The cornea is the clear, dome-shaped surface that covers the iris and pupil of the eye. In a normal eye, the cornea is smooth and evenly curved in all directions, allowing light to focus precisely on the retina, which creates clear vision.

When the cornea has an uneven curvature, light is bent incorrectly, leading to blurred or distorted vision. This condition is known as corneal astigmatism. Astigmatism can also occur in the lens of the eye (lenticular astigmatism), which sits just behind the cornea. In both cases—whether corneal or lenticular—objects at any distance may appear unclear, wavy, or doubled.

In addition to blurry vision, moderate to severe astigmatism may cause eye strain, squinting, headaches, and poor night vision. Since astigmatism is often hereditary, many people are born with it, although it can also develop after an eye injury, eye disease, or eye surgery.

The severity of astigmatism is measured in diopters, which represent the focusing power of the eye. A perfectly round cornea with no astigmatism measures 0 diopters.

Most people’s eyes are not perfectly round, and having up to 0.75 diopters of astigmatism is considered normal and usually does not require correction. Astigmatism between 0.75 and 2 diopters is classified as mild, while 2 to 4 diopters is considered moderate. Any measurement of 4 diopters or more is viewed as significant or “bad” astigmatism and often requires treatment.

In general, patients with 1.5 diopters or more of astigmatism benefit from correction through eyeglasses, contact lenses, or specialty lens options, depending on the individual’s visual needs.

Astigmatism treatment depends on its severity. Small amounts of astigmatism are usually easy to correct with either eyeglasses or contact lenses. For mild cases, eyeglasses are often preferred since they can be fitted with a special cylindrical lens prescription that counteracts the irregular curvature of the cornea, allowing light to focus properly on the retina.

However, moderate to high levels of astigmatism are more complex. Conventional soft contact lenses often fail to provide clear vision because they may rotate on the eye, leading to blurred or fluctuating vision even with the correct prescription. In such cases, specialty contact lenses—including toric lenses, rigid gas permeable (RGP) lenses, or scleral lenses—are often the most effective solution. These advanced lenses provide a stable fit, sharper vision, and greater comfort for patients with unique corneal shapes.

Yes, astigmatism can significantly affect night vision. Patients often experience glare, halos, light streaks, and starbursts around headlights or streetlights, making driving at night particularly challenging. These visual disturbances happen because light entering the irregularly curved cornea does not focus evenly, leading to distortion.

For those with astigmatism, wearing properly prescribed corrective lenses—especially at night—is essential for safe and clear vision. Specialty contact lenses or glasses designed for astigmatism can greatly reduce halos and glare, improving night driving comfort and safety.

In most cases, astigmatism occurs in both eyes, since it is often related to the natural shape of the cornea or lens. However, it is possible to have astigmatism in only one eye (known as unilateral astigmatism). This is less common and usually happens as a result of an eye injury, corneal scar, or past eye surgery.

If you notice vision distortion, blurriness, or strain in just one eye, it’s important to schedule a professional eye exam. Early detection ensures the best treatment—whether that’s eyeglasses, specialty contact lenses, or advanced vision correction options.

For personalized guidance about your astigmatism or other vision concerns, contact The Raleigh Contact Lens Institute for a free phone consultation at (919) 850-5910 or email hello@raleighcontactlens.com.