Феодор Студит
The way in which the bread and wine become the body and blood of Christ has never been dogmatically defined by the Eastern Orthodox Churches. However, St Theodore the Studite writes in his treatise "On the Holy Icons": "for we confess that the faithful receive the very body and blood of Christ, according to the voice of God himself." This was a refutation of the iconoclasts, who insisted that the eucharist was the only true icon of Christ. Thus, it can be argued that by being part of the dogmatic "horos" against the iconoclast heresy, the teaching on the "real presence" of Christ in the eucharist is indeed a dogma of the Eastern Orthodox Church.