The Star Turns Red, the last of his successful plays that had begun with the The Shadow of a Gunman.  
His last play, a satire on the intellectuals of his native city, was entitled Behind the Green Curtains.  Despite the rejection of the expressionistic The Silver Tassie, he wrote another expressionistic work, Within the Gates, which he followed up with the autobiographical Red Roses for Me.  His eyes had already begun to fail while writing 1940's antifascist The Star Turns Red, the last of his successful plays that had begun with the The Shadow of a Gunman.  FTP, name this Abbey Theatre regular best-known for Juno and the Paycock and The Plough and the Stars.
His last play, a satire on the intellectuals of his native city, was entitled Behind the Green Curtains.  
Sean O'Casey