Twenty-three Irish Republican Army prisoners Monday joined a 51-day-old hunger strike by fellow inmates in a move that could increase the chances of violence across Ulster this Christmas season. The British government's Northern Ireland Office confirmed that the men refused breakfast and lunch and vowed to fast until death unless they won recognition as political prisoners rather than criminals. They joined seven inmates who have fasted for 51 days and are confined to the Maze Prison hospital in serious condition. The government also admitted for the first time that one of the original strikers, Sean McKenna, was felt to be in danger of losing his eyesight because of a vitamin deficiency caused by his fast. McKenna was sentenced to 25 years' jail in 1976 for the attempted murder of two police reservists and is considered one of the most determined to fast to death.