The artistic director of the renowned, and in recent years strife-torn, Bolshoi Ballet was returning home from a theatrical celebration with the city’s glitterati when a masked man stepped out of the darkness and threw acid onto his face and eyes.

Sergei Filin, who was attacked about 11:30 p.m. Thursday, suffered third-degree burns. He underwent eye surgery Friday, according to Anatoly Iksanov, the Bolshoi’s director, who said Filin would be flown to Belgium for treatment at a burn clinic.