An ophthalmometer measures the curvature of the anterior surface of the cornea, and so is used to assess the extent and axis of astigmatism. The German physiologist Hermann von Helmholtz introduced an example in the 1850s. This one, s/n 2529, was made by the General Optical Co. in Mount Vernon, N.Y.; that firm became the General Optical Co., Inc. in 1913. The patent date indicates that it was designed by Ferdinand Buchhop (1858-1934), and assigned to the Meyrowitz Manufacturing Co.
Ref: Ferdinand Buchhop, “Ophthalmometer,” U.S. Patent 1,006,825 (Oct. 24, 1911), assigned to the Meyrowitz Manufacturing Co.