How much Corneal Astigmatism does a patient have when they have K readings of 42.25 and 43.75?

To determine the amount of corneal astigmatism a patient has based on their keratometry readings, you subtract the K reading of the flatter meridian from the K reading of the steeper meridian. In this case, the readings are 42.25 D for the flatter meridian and 43.75 D for the steeper meridian.

Calculating the difference:

43.75 D - 42.25 D = 1.50 D

This measurement indicates that the patient's corneal astigmatism is 1.50 diopters. Therefore, the correct answer reflects this difference in curvature between the two principal meridians of the cornea.

Recognizing that astigmatism arises from varying curvature on different axes, the calculated value of 1.50 D provides a precise characterization of the corneal shape and informs appropriate contact lens fitting or other corrective measures.