What indicates the amount of corneal astigmatism when using a keratometer?

The amount of corneal astigmatism can be determined using a keratometer by taking readings from the horizontal and vertical drums. The keratometer measures the curvature of the cornea in different meridians, typically aligning with the horizontal and vertical axes. By comparing these two measurements, you can determine the amount of astigmatism present.

When the horizontal and vertical readings are significantly different, it indicates that the cornea has varying curvatures in those meridians, which is the hallmark of astigmatism. If the readings are equal, it suggests that the cornea is symmetrical and not astigmatic.

Other options do not directly provide information related to measuring corneal astigmatism. For example, the smoothness of the lens surface does not reflect astigmatism levels but rather indicates the quality of the lens surface. The diameter of the lens is unrelated to the patient’s corneal shape and how it relates to astigmatism. The back vertex power measurement is also relevant for determining overall lens strength and vision correction but does not directly indicate the presence or degree of corneal astigmatism.