Which auxiliary lens is used to extend the keratometer range to approximately 30.00D?

The correct choice, which is the -1.00 auxiliary lens, is used with a keratometer to extend its measurement range to higher corneal powers, allowing it to read up to approximately 30.00 Diopters. When a -1.00 lens is placed in front of the keratometer's optics, it effectively reduces the amount of light that is being refracted by the cornea. This means the keratometer can now calculate higher corneal curvatures by compensating for the negative value introduced by the auxiliary lens.

For example, if the cornea were to measure at 31.00D, adding a -1.00D lens results in a reading of 30.00D on the keratometer. This means that the keratometer can accurately measure higher degrees of corneal steepness, which is particularly useful in diagnosing and fitting contact lenses for patients with high astigmatism or abnormal corneal shapes.

Using other auxiliary lenses, like the -2.00D or any positive lenses, would not be effective for this purpose because they would either reduce the range too much or not allow for the necessary correlation for higher readings in the keratometers designed for standard ranges.