In the apse we see the Christ Most Holy at the centre of a deesis. Wikipedia: “In Byzantine art, and later Eastern Orthodox art generally, the Deësis or Deisis (Greek: δέησις, "prayer" or "supplication"), is a traditional iconic representation of Christ in Majesty or Christ Pantocrator: enthroned, carrying a book, and flanked by the Virgin Mary and St. John the Baptist, and sometimes other saints and angels. Mary and John, and any other figures, are shown facing towards Christ with their hands raised in supplication on behalf of humanity.” and “The presence of Mary and John, and other figures, is one of the differences with the Western Christ in Majesty, where the Four Evangelists and/or their symbols are more commonly included around Christ. The Deesis composition is also commonly found in the West, especially those parts of Italy under Byzantine influence, but also the rest of Europe. It often forms part of a scene of the Last Judgement. The use of the image declined slowly throughout the Middle Ages, and it is never as common as the Western forms of Christ in Majesty.”
A notice indicates this was a burial chapel, an inscription indicates it was dedicated by a nun Martha to her husband Michael Glabas Ducas.