Regular: The steepest and flattest curves meet at right angles; this is the most common pattern and the easiest to correct with standard lenses.

Irregular: The curve varies unevenly across the eye’s surface, often due to an eye injury, prior surgery, or a condition like keratoconus, and may need specialized contact lenses for full correction.

Common Astigmatism Symptoms

With the naked eye, you likely will not notice astigmatism in your own eyes or in someone else’s. Like nearsightedness or farsightedness, it is not a visibly obvious condition, but you may notice:

• Blurry or distorted vision at any distance
• Eye strain or discomfort
• Squinting to see near or far objects
• Difficulty focusing on printed words
• Double vision
• Headaches
• Difficulty with night vision

If any of these sound familiar, schedule an eye exam so your optometrist can test for it directly.

Image source: Kowa Optimed Eye Care

Causes and Risk Factors

This condition is so common that almost everyone has it to some degree, and astigmatism can increase or decrease with age. Genetics plays the largest role, and a family history raises your likelihood of developing it. Other causes and risk factors include:

• Eye injury or trauma that alters the shape of the cornea
• Eye surgery that is not performed with a perfectly even result
• Keratoconus, a progressive condition that thins and bulges the cornea
• Existing high nearsightedness or farsightedness
• General eye disease affecting the cornea or lens

Diagnosis and Eye Examination 

A comprehensive eye exam is the only way to confirm a diagnosis. Your eye doctor may use several tests, including:

• Visual Acuity: The standard distance chart test most people are familiar with.
• Keratometry: Measures your cornea’s curvature by focusing a circle of light on it and reading the reflection.
• Refraction: Uses a phoropter to test a series of lenses in front of your eyes, narrowing in on the prescription that gives the clearest vision.
• Corneal Topography: A detailed, color-coded map of your cornea’s surface, often used for more irregular cases or before certain surgeries, to pinpoint exactly where and how the curve is distorted.

Reading Your Prescription

If you have an astigmatism correction, your prescription will include both CYL and AXIS values for one or both eyes. The CYL number is a plus or minus value showing the strength of the correction. The AXIS number, a whole number between 1 and 180, shows the angle at which the cylinder sits on your lens. If you see a CYL value without an AXIS number, contact your eye doctor, as this is likely a prescription error.

Treatment and Correction Options

Astigmatism is highly correctable in most cases. The most common option is prescription glasses or toric lenses, which have different powers across different meridians of the lens to compensate for the eye’s irregular curve. Toric contact lenses work the same way and must be fitted precisely to stay properly positioned. For some people, refractive surgery such as LASIK or PRK can reshape the cornea for a more permanent correction, and orthokeratology, which uses specialized contact lenses worn overnight to reshape the cornea temporarily, is another option some eye doctors offer for mild to moderate cases. Your eye care provider can help you choose the approach that best fits your prescription and lifestyle.

Ordering Glasses With Your Prescription

Zenni can correct up to +/-6.00 CYL, and most of our lenses accommodate this correction, so you still have plenty of frame options. Single-vision lenses carry an extra-strength charge when a prescription indicates a strong correction, since they are more complex to produce. Bifocal and progressive lenses with high CYL numbers do not carry this extra charge.

Maintaining Healthy Vision

Regular eye exams are essential to monitor your condition and keep your prescription current. A few daily habits can also help reduce eye strain: take frequent screen breaks, ensure proper lighting while reading, stay hydrated, and eat a nutrient-rich diet that supports eye health.

Understanding your astigmatism is the first step toward clearer, more comfortable vision. Whether you need glasses, contacts, or a conversation with your eye doctor about surgical options, Zenni’s newest eyeglasses frame styles accommodate your prescription without sacrificing style. Browse new eyeglasses and find your next pair.

About the Author: Dr. Mori Ahi, O.D.

Dr. Mori has over 10 years of experience in eye care. She earned her undergraduate degree from UCLA and her optometry degree from the New England College of Optometry. She has worked in a variety of eye care settings and is passionate about helping her patients find a great pair of affordable glasses

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