Astigmatism is a common vision condition where the eye has an irregular shape, preventing light from focusing properly on the retina. Wearing standard, or “regular,” contact lenses not designed for astigmatism can lead to various visual disturbances and discomforts.
Understanding Astigmatism and Contact Lenses
Astigmatism occurs when the cornea, the clear front surface of the eye, or the lens inside the eye has mismatched curves. Instead of a uniformly round shape, an astigmatic eye is shaped more like a football or an egg. This irregular curvature causes light rays to bend unevenly, focusing at multiple points instead of a single, sharp point on the retina, resulting in blurred or distorted vision.
Contact lenses are categorized by their design for vision correction. Spherical contact lenses, often called “regular” contacts, feature a uniform curvature across their entire surface. These lenses are typically prescribed to correct common refractive errors like nearsightedness (myopia) or farsightedness (hyperopia). Toric contact lenses, by contrast, are specifically designed to address astigmatism. They possess different refractive powers in their vertical and horizontal orientations, accommodating the varying curvatures of an astigmatic eye.
Why Spherical Lenses Fall Short for Astigmatism
Spherical lenses are designed to provide a consistent power across their entire surface, bending light to a single focal point for eyes with a symmetrical curvature. This design works well when the eye’s cornea or lens is uniformly curved, allowing light to converge precisely on the retina. However, an eye with astigmatism has different curves in different directions, making its shape more akin to a football rather than a perfect sphere.
When a spherical lens is placed on an astigmatic eye, it cannot uniformly correct for these differing curvatures. The lens applies the same focusing power across all meridians of the eye, which is insufficient for an eye that requires different amounts of correction along different axes. Consequently, light rays are not bent correctly to form a single, clear image on the retina, creating a smeared image.
Immediate Effects of Wearing Incompatible Lenses
Wearing spherical contact lenses with astigmatism leads to a lack of visual clarity. Vision remains blurry or distorted, appearing wavy or streaky, because the lens cannot properly focus light onto the retina. This constant struggle to achieve clear sight forces the eyes to work harder, leading to eye strain and fatigue.
The increased effort and strain on the eye muscles frequently result in headaches. These headaches often center around the eyes and can become persistent after tasks requiring prolonged visual concentration. Individuals may also experience general discomfort and eye irritation. Continued use of incompatible lenses can lead to worsening symptoms due to the sustained ocular strain.
Addressing Astigmatism with Proper Correction
For individuals with astigmatism, the most common and effective contact lens solution is toric lenses. These lenses are engineered with different powers in different meridians, precisely matching the unique curvatures of an astigmatic eye. Toric lenses also feature design elements, such as thicker zones, ballasting, or truncation, to help them maintain proper orientation on the eye with each blink, ensuring consistent and clear vision.
Other options are available, depending on the specific characteristics and severity of the astigmatism. Eyeglasses with specialized cylindrical lenses can also effectively correct astigmatism by providing different refractive powers along different axes. Rigid gas permeable (RGP) lenses are another choice, particularly for higher levels of astigmatism or irregular corneal shapes, as their rigid material can help create a more uniform refractive surface. Consulting an eye care professional is important for proper diagnosis and to determine the most suitable corrective option.