Keratometry (K) is the measurement of the corneal curvature; corneal curvature determines the power of the cornea. Differences in power across the cornea (opposite meridians) results in astigmatism; therefore, keratometry measures astigmatism. It can be acquired with a variety of instruments either manually or via automated methods. Measurements can be very sophisticated, such as with topographers, that measure a cornea across a broad number of points, or it can be measured in a more finite area of the cornea, for example with a manual keratometer or with the IOL Master (Carl Zeiss Meditec). The IOL Master also measures the axial length and other ocular parameters (such as anterior chamber depth and white-to-white measurements) and includes K readings.