Understanding Astigmatism
Astigmatism is a common optical defect where an eye or a lens has different focal lengths for different meridians. This means that light entering the eye does not focus uniformly on the retina, typically because the cornea (the front surface of the eye) or the lens inside the eye has an irregular, non-spherical shape, often compared to a football instead of a perfectly round basketball.
How Astigmatism Affects Vision
In an astigmatic eye, instead of light rays converging to a single sharp focal point on the retina, they form two separate focal lines. This results in blurred, stretched, or distorted vision at all distances. Objects may appear to have ghosting or shadows, and certain orientations (like horizontal versus vertical lines) might appear clearer than others.
Practical Example of Astigmatism
A common symptom of astigmatism is seeing parts of an image clearly while other parts are blurry. For instance, when looking at a clock face, a person with astigmatism might see the lines at 12 and 6 o'clock sharply, but the lines at 3 and 9 o'clock appear unfocused, or vice-versa. This selective blurring makes tasks like reading fine print challenging.
Correction and Importance
Astigmatism is a widespread refractive error and can significantly impact visual clarity. Fortunately, it is easily correctable. Eyeglasses with cylindrical lenses, toric contact lenses, or refractive surgeries such as LASIK are used to compensate for the irregular curvature, redirecting light rays to a single focal point on the retina and restoring clear vision.