What is a common Rx example for against-the-rule astigmatism?

In the context of astigmatism, there are three primary classifications based on the orientation of the cylindrical correction in relation to the principal meridians. Against-the-rule astigmatism occurs when the steepest corneal meridian is aligned vertically and the flattest is horizontal. This means that the highest degree of curvature (and resulting refractive error) is present in the vertical plane.

In the given choices, the prescription that best exemplifies against-the-rule astigmatism is characterized by a higher cylinder value at 090 degrees, indicating that the correction is oriented more along the horizontal meridian where the cornea is flatter. The presence of a spherical component that is negative, combined with a cylindrical component that also has a negative axis of 180 degrees, indicates the steepness (the curvature) is oriented vertically. This aligns perfectly with the condition of against-the-rule astigmatism, as the cylinder's orientation predicts that the primary refractive error resides in the vertical meridian.

Hence, the chosen prescription reflects the characteristics of against-the-rule astigmatism, confirming it as the correct answer in this multiple-choice setup.