Keratometer
（重定向自Ophthalmometer）
![An eye doctor examining a patient with a keratometer](/Images/godic/202501/31/Eye_doctor_examining_Nigerian_patient_with_keratometer5226.jpg")
A keratometer, also known as a ophthalmometer, is a diagnostic instrument for measuring the curvature of the anterior surface of the cornea, particularly for assessing the extent and axis of astigmatism. It was invented by the German physiologist Hermann von Helmholtz in 1851, although an earlier model was developed in 1796 by Jesse Ramsden and Everard Home.