Types of Astigmatism: Myopic, Hyperopic & Mixed Astigmatism Explained
Astigmatism is a common refractive error of the eye that causes blurry or distorted vision. It occurs when the cornea or lens of the eye is not perfectly curved, so light entering the eye does not focus evenly on the retina. Instead of coming to a single sharp point, light rays are bent differently in different directions, which can make images appear stretched, blurred, or skewed.
There are several types of astigmatism, classified based on how light focuses inside the eye:
Regular astigmatism is the most common type, where the cornea curves more steeply in one direction than another, causing light to focus at different points either in front of or behind the retina.
Irregular astigmatism. In this kind of astigmatism, the cornea has an uneven shape due to scarring, injury, or conditions like keratoconus, causing more complex distortions of vision.
Myopic astigmatism. One or both focal points fall in front of the retina, often combined with nearsightedness.
Hyperopic astigmatism. One or both focal points fall behind the retina, often combined with farsightedness.
Mixed astigmatism – One focal point is in front of the retina and one behind, combining elements of both nearsighted and farsighted astigmatism.
This variability in how light is focused is why people with astigmatism often experience blurred or distorted vision at all distances, and why a proper eye exam is necessary to determine the exact type and prescription needed.
Myopic astigmatism happens when the eye’s cornea or lens curves unevenly, causing light to focus at one or more points in front of the retina instead of directly on it. Because the light converges too far in front of the retina, distant objects appear blurry or out of focus, while nearby objects may still be seen more clearly.
In this type of astigmatism, the uneven curvature means that different meridians of the eye bend light by different amounts. For example, one axis might focus slightly closer to the lens than another. The result is a combination of nearsightedness (myopia) and the distortion caused by astigmatism, making both distant clarity and overall sharpness harder to achieve without corrective lenses like glasses or contact lenses.
Hyperopic astigmatism occurs when the cornea or lens of the eye is shaped so that light focuses behind the retina instead of directly on it. This means that the eye struggles to bring nearby objects into sharp focus, making close-up tasks like reading or sewing more difficult, while distance vision may be less affected.
In hyperopic astigmatism, the uneven curvature of the cornea or lens causes different meridians of the eye to bend light by different amounts. As a result, some light rays converge behind the retina, producing blurred or distorted vision for near objects. People with this condition often experience eye strain or headaches when doing prolonged close-up work.
Mixed astigmatism occurs when the eye’s cornea or lens has an uneven curvature that causes one focal point to fall in front of the retina and another to fall behind it. Because of this, neither distant nor close-up objects are focused properly, leading to blurred or distorted vision at all distances.
In mixed astigmatism, different meridians of the eye bend light differently: one axis may behave like myopia (focusing in front of the retina), while the other behaves like hyperopia (focusing behind the retina). This combination makes both near and far vision challenging without correction. People with mixed astigmatism often notice general blur, distortion, and eye strain, and they usually require specially designed lenses like glasses, contact lenses, or refractive surgery to properly focus light onto the retina and achieve clear vision.
Astigmatism can arise from several factors, often related to the shape and structure of the eye. Common causes include:
Genetics. Many people inherit astigmatism from their parents. If a family member has irregular corneal or lens curvature, you are more likely to develop it as well.
Irregular corneal shape. The cornea, the clear front surface of the eye, may naturally have an uneven curvature instead of being perfectly round. This irregularity can cause light to focus unevenly, resulting in astigmatism.
Eye injuries. Trauma to the eye can alter the cornea or lens shape, leading to astigmatism. Even minor injuries or scars can affect how light enters the eye.
Certain eye conditions. Conditions like keratoconus, where the cornea thins and bulges into a cone shape, can cause irregular astigmatism. Cataracts or previous eye surgeries may also contribute to changes in corneal or lens shape, resulting in astigmatism.
Overall, astigmatism is usually the result of structural variations in the eye rather than lifestyle factors. Eye doctors can diagnose astigmatism through a combination of vision tests and measurements that evaluate how light focuses in the eye. Common diagnostic methods include:
Visual acuity test: Using a standard eye chart, the doctor checks how clearly you can see letters or symbols at various distances. Blurriness or distortion can indicate astigmatism.
Keratometry: This test measures the curvature of the cornea by shining a light on it and analyzing the reflection. Uneven curvatures suggest astigmatism.
Refraction test: The doctor uses a phoropter or automated instrument to determine the exact prescription needed to correct your vision. By switching lenses and asking which makes images clearer, they can identify the degree and type of astigmatism.
Corneal topography: A detailed mapping of the cornea’s surface provides precise information about its shape. This is especially helpful for detecting irregular astigmatism caused by conditions like keratoconus.
Retinoscopy: A light is shined into the eye to observe how it reflects off the retina. This helps estimate how light is focusing and whether astigmatism is present.
Treatment options for astigmatism include glasses, special contact lenses called toric lenses or vision correction procedures. Procedures that can correct astigmatism include:
LASIK (Laser-Assisted In Situ Keratomileusis) During LASIK, an eye surgeon creates a thin flap in the cornea and uses a laser to precisely remove small amounts of corneal tissue. By reshaping the cornea, the light entering the eye can focus correctly on the retina, reducing or eliminating astigmatism.
PRK (Photorefractive Keratectomy) Similar to LASIK but removes the outer layer of the cornea rather than creating a flap. Vision recovery takes longer, but it can be safer for thinner corneas.
SMILE (Small Incision Lenticule Extraction) A minimally invasive laser procedure that removes a small lenticule of corneal tissue to reshape the eye.
Toric intraocular lenses (IOLs) Used in cataract surgery, these lenses replace the eye’s natural lens and can correct astigmatism permanently.
If you experience persistent blurry vision, frequent headaches, or eye strain, it may be a sign of astigmatism or another refractive error. The sooner you schedule an eye exam, the sooner an eye doctor can determine the cause and recommend the right correction, whether through glasses, contact lenses, or advanced procedures like LASIK. Colorado Eye Surgeons is a trusted provider for diagnosing and treating astigmatism and other refractive errors. With expert eye doctors, state-of-the-art technology, and personalized care, they ensure accurate assessments and effective treatment options tailored to your vision needs. Seeking professional care not only improves clarity but also helps protect long-term eye health. Regular eye exams are key, especially if you notice changes in your vision or struggle with everyday tasks that require clear sight. Your eyes deserve expert attention, and Colorado Eye Surgeons offers the experience and technology to help you see your world clearly.
Schedule an eye exam today with Colorado Eye Surgeons.
