Jesus Cures the Blind
There are several cures of the blind in the gospels, but only Matthew writes of Jesus healing two blind men in the same episode, in each case touching their eyes to heal them (9:27-31 and 20:30-33).
In the mosaic Jesus' healing hand is in the "Old Believers" configuration seen in many of the other panels.
See also a view of the entire left wall with commentary on the iconography of Jesus and the apostles in these mosaics.
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Photographed at the church by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.