Complex sentence: He continued to appear as a conductor with the orchestras of Chicago, Cleveland, Berlin, Vienna, Paris and London until early 2012 when he cancelled all conducting engagements after an eye operation left him with severely impaired sight.
Split into simpler sentences: He continued to appear as a conductor with the orchestras of Chicago, Cleveland, Berlin, Vienna, Paris and London. Early in 2012, Boulez cancelled conducting engagements after an eye operation left him with severely impaired sight.