Engraving of a man, holding a perforated mirror in one hand and a lens in the other, examining the eyes of another man, entitled: Early ophthalmoscope, 1873. Ophthalmoscopy is a test that allows a health professional to see inside the fundus of the eye and other structures using an ophthalmoscope. It is done as part of an eye examination and is crucial in determining the health of the retina and the vitreous humor. Hermann Ludwig Ferdinand von Helmholtz (1821-1894) was a German physician and polymath. Trained in physiology, Helmholtz wrote on many topics, ranging from theoretical physics, to the age of the Earth, to the origin of the solar system. As a physiologist and psychologist he is remembered for his mathematics of the eye, theories of vision, ideas on the visual perception of space, color vision research, and on the sensation of tone, perception of sound, and empiricism. In 1851, he revolutionized the field of ophthalmology with the invention of the ophthalmoscope; an instrument used to examine the inside of the human eye. This made him world famous overnight.