What astigmatism will cause the square to appear slightly elongated in the vertical meridian when viewed through spectacles?

The situation described involves viewing a square through spectacles and observing an elongation in the vertical meridian. This effect is typically associated with "against the rule" astigmatism. In this case, the steepest curvature of the cornea is oriented horizontally, meaning that the lens is designed to correct this irregular curvature, resulting in distortion when viewing objects oriented vertically, such as a square.

When individuals with against the rule astigmatism look at a square, the vertical edges will appear elongated, as their vision is predominantly corrected for the horizontal lines, causing the vertical lines to appear stretched or less sharp. This optical phenomenon is a direct result of the irregularities in the visual pathway created by the steepness of the astigmatism aligned against the rule, which is the inverse of what would be seen in with the rule astigmatism, where the distortion would be expected in the horizontal direction. Therefore, the correct answer reflects the influence of this specific orientation of astigmatism on visual perception.