Ophthalmoscope
an instrument invented by Helmholtz, and described by him in 1851. It is used for the examination of the inner structure of the eyeball, and is composed of a small round mirror with a central perforation, which reflects the light of a lamp placed at the side of the eye. When the mirror only is used, the method is known as direct; when a convex lens is between the eye and the mirror it is indirect.