What is Astigmatism?
Astigmatism is a common refractive error that causes blurred or distorted vision. It occurs when the front surface of the eye (the cornea) or, less commonly, the lens inside the eye is not perfectly round. Instead of having the same curvature in all directions, one meridian is steeper than the other.
As a result, light entering the eye does not focus on a single sharp point on the retina. Instead, it may focus on more than one plane, which can make vision appear blurred at near, far, or both distances. Astigmatism can occur on its own or alongside other refractive errors such as myopia (shortsightedness) or hyperopia (longsightedness).
What Causes Astigmatism?
Astigmatism is often described as two broad categories.
- Regular Astigmatism: In regular astigmatism, the most common form, the two principal meridians sit at right angles to one another. This predictable pattern means the condition responds well to correction through spectacles, toric contact lenses, or refractive surgery.
- Irregular Astigmatism: Here, the principal meridians are not perpendicular, and the corneal surface curves unevenly across multiple directions. Keratoconus, corneal scarring, prior eye surgery, and eye trauma are common underlying causes.
Because the optical distortion is less uniform, standard spectacles often fall short. Rigid gas permeable (RGP) or scleral contact lenses tend to deliver better outcomes, as they establish a smooth, consistent refracting surface across the cornea.
How is Astigmatism Corrected?
The right approach depends on the type and severity of astigmatism, the patient’s prescription, and their day-to-day requirements.
- Spectacles: The most widely used solution for regular astigmatism. Cylindrical or toric lenses compensate for the cornea’s uneven curvature, directing light more accurately onto the retina.
- Contact Lenses: Toric soft lenses are the most common prescription for regular astigmatism, engineered to hold a fixed orientation on the eye and maintain consistent correction. For irregular astigmatism, Rigid Gas Permeable (RGP) or scleral lenses are typically preferred. By forming a new optical surface over the cornea, they can achieve clarity that spectacles alone often cannot fully provide.
- Refractive Surgery: LASIK and PRK reshape the cornea directly, potentially eliminating (or significantly reducing) astigmatism and lessening reliance on corrective eyewear.
Candidacy isn’t universal. Suitability is assessed against factors such as astigmatism type and degree, corneal thickness, general eye health, and prescription stability, all evaluated through a thorough eye examination.