From the bureau of indispensable knowledge:
Wikipedia: “Multiocular O (ꙮ) is a rare glyph variant of the Cyrillic letter O. This glyph variant can be found in certain manuscripts in the phrase «серафими многоꙮчитїи» (“many-eyed seraphim”). It was documented by Yefim Karsky from a copy of Psalms from around 1429, now found in the collection of the Trinity Lavra of St. Sergius, and subsequently incorporated into Unicode as character U+A66E.”
ETA: This is the manuscript.