Astigmatism is a common vision condition where the eye struggles to focus light correctly onto the retina. It results from an irregular curvature in the eye’s cornea or lens. As a refractive error, the eye does not bend light properly to create a clear image. This condition affects many people and can occur alongside other refractive errors like nearsightedness or farsightedness.
Understanding Astigmatism
Astigmatism involves an eye shape that is not perfectly spherical. Instead of a uniformly curved surface like a basketball, an eye with astigmatism has a cornea or lens shaped more like an American football or the back of a spoon. This irregular curvature means light entering the eye is not focused equally in all directions.
When light rays pass through an eye with astigmatism, they bend differently along various meridians, or planes, of the eye. Instead of converging at a single focal point on the retina, light rays meet at multiple focal points. This spreading of light prevents the formation of a clear image, leading to distorted vision.
How Astigmatism Impacts Vision
Blurred or distorted vision is a primary impact of astigmatism, occurring at any distance and making both near and far objects appear unclear. This blurring often manifests as a stretching or smearing of images, rather than just a general fuzziness.
Individuals with astigmatism may also experience difficulties with night vision. Glare from headlights or streetlights can seem exaggerated, and halos may appear around light sources, making nighttime driving challenging. Eye muscles may work harder to compensate for unfocused vision, leading to symptoms such as eye strain, fatigue, and headaches, particularly after prolonged visual tasks like reading or computer use.
What Causes Astigmatism
Astigmatism is most frequently present from birth, indicating a strong congenital component. Many individuals are born with some degree of corneal astigmatism. Genetic factors play a significant role, as the condition often runs in families, suggesting an inherited predisposition to the specific eye shape.
While often congenital, astigmatism can also develop or change over time, progressing gradually during childhood or early adulthood. Less common causes include eye injury, which can alter the cornea’s shape through scarring, or certain eye diseases affecting corneal integrity. Additionally, some eye surgeries, such as cataract removal, can induce or modify existing astigmatism.
Options for Correcting Astigmatism
Corrective eyeglasses are a common and effective way to manage astigmatism. These glasses use special cylindrical lenses that compensate for the eye’s irregular curvature. The cylindrical power in the lens is precisely oriented to counteract the uneven focusing of light, directing light rays to converge correctly on the retina.
Contact lenses also offer a solution for astigmatism, specifically through toric contact lenses. Unlike standard spherical lenses, toric lenses have different powers in different meridians, much like the astigmatic eye. They are designed to stay in a specific orientation on the eye to properly correct irregular focusing. Toric lenses come in both soft and rigid gas permeable (RGP) varieties.
For a more permanent correction, various refractive surgeries can reshape the cornea to improve the eye’s focusing ability. Procedures like LASIK (Laser-Assisted In Situ Keratomileusis) and PRK (Photorefractive Keratectomy) use an excimer laser to precisely remove microscopic amounts of corneal tissue. This reshaping creates a smoother, more uniform corneal surface, allowing light to focus correctly on the retina. SMILE (Small Incision Lenticule Extraction) is another laser-based option, involving creating a small, lens-shaped piece of tissue within the cornea that is then removed through a tiny incision. These surgical methods aim to reduce or eliminate the need for glasses or contact lenses.