Complex sentence: Subsequently he was a medical assistant to Peter Krukenberg (1788--1865) at Halle, and from 1856 worked under Heinrich Müller (1820--1864) at Würzburg, where he learned microscopic pathology and anatomy of the eye and developed an interest in ophthalmology.
Split into simpler sentences: Subsequently he was a medical assistant to Peter Krukenberg (1788--1865) at Halle, and from 1856 worked under Heinrich Müller (1820--1864) at Würzburg. In Würzburg he learned microscopic pathology and anatomy of the eye, thus developing an interest in ophthalmology.