What pattern is associated with against the rule astigmatism?

Against the rule astigmatism is characterized by the orientation of the corneal steepest meridian being vertical, which results in a specific optical pattern known as the "bow-tie" pattern. In this context, the steepest curvature is aligned vertically and the flattest curvature is aligned horizontally, creating a shape that resembles a bow tie when viewed on a topographic map of the cornea. This pattern is essential to understand when fitting contact lenses, as the design must align properly with the corneal shape to correct the refractive error effectively.

The "bow-tie" description is a fundamental concept in the study of astigmatism because it visually represents how light behaves when it passes through the cornea with this type of refractive error. Proper identification of this pattern allows eye care professionals to design and prescribe the most effective lens types to accommodate the needs of patients with against the rule astigmatism.