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In the Eastern church, after the words of institution ("This is my body...This is my blood") there is the 'epiklesis.' The epiklesis is a prayer to God the Father that he may send the Holy spirit to transform the bread and wine into Our Lord's body and blood. Here is the text in the Divine liturgy of St. John chrysostom:

Again we offer unto Thee this reasonable and bloodless worship, and we ask Thee, and pray Thee, and supplicate Thee: Send down Thy Holy Spirit upon us and upon these gifts here offered.
And make this bread the precious Body of Thy Christ. (Amen)
And that which is in this cup, the precious Blood of Thy Christ. (Amen)
Making the change by the Holy Spirit. (Amen, Amen, Amen )
That these gifts may be to those who partake for the purification of soul, for remission of sins, for the communion of the Holy Spirit, for the fulfillment of the Kingdom of Heaven; for boldness towards Thee, and not for judgment or condemnation.
Now, in the Western church, transubstantation occurs at the words of institution. But in the East, the bread and wine become the Body and Blood at the epiklesis and not the words of institution. So who is right? And also, do eastern Catholic churches retain the epiklesis?

Yes, I know that. But is the idea that transubstantation occurs at the Words of Institution a dogma that binds the entire Catholic Church (east and west); or is it merely a tradition of the West and therefore not binding in any way to Eastern Catholics? (like Purgatory or the Sacred Heart)