Trained as a physician and surgeon by the Prussian army, Hermann von Helmholtz
invented the keratometer (or ophthalmometer) in 1854—four years after his invention of the
ophthalmoscope. Despite his many contributions to ophthalmology, Helmholtz never had
a private medical practice nor did he ever practice eye medicine.
As a professor of physiology, anatomy, and physics, Helmholtz was familiar with the heliometer, an
instrument used since the 18th century to measure the diameter of the sun. His keratometer applied
the principles of the heliometer for use in measuring the curvature of the eye.
Helmholtz’s keratometer was later modified by Louis Emile Javal and Hjalmar Schiotz so it could be used
in the doctor’s office. Manufactured by E.B. Meyrowitz, the Javal-Schiotz instrument became extremely
popular (an 1880 Javal-Schiotz version shown at right). The Javal-Schiotz keratometers have a fixed image size
and are typically “two position.” It uses two self-illuminated objects—one a red square,
the other a green staircase design, which are held on a circumferential track in order to maintain a fixed
distance from the eye. Repeatable, accurate measurements were dependent on the instrument staying focused.
Courtesy of Museum of Vision & Ophthalmic Heritage, San Francisco, CA.