Some similarities between Sophocles' Oedipus Rex and Ibsen's Wild Duck lie in the confusion of parentage; tragic ends; tragic hero and heroine being innocent of intentional wrong doing; fate overruling personal choice; true identity unknown to self yet known by others (Chorus/Gregers). Differences between the two plays are that the Chorus is reluctant to tell Oedipus Rex what they know or suspect and Gregers is eager to tell. A corollary of this is that the Chorus anticipates the agonized reaction their news will bring while Gregers is blinded to the truth of how others may react.
To elaborate on some points, neither Oedipus nor Hedvig know their parentage, and neither knows that there is something unknown. In other words, they believe they do know their parentage. Both Oedipus and Hedvig come to tragic ends. In keeping with Aristotelian opinion, Oedipus meets the tragic end of self-inflicted blindness and exile. In keeping with the later Shakespeare model of tragedy, Hedvig dies; her end is also self-inflicted (this reading would tend to cast her death as a self-inflicted punishment instead of what some critics call a self-sacrificial gift).
Gregers stands in opposition to the Chorus in that he is determined in his own mind that the truth will set everyone free from a burden that, ironically, none but Gregers feels or recognizes. The Ekdals are happy in their life of mutual support of weaknesses and strengths. Gregers also opposes the Chorus in that he is unable to shift his point-of-view to that of any other of the characters and consequently believes they will all take his news as a commonplace and make adjustments to accommodate the freedom of truth and begin to be happy.