Antonie Cramer's explanation of accommodation

In the middle of the last century the question of the origin of accommodation was still unsolved. At the suggestion of Donders, Cramer used in 1851 a microscope to demonstrate that accommodation has to be ascribed to an increase in the curvature of the lens. Donders himself had several instruments made for the same purpose. These are still present in the collection of the Royal Netherlands Ophthalmic Hospital.