Keratometry measures the radius of curvature of the cornea to give a value of the corneal astigmatism. This is the most important astigmatism, but not the only one, since there is also astigmatism at the level of the posterior aspect of the cornea and that of the anterior and posterior faces of the lens, which in many cases is minimal. Astigmatism is the most frequent ametropia.

The automatic keratometers are the most used.

In most normal corneas, keratometry is accurate enough to adjust contact lenses or calculate the power of intraocular lenses (IOL). Keratometry is also useful for detecting irregular astigmatism, in which keratometric images can not overlap or form regular ovals. However, in some circumstances, such as keratoconus, corneal ectasias after radial keratotomy or alterations of the ocular surface, the optical properties of the cornea are affected in areas other than those measured in keratometry and therefore The diagnosis should be complemented with more specific ophthalmological tests.