Given the keratometric reading of 41.50@ 90/ 45.62@ 180, what type of astigmatism is indicated?

The keratometric readings provided indicate the curvature of the cornea in two principal meridians. The first reading shows a flatter curvature of 41.50 diopters at 90 degrees, while the second reading shows a steeper curvature of 45.62 diopters at 180 degrees. This difference in curvature suggests the presence of astigmatism.

The key to determining the type of astigmatism lies in the comparison of the steep and flat meridian orientations. With-the-rule astigmatism occurs when the steepest meridian is aligned with the vertical (90 degrees), which is not the case here. In contrast, against-the-rule astigmatism occurs when the steepest meridian is aligned with the horizontal (180 degrees), again not corresponding to the provided measurements.

Since the flat meridian is at 90 degrees and the steep meridian is at 180 degrees, this configuration indicates against-the-rule astigmatism. The alignment of the steep curvature at 180 degrees means there is greater power horizontally compared to the vertical, which is the defining feature of this type of astigmatism. Thus, the correct conclusion based on the given keratometric values is indeed against-the-rule astigmat