Which astigmatism is described as having greater power in the horizontal meridian?

The concept of astigmatism involves the curvature of the cornea or lens in the eye, which can lead to blurred vision. When discussing astigmatism that exhibits greater power in the horizontal meridian, we refer to "with-the-rule astigmatism."

In with-the-rule astigmatism, the vertical meridian is weaker, and the horizontal meridian has greater power, indicating that light rays coming from vertical fields are focused at a different point than those coming from horizontal fields. This condition is typically linked with a vertical cylindrical lens prescription, which corrects the greater curvature in the horizontal direction.

Against-the-rule astigmatism, on the other hand, occurs when the horizontal meridian is weaker, and the power is greater in the vertical meridian. Mixed astigmatism incorporates a combination of both with-the-rule and against-the-rule characteristics, meaning one meridian is myopic (nearsighted) while the other is hyperopic (farsighted). Irregular astigmatism features curvature that varies in an unpredictable manner, making it different from the predictable patterns seen in the other types.

Understanding these distinctions helps eye care professionals provide appropriate prescriptions and treatments for patients with astigmatism,