Keratometer (Ophthalmometers)

Keratometry is a technique used to measure of the anterior curvature of the cornea, which when damaged or misshapen causes a vision problem known as astigmatism. A keratometer works by reflecting an image off of two points in the cornea, and utilizes the relationship between object size, the size of the image reflected, and the distance between the object and the keratometer. The result is a minimum and maximum curvature value for the cornea. There are two types of keratometers: single position Helmholtz keratometers, which are more common, and can adjust image size; and Javal-Schiotz keratometers, two-position machines that adjust object size. Some all-in-one automatic optical test systems include keratometry capabilities, while stand-alone keratometers are typically manual. The latter are often preferred by more experienced ophthalmologists and technicians who can minimize error while subjectively reviewing the surface of the cornea.