Which prescription indicates against-the-rule astigmatism?

Against-the-rule astigmatism occurs when the steepest meridian of the cornea is oriented horizontally, typically at 30 degrees to 150 degrees. In this type of astigmatism, the prescription reflects a greater power in the vertical meridian compared to the horizontal meridian.

Option A presents a prescription with a power of -4.50 diopters in the sphere and a cylinder of +1.00 diopters at an axis of 75 degrees. The axis indicates that the steepest meridian is positioned at 75 degrees, which is closer to horizontal than vertical. Since the sphere power is negative and the cylinder power is positive, this configuration signifies that the steepest meridian (the +1.00) is contributing to the reduction of vision primarily in the horizontal direction, thus defining it as against-the-rule astigmatism.

Understanding the orientation of the axes and the relationships between the spherical and cylindrical values is key in identifying types of astigmatism. This knowledge allows practitioners to determine how to correct vision effectively based on the characteristics of astigmatism detailed in the prescription.